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TOMOYO Linux Cross Reference
Linux/mm/huge_memory.c

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  1 // SPDX-License-Identifier: GPL-2.0-only
  2 /*
  3  *  Copyright (C) 2009  Red Hat, Inc.
  4  */
  5 
  6 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  7 
  8 #include <linux/mm.h>
  9 #include <linux/sched.h>
 10 #include <linux/sched/coredump.h>
 11 #include <linux/sched/numa_balancing.h>
 12 #include <linux/highmem.h>
 13 #include <linux/hugetlb.h>
 14 #include <linux/mmu_notifier.h>
 15 #include <linux/rmap.h>
 16 #include <linux/swap.h>
 17 #include <linux/shrinker.h>
 18 #include <linux/mm_inline.h>
 19 #include <linux/swapops.h>
 20 #include <linux/dax.h>
 21 #include <linux/khugepaged.h>
 22 #include <linux/freezer.h>
 23 #include <linux/pfn_t.h>
 24 #include <linux/mman.h>
 25 #include <linux/memremap.h>
 26 #include <linux/pagemap.h>
 27 #include <linux/debugfs.h>
 28 #include <linux/migrate.h>
 29 #include <linux/hashtable.h>
 30 #include <linux/userfaultfd_k.h>
 31 #include <linux/page_idle.h>
 32 #include <linux/shmem_fs.h>
 33 #include <linux/oom.h>
 34 #include <linux/numa.h>
 35 #include <linux/page_owner.h>
 36 
 37 #include <asm/tlb.h>
 38 #include <asm/pgalloc.h>
 39 #include "internal.h"
 40 
 41 /*
 42  * By default, transparent hugepage support is disabled in order to avoid
 43  * risking an increased memory footprint for applications that are not
 44  * guaranteed to benefit from it. When transparent hugepage support is
 45  * enabled, it is for all mappings, and khugepaged scans all mappings.
 46  * Defrag is invoked by khugepaged hugepage allocations and by page faults
 47  * for all hugepage allocations.
 48  */
 49 unsigned long transparent_hugepage_flags __read_mostly =
 50 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
 51         (1<<TRANSPARENT_HUGEPAGE_FLAG)|
 52 #endif
 53 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
 54         (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
 55 #endif
 56         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG)|
 57         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
 58         (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 59 
 60 static struct shrinker deferred_split_shrinker;
 61 
 62 static atomic_t huge_zero_refcount;
 63 struct page *huge_zero_page __read_mostly;
 64 
 65 bool transparent_hugepage_enabled(struct vm_area_struct *vma)
 66 {
 67         /* The addr is used to check if the vma size fits */
 68         unsigned long addr = (vma->vm_end & HPAGE_PMD_MASK) - HPAGE_PMD_SIZE;
 69 
 70         if (!transhuge_vma_suitable(vma, addr))
 71                 return false;
 72         if (vma_is_anonymous(vma))
 73                 return __transparent_hugepage_enabled(vma);
 74         if (vma_is_shmem(vma))
 75                 return shmem_huge_enabled(vma);
 76 
 77         return false;
 78 }
 79 
 80 static struct page *get_huge_zero_page(void)
 81 {
 82         struct page *zero_page;
 83 retry:
 84         if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
 85                 return READ_ONCE(huge_zero_page);
 86 
 87         zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
 88                         HPAGE_PMD_ORDER);
 89         if (!zero_page) {
 90                 count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
 91                 return NULL;
 92         }
 93         count_vm_event(THP_ZERO_PAGE_ALLOC);
 94         preempt_disable();
 95         if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
 96                 preempt_enable();
 97                 __free_pages(zero_page, compound_order(zero_page));
 98                 goto retry;
 99         }
100 
101         /* We take additional reference here. It will be put back by shrinker */
102         atomic_set(&huge_zero_refcount, 2);
103         preempt_enable();
104         return READ_ONCE(huge_zero_page);
105 }
106 
107 static void put_huge_zero_page(void)
108 {
109         /*
110          * Counter should never go to zero here. Only shrinker can put
111          * last reference.
112          */
113         BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
114 }
115 
116 struct page *mm_get_huge_zero_page(struct mm_struct *mm)
117 {
118         if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
119                 return READ_ONCE(huge_zero_page);
120 
121         if (!get_huge_zero_page())
122                 return NULL;
123 
124         if (test_and_set_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
125                 put_huge_zero_page();
126 
127         return READ_ONCE(huge_zero_page);
128 }
129 
130 void mm_put_huge_zero_page(struct mm_struct *mm)
131 {
132         if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
133                 put_huge_zero_page();
134 }
135 
136 static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
137                                         struct shrink_control *sc)
138 {
139         /* we can free zero page only if last reference remains */
140         return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
141 }
142 
143 static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
144                                        struct shrink_control *sc)
145 {
146         if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
147                 struct page *zero_page = xchg(&huge_zero_page, NULL);
148                 BUG_ON(zero_page == NULL);
149                 __free_pages(zero_page, compound_order(zero_page));
150                 return HPAGE_PMD_NR;
151         }
152 
153         return 0;
154 }
155 
156 static struct shrinker huge_zero_page_shrinker = {
157         .count_objects = shrink_huge_zero_page_count,
158         .scan_objects = shrink_huge_zero_page_scan,
159         .seeks = DEFAULT_SEEKS,
160 };
161 
162 #ifdef CONFIG_SYSFS
163 static ssize_t enabled_show(struct kobject *kobj,
164                             struct kobj_attribute *attr, char *buf)
165 {
166         if (test_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags))
167                 return sprintf(buf, "[always] madvise never\n");
168         else if (test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags))
169                 return sprintf(buf, "always [madvise] never\n");
170         else
171                 return sprintf(buf, "always madvise [never]\n");
172 }
173 
174 static ssize_t enabled_store(struct kobject *kobj,
175                              struct kobj_attribute *attr,
176                              const char *buf, size_t count)
177 {
178         ssize_t ret = count;
179 
180         if (!memcmp("always", buf,
181                     min(sizeof("always")-1, count))) {
182                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
183                 set_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
184         } else if (!memcmp("madvise", buf,
185                            min(sizeof("madvise")-1, count))) {
186                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
187                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
188         } else if (!memcmp("never", buf,
189                            min(sizeof("never")-1, count))) {
190                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
191                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
192         } else
193                 ret = -EINVAL;
194 
195         if (ret > 0) {
196                 int err = start_stop_khugepaged();
197                 if (err)
198                         ret = err;
199         }
200         return ret;
201 }
202 static struct kobj_attribute enabled_attr =
203         __ATTR(enabled, 0644, enabled_show, enabled_store);
204 
205 ssize_t single_hugepage_flag_show(struct kobject *kobj,
206                                 struct kobj_attribute *attr, char *buf,
207                                 enum transparent_hugepage_flag flag)
208 {
209         return sprintf(buf, "%d\n",
210                        !!test_bit(flag, &transparent_hugepage_flags));
211 }
212 
213 ssize_t single_hugepage_flag_store(struct kobject *kobj,
214                                  struct kobj_attribute *attr,
215                                  const char *buf, size_t count,
216                                  enum transparent_hugepage_flag flag)
217 {
218         unsigned long value;
219         int ret;
220 
221         ret = kstrtoul(buf, 10, &value);
222         if (ret < 0)
223                 return ret;
224         if (value > 1)
225                 return -EINVAL;
226 
227         if (value)
228                 set_bit(flag, &transparent_hugepage_flags);
229         else
230                 clear_bit(flag, &transparent_hugepage_flags);
231 
232         return count;
233 }
234 
235 static ssize_t defrag_show(struct kobject *kobj,
236                            struct kobj_attribute *attr, char *buf)
237 {
238         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
239                 return sprintf(buf, "[always] defer defer+madvise madvise never\n");
240         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
241                 return sprintf(buf, "always [defer] defer+madvise madvise never\n");
242         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags))
243                 return sprintf(buf, "always defer [defer+madvise] madvise never\n");
244         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
245                 return sprintf(buf, "always defer defer+madvise [madvise] never\n");
246         return sprintf(buf, "always defer defer+madvise madvise [never]\n");
247 }
248 
249 static ssize_t defrag_store(struct kobject *kobj,
250                             struct kobj_attribute *attr,
251                             const char *buf, size_t count)
252 {
253         if (!memcmp("always", buf,
254                     min(sizeof("always")-1, count))) {
255                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
256                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
257                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
258                 set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
259         } else if (!memcmp("defer+madvise", buf,
260                     min(sizeof("defer+madvise")-1, count))) {
261                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
262                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
263                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
264                 set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
265         } else if (!memcmp("defer", buf,
266                     min(sizeof("defer")-1, count))) {
267                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
268                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
269                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
270                 set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
271         } else if (!memcmp("madvise", buf,
272                            min(sizeof("madvise")-1, count))) {
273                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
274                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
275                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
276                 set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
277         } else if (!memcmp("never", buf,
278                            min(sizeof("never")-1, count))) {
279                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
280                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
281                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
282                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
283         } else
284                 return -EINVAL;
285 
286         return count;
287 }
288 static struct kobj_attribute defrag_attr =
289         __ATTR(defrag, 0644, defrag_show, defrag_store);
290 
291 static ssize_t use_zero_page_show(struct kobject *kobj,
292                 struct kobj_attribute *attr, char *buf)
293 {
294         return single_hugepage_flag_show(kobj, attr, buf,
295                                 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
296 }
297 static ssize_t use_zero_page_store(struct kobject *kobj,
298                 struct kobj_attribute *attr, const char *buf, size_t count)
299 {
300         return single_hugepage_flag_store(kobj, attr, buf, count,
301                                  TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
302 }
303 static struct kobj_attribute use_zero_page_attr =
304         __ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
305 
306 static ssize_t hpage_pmd_size_show(struct kobject *kobj,
307                 struct kobj_attribute *attr, char *buf)
308 {
309         return sprintf(buf, "%lu\n", HPAGE_PMD_SIZE);
310 }
311 static struct kobj_attribute hpage_pmd_size_attr =
312         __ATTR_RO(hpage_pmd_size);
313 
314 #ifdef CONFIG_DEBUG_VM
315 static ssize_t debug_cow_show(struct kobject *kobj,
316                                 struct kobj_attribute *attr, char *buf)
317 {
318         return single_hugepage_flag_show(kobj, attr, buf,
319                                 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
320 }
321 static ssize_t debug_cow_store(struct kobject *kobj,
322                                struct kobj_attribute *attr,
323                                const char *buf, size_t count)
324 {
325         return single_hugepage_flag_store(kobj, attr, buf, count,
326                                  TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
327 }
328 static struct kobj_attribute debug_cow_attr =
329         __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
330 #endif /* CONFIG_DEBUG_VM */
331 
332 static struct attribute *hugepage_attr[] = {
333         &enabled_attr.attr,
334         &defrag_attr.attr,
335         &use_zero_page_attr.attr,
336         &hpage_pmd_size_attr.attr,
337 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
338         &shmem_enabled_attr.attr,
339 #endif
340 #ifdef CONFIG_DEBUG_VM
341         &debug_cow_attr.attr,
342 #endif
343         NULL,
344 };
345 
346 static const struct attribute_group hugepage_attr_group = {
347         .attrs = hugepage_attr,
348 };
349 
350 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
351 {
352         int err;
353 
354         *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
355         if (unlikely(!*hugepage_kobj)) {
356                 pr_err("failed to create transparent hugepage kobject\n");
357                 return -ENOMEM;
358         }
359 
360         err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
361         if (err) {
362                 pr_err("failed to register transparent hugepage group\n");
363                 goto delete_obj;
364         }
365 
366         err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
367         if (err) {
368                 pr_err("failed to register transparent hugepage group\n");
369                 goto remove_hp_group;
370         }
371 
372         return 0;
373 
374 remove_hp_group:
375         sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
376 delete_obj:
377         kobject_put(*hugepage_kobj);
378         return err;
379 }
380 
381 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
382 {
383         sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
384         sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
385         kobject_put(hugepage_kobj);
386 }
387 #else
388 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
389 {
390         return 0;
391 }
392 
393 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
394 {
395 }
396 #endif /* CONFIG_SYSFS */
397 
398 static int __init hugepage_init(void)
399 {
400         int err;
401         struct kobject *hugepage_kobj;
402 
403         if (!has_transparent_hugepage()) {
404                 transparent_hugepage_flags = 0;
405                 return -EINVAL;
406         }
407 
408         /*
409          * hugepages can't be allocated by the buddy allocator
410          */
411         MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER >= MAX_ORDER);
412         /*
413          * we use page->mapping and page->index in second tail page
414          * as list_head: assuming THP order >= 2
415          */
416         MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER < 2);
417 
418         err = hugepage_init_sysfs(&hugepage_kobj);
419         if (err)
420                 goto err_sysfs;
421 
422         err = khugepaged_init();
423         if (err)
424                 goto err_slab;
425 
426         err = register_shrinker(&huge_zero_page_shrinker);
427         if (err)
428                 goto err_hzp_shrinker;
429         err = register_shrinker(&deferred_split_shrinker);
430         if (err)
431                 goto err_split_shrinker;
432 
433         /*
434          * By default disable transparent hugepages on smaller systems,
435          * where the extra memory used could hurt more than TLB overhead
436          * is likely to save.  The admin can still enable it through /sys.
437          */
438         if (totalram_pages() < (512 << (20 - PAGE_SHIFT))) {
439                 transparent_hugepage_flags = 0;
440                 return 0;
441         }
442 
443         err = start_stop_khugepaged();
444         if (err)
445                 goto err_khugepaged;
446 
447         return 0;
448 err_khugepaged:
449         unregister_shrinker(&deferred_split_shrinker);
450 err_split_shrinker:
451         unregister_shrinker(&huge_zero_page_shrinker);
452 err_hzp_shrinker:
453         khugepaged_destroy();
454 err_slab:
455         hugepage_exit_sysfs(hugepage_kobj);
456 err_sysfs:
457         return err;
458 }
459 subsys_initcall(hugepage_init);
460 
461 static int __init setup_transparent_hugepage(char *str)
462 {
463         int ret = 0;
464         if (!str)
465                 goto out;
466         if (!strcmp(str, "always")) {
467                 set_bit(TRANSPARENT_HUGEPAGE_FLAG,
468                         &transparent_hugepage_flags);
469                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
470                           &transparent_hugepage_flags);
471                 ret = 1;
472         } else if (!strcmp(str, "madvise")) {
473                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
474                           &transparent_hugepage_flags);
475                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
476                         &transparent_hugepage_flags);
477                 ret = 1;
478         } else if (!strcmp(str, "never")) {
479                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
480                           &transparent_hugepage_flags);
481                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
482                           &transparent_hugepage_flags);
483                 ret = 1;
484         }
485 out:
486         if (!ret)
487                 pr_warn("transparent_hugepage= cannot parse, ignored\n");
488         return ret;
489 }
490 __setup("transparent_hugepage=", setup_transparent_hugepage);
491 
492 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
493 {
494         if (likely(vma->vm_flags & VM_WRITE))
495                 pmd = pmd_mkwrite(pmd);
496         return pmd;
497 }
498 
499 static inline struct list_head *page_deferred_list(struct page *page)
500 {
501         /* ->lru in the tail pages is occupied by compound_head. */
502         return &page[2].deferred_list;
503 }
504 
505 void prep_transhuge_page(struct page *page)
506 {
507         /*
508          * we use page->mapping and page->indexlru in second tail page
509          * as list_head: assuming THP order >= 2
510          */
511 
512         INIT_LIST_HEAD(page_deferred_list(page));
513         set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
514 }
515 
516 static unsigned long __thp_get_unmapped_area(struct file *filp, unsigned long len,
517                 loff_t off, unsigned long flags, unsigned long size)
518 {
519         unsigned long addr;
520         loff_t off_end = off + len;
521         loff_t off_align = round_up(off, size);
522         unsigned long len_pad;
523 
524         if (off_end <= off_align || (off_end - off_align) < size)
525                 return 0;
526 
527         len_pad = len + size;
528         if (len_pad < len || (off + len_pad) < off)
529                 return 0;
530 
531         addr = current->mm->get_unmapped_area(filp, 0, len_pad,
532                                               off >> PAGE_SHIFT, flags);
533         if (IS_ERR_VALUE(addr))
534                 return 0;
535 
536         addr += (off - addr) & (size - 1);
537         return addr;
538 }
539 
540 unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
541                 unsigned long len, unsigned long pgoff, unsigned long flags)
542 {
543         loff_t off = (loff_t)pgoff << PAGE_SHIFT;
544 
545         if (addr)
546                 goto out;
547         if (!IS_DAX(filp->f_mapping->host) || !IS_ENABLED(CONFIG_FS_DAX_PMD))
548                 goto out;
549 
550         addr = __thp_get_unmapped_area(filp, len, off, flags, PMD_SIZE);
551         if (addr)
552                 return addr;
553 
554  out:
555         return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags);
556 }
557 EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
558 
559 static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
560                         struct page *page, gfp_t gfp)
561 {
562         struct vm_area_struct *vma = vmf->vma;
563         struct mem_cgroup *memcg;
564         pgtable_t pgtable;
565         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
566         vm_fault_t ret = 0;
567 
568         VM_BUG_ON_PAGE(!PageCompound(page), page);
569 
570         if (mem_cgroup_try_charge_delay(page, vma->vm_mm, gfp, &memcg, true)) {
571                 put_page(page);
572                 count_vm_event(THP_FAULT_FALLBACK);
573                 return VM_FAULT_FALLBACK;
574         }
575 
576         pgtable = pte_alloc_one(vma->vm_mm);
577         if (unlikely(!pgtable)) {
578                 ret = VM_FAULT_OOM;
579                 goto release;
580         }
581 
582         clear_huge_page(page, vmf->address, HPAGE_PMD_NR);
583         /*
584          * The memory barrier inside __SetPageUptodate makes sure that
585          * clear_huge_page writes become visible before the set_pmd_at()
586          * write.
587          */
588         __SetPageUptodate(page);
589 
590         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
591         if (unlikely(!pmd_none(*vmf->pmd))) {
592                 goto unlock_release;
593         } else {
594                 pmd_t entry;
595 
596                 ret = check_stable_address_space(vma->vm_mm);
597                 if (ret)
598                         goto unlock_release;
599 
600                 /* Deliver the page fault to userland */
601                 if (userfaultfd_missing(vma)) {
602                         vm_fault_t ret2;
603 
604                         spin_unlock(vmf->ptl);
605                         mem_cgroup_cancel_charge(page, memcg, true);
606                         put_page(page);
607                         pte_free(vma->vm_mm, pgtable);
608                         ret2 = handle_userfault(vmf, VM_UFFD_MISSING);
609                         VM_BUG_ON(ret2 & VM_FAULT_FALLBACK);
610                         return ret2;
611                 }
612 
613                 entry = mk_huge_pmd(page, vma->vm_page_prot);
614                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
615                 page_add_new_anon_rmap(page, vma, haddr, true);
616                 mem_cgroup_commit_charge(page, memcg, false, true);
617                 lru_cache_add_active_or_unevictable(page, vma);
618                 pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
619                 set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
620                 add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
621                 mm_inc_nr_ptes(vma->vm_mm);
622                 spin_unlock(vmf->ptl);
623                 count_vm_event(THP_FAULT_ALLOC);
624                 count_memcg_events(memcg, THP_FAULT_ALLOC, 1);
625         }
626 
627         return 0;
628 unlock_release:
629         spin_unlock(vmf->ptl);
630 release:
631         if (pgtable)
632                 pte_free(vma->vm_mm, pgtable);
633         mem_cgroup_cancel_charge(page, memcg, true);
634         put_page(page);
635         return ret;
636 
637 }
638 
639 /*
640  * always: directly stall for all thp allocations
641  * defer: wake kswapd and fail if not immediately available
642  * defer+madvise: wake kswapd and directly stall for MADV_HUGEPAGE, otherwise
643  *                fail if not immediately available
644  * madvise: directly stall for MADV_HUGEPAGE, otherwise fail if not immediately
645  *          available
646  * never: never stall for any thp allocation
647  */
648 static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma, unsigned long addr)
649 {
650         const bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
651         gfp_t this_node = 0;
652 
653 #ifdef CONFIG_NUMA
654         struct mempolicy *pol;
655         /*
656          * __GFP_THISNODE is used only when __GFP_DIRECT_RECLAIM is not
657          * specified, to express a general desire to stay on the current
658          * node for optimistic allocation attempts. If the defrag mode
659          * and/or madvise hint requires the direct reclaim then we prefer
660          * to fallback to other node rather than node reclaim because that
661          * can lead to excessive reclaim even though there is free memory
662          * on other nodes. We expect that NUMA preferences are specified
663          * by memory policies.
664          */
665         pol = get_vma_policy(vma, addr);
666         if (pol->mode != MPOL_BIND)
667                 this_node = __GFP_THISNODE;
668         mpol_cond_put(pol);
669 #endif
670 
671         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
672                 return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY);
673         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
674                 return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM | this_node;
675         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags))
676                 return GFP_TRANSHUGE_LIGHT | (vma_madvised ? __GFP_DIRECT_RECLAIM :
677                                                              __GFP_KSWAPD_RECLAIM | this_node);
678         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
679                 return GFP_TRANSHUGE_LIGHT | (vma_madvised ? __GFP_DIRECT_RECLAIM :
680                                                              this_node);
681         return GFP_TRANSHUGE_LIGHT | this_node;
682 }
683 
684 /* Caller must hold page table lock. */
685 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
686                 struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
687                 struct page *zero_page)
688 {
689         pmd_t entry;
690         if (!pmd_none(*pmd))
691                 return false;
692         entry = mk_pmd(zero_page, vma->vm_page_prot);
693         entry = pmd_mkhuge(entry);
694         if (pgtable)
695                 pgtable_trans_huge_deposit(mm, pmd, pgtable);
696         set_pmd_at(mm, haddr, pmd, entry);
697         mm_inc_nr_ptes(mm);
698         return true;
699 }
700 
701 vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
702 {
703         struct vm_area_struct *vma = vmf->vma;
704         gfp_t gfp;
705         struct page *page;
706         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
707 
708         if (!transhuge_vma_suitable(vma, haddr))
709                 return VM_FAULT_FALLBACK;
710         if (unlikely(anon_vma_prepare(vma)))
711                 return VM_FAULT_OOM;
712         if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
713                 return VM_FAULT_OOM;
714         if (!(vmf->flags & FAULT_FLAG_WRITE) &&
715                         !mm_forbids_zeropage(vma->vm_mm) &&
716                         transparent_hugepage_use_zero_page()) {
717                 pgtable_t pgtable;
718                 struct page *zero_page;
719                 bool set;
720                 vm_fault_t ret;
721                 pgtable = pte_alloc_one(vma->vm_mm);
722                 if (unlikely(!pgtable))
723                         return VM_FAULT_OOM;
724                 zero_page = mm_get_huge_zero_page(vma->vm_mm);
725                 if (unlikely(!zero_page)) {
726                         pte_free(vma->vm_mm, pgtable);
727                         count_vm_event(THP_FAULT_FALLBACK);
728                         return VM_FAULT_FALLBACK;
729                 }
730                 vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
731                 ret = 0;
732                 set = false;
733                 if (pmd_none(*vmf->pmd)) {
734                         ret = check_stable_address_space(vma->vm_mm);
735                         if (ret) {
736                                 spin_unlock(vmf->ptl);
737                         } else if (userfaultfd_missing(vma)) {
738                                 spin_unlock(vmf->ptl);
739                                 ret = handle_userfault(vmf, VM_UFFD_MISSING);
740                                 VM_BUG_ON(ret & VM_FAULT_FALLBACK);
741                         } else {
742                                 set_huge_zero_page(pgtable, vma->vm_mm, vma,
743                                                    haddr, vmf->pmd, zero_page);
744                                 spin_unlock(vmf->ptl);
745                                 set = true;
746                         }
747                 } else
748                         spin_unlock(vmf->ptl);
749                 if (!set)
750                         pte_free(vma->vm_mm, pgtable);
751                 return ret;
752         }
753         gfp = alloc_hugepage_direct_gfpmask(vma, haddr);
754         page = alloc_pages_vma(gfp, HPAGE_PMD_ORDER, vma, haddr, numa_node_id());
755         if (unlikely(!page)) {
756                 count_vm_event(THP_FAULT_FALLBACK);
757                 return VM_FAULT_FALLBACK;
758         }
759         prep_transhuge_page(page);
760         return __do_huge_pmd_anonymous_page(vmf, page, gfp);
761 }
762 
763 static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
764                 pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write,
765                 pgtable_t pgtable)
766 {
767         struct mm_struct *mm = vma->vm_mm;
768         pmd_t entry;
769         spinlock_t *ptl;
770 
771         ptl = pmd_lock(mm, pmd);
772         if (!pmd_none(*pmd)) {
773                 if (write) {
774                         if (pmd_pfn(*pmd) != pfn_t_to_pfn(pfn)) {
775                                 WARN_ON_ONCE(!is_huge_zero_pmd(*pmd));
776                                 goto out_unlock;
777                         }
778                         entry = pmd_mkyoung(*pmd);
779                         entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
780                         if (pmdp_set_access_flags(vma, addr, pmd, entry, 1))
781                                 update_mmu_cache_pmd(vma, addr, pmd);
782                 }
783 
784                 goto out_unlock;
785         }
786 
787         entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
788         if (pfn_t_devmap(pfn))
789                 entry = pmd_mkdevmap(entry);
790         if (write) {
791                 entry = pmd_mkyoung(pmd_mkdirty(entry));
792                 entry = maybe_pmd_mkwrite(entry, vma);
793         }
794 
795         if (pgtable) {
796                 pgtable_trans_huge_deposit(mm, pmd, pgtable);
797                 mm_inc_nr_ptes(mm);
798                 pgtable = NULL;
799         }
800 
801         set_pmd_at(mm, addr, pmd, entry);
802         update_mmu_cache_pmd(vma, addr, pmd);
803 
804 out_unlock:
805         spin_unlock(ptl);
806         if (pgtable)
807                 pte_free(mm, pgtable);
808 }
809 
810 vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write)
811 {
812         unsigned long addr = vmf->address & PMD_MASK;
813         struct vm_area_struct *vma = vmf->vma;
814         pgprot_t pgprot = vma->vm_page_prot;
815         pgtable_t pgtable = NULL;
816 
817         /*
818          * If we had pmd_special, we could avoid all these restrictions,
819          * but we need to be consistent with PTEs and architectures that
820          * can't support a 'special' bit.
821          */
822         BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
823                         !pfn_t_devmap(pfn));
824         BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
825                                                 (VM_PFNMAP|VM_MIXEDMAP));
826         BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
827 
828         if (addr < vma->vm_start || addr >= vma->vm_end)
829                 return VM_FAULT_SIGBUS;
830 
831         if (arch_needs_pgtable_deposit()) {
832                 pgtable = pte_alloc_one(vma->vm_mm);
833                 if (!pgtable)
834                         return VM_FAULT_OOM;
835         }
836 
837         track_pfn_insert(vma, &pgprot, pfn);
838 
839         insert_pfn_pmd(vma, addr, vmf->pmd, pfn, pgprot, write, pgtable);
840         return VM_FAULT_NOPAGE;
841 }
842 EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd);
843 
844 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
845 static pud_t maybe_pud_mkwrite(pud_t pud, struct vm_area_struct *vma)
846 {
847         if (likely(vma->vm_flags & VM_WRITE))
848                 pud = pud_mkwrite(pud);
849         return pud;
850 }
851 
852 static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
853                 pud_t *pud, pfn_t pfn, pgprot_t prot, bool write)
854 {
855         struct mm_struct *mm = vma->vm_mm;
856         pud_t entry;
857         spinlock_t *ptl;
858 
859         ptl = pud_lock(mm, pud);
860         if (!pud_none(*pud)) {
861                 if (write) {
862                         if (pud_pfn(*pud) != pfn_t_to_pfn(pfn)) {
863                                 WARN_ON_ONCE(!is_huge_zero_pud(*pud));
864                                 goto out_unlock;
865                         }
866                         entry = pud_mkyoung(*pud);
867                         entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma);
868                         if (pudp_set_access_flags(vma, addr, pud, entry, 1))
869                                 update_mmu_cache_pud(vma, addr, pud);
870                 }
871                 goto out_unlock;
872         }
873 
874         entry = pud_mkhuge(pfn_t_pud(pfn, prot));
875         if (pfn_t_devmap(pfn))
876                 entry = pud_mkdevmap(entry);
877         if (write) {
878                 entry = pud_mkyoung(pud_mkdirty(entry));
879                 entry = maybe_pud_mkwrite(entry, vma);
880         }
881         set_pud_at(mm, addr, pud, entry);
882         update_mmu_cache_pud(vma, addr, pud);
883 
884 out_unlock:
885         spin_unlock(ptl);
886 }
887 
888 vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write)
889 {
890         unsigned long addr = vmf->address & PUD_MASK;
891         struct vm_area_struct *vma = vmf->vma;
892         pgprot_t pgprot = vma->vm_page_prot;
893 
894         /*
895          * If we had pud_special, we could avoid all these restrictions,
896          * but we need to be consistent with PTEs and architectures that
897          * can't support a 'special' bit.
898          */
899         BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
900                         !pfn_t_devmap(pfn));
901         BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
902                                                 (VM_PFNMAP|VM_MIXEDMAP));
903         BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
904 
905         if (addr < vma->vm_start || addr >= vma->vm_end)
906                 return VM_FAULT_SIGBUS;
907 
908         track_pfn_insert(vma, &pgprot, pfn);
909 
910         insert_pfn_pud(vma, addr, vmf->pud, pfn, pgprot, write);
911         return VM_FAULT_NOPAGE;
912 }
913 EXPORT_SYMBOL_GPL(vmf_insert_pfn_pud);
914 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
915 
916 static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
917                 pmd_t *pmd, int flags)
918 {
919         pmd_t _pmd;
920 
921         _pmd = pmd_mkyoung(*pmd);
922         if (flags & FOLL_WRITE)
923                 _pmd = pmd_mkdirty(_pmd);
924         if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
925                                 pmd, _pmd, flags & FOLL_WRITE))
926                 update_mmu_cache_pmd(vma, addr, pmd);
927 }
928 
929 struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
930                 pmd_t *pmd, int flags, struct dev_pagemap **pgmap)
931 {
932         unsigned long pfn = pmd_pfn(*pmd);
933         struct mm_struct *mm = vma->vm_mm;
934         struct page *page;
935 
936         assert_spin_locked(pmd_lockptr(mm, pmd));
937 
938         /*
939          * When we COW a devmap PMD entry, we split it into PTEs, so we should
940          * not be in this function with `flags & FOLL_COW` set.
941          */
942         WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");
943 
944         if (flags & FOLL_WRITE && !pmd_write(*pmd))
945                 return NULL;
946 
947         if (pmd_present(*pmd) && pmd_devmap(*pmd))
948                 /* pass */;
949         else
950                 return NULL;
951 
952         if (flags & FOLL_TOUCH)
953                 touch_pmd(vma, addr, pmd, flags);
954 
955         /*
956          * device mapped pages can only be returned if the
957          * caller will manage the page reference count.
958          */
959         if (!(flags & FOLL_GET))
960                 return ERR_PTR(-EEXIST);
961 
962         pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
963         *pgmap = get_dev_pagemap(pfn, *pgmap);
964         if (!*pgmap)
965                 return ERR_PTR(-EFAULT);
966         page = pfn_to_page(pfn);
967         get_page(page);
968 
969         return page;
970 }
971 
972 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
973                   pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
974                   struct vm_area_struct *vma)
975 {
976         spinlock_t *dst_ptl, *src_ptl;
977         struct page *src_page;
978         pmd_t pmd;
979         pgtable_t pgtable = NULL;
980         int ret = -ENOMEM;
981 
982         /* Skip if can be re-fill on fault */
983         if (!vma_is_anonymous(vma))
984                 return 0;
985 
986         pgtable = pte_alloc_one(dst_mm);
987         if (unlikely(!pgtable))
988                 goto out;
989 
990         dst_ptl = pmd_lock(dst_mm, dst_pmd);
991         src_ptl = pmd_lockptr(src_mm, src_pmd);
992         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
993 
994         ret = -EAGAIN;
995         pmd = *src_pmd;
996 
997 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
998         if (unlikely(is_swap_pmd(pmd))) {
999                 swp_entry_t entry = pmd_to_swp_entry(pmd);
1000 
1001                 VM_BUG_ON(!is_pmd_migration_entry(pmd));
1002                 if (is_write_migration_entry(entry)) {
1003                         make_migration_entry_read(&entry);
1004                         pmd = swp_entry_to_pmd(entry);
1005                         if (pmd_swp_soft_dirty(*src_pmd))
1006                                 pmd = pmd_swp_mksoft_dirty(pmd);
1007                         set_pmd_at(src_mm, addr, src_pmd, pmd);
1008                 }
1009                 add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
1010                 mm_inc_nr_ptes(dst_mm);
1011                 pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
1012                 set_pmd_at(dst_mm, addr, dst_pmd, pmd);
1013                 ret = 0;
1014                 goto out_unlock;
1015         }
1016 #endif
1017 
1018         if (unlikely(!pmd_trans_huge(pmd))) {
1019                 pte_free(dst_mm, pgtable);
1020                 goto out_unlock;
1021         }
1022         /*
1023          * When page table lock is held, the huge zero pmd should not be
1024          * under splitting since we don't split the page itself, only pmd to
1025          * a page table.
1026          */
1027         if (is_huge_zero_pmd(pmd)) {
1028                 struct page *zero_page;
1029                 /*
1030                  * get_huge_zero_page() will never allocate a new page here,
1031                  * since we already have a zero page to copy. It just takes a
1032                  * reference.
1033                  */
1034                 zero_page = mm_get_huge_zero_page(dst_mm);
1035                 set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
1036                                 zero_page);
1037                 ret = 0;
1038                 goto out_unlock;
1039         }
1040 
1041         src_page = pmd_page(pmd);
1042         VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
1043         get_page(src_page);
1044         page_dup_rmap(src_page, true);
1045         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
1046         mm_inc_nr_ptes(dst_mm);
1047         pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
1048 
1049         pmdp_set_wrprotect(src_mm, addr, src_pmd);
1050         pmd = pmd_mkold(pmd_wrprotect(pmd));
1051         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
1052 
1053         ret = 0;
1054 out_unlock:
1055         spin_unlock(src_ptl);
1056         spin_unlock(dst_ptl);
1057 out:
1058         return ret;
1059 }
1060 
1061 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
1062 static void touch_pud(struct vm_area_struct *vma, unsigned long addr,
1063                 pud_t *pud, int flags)
1064 {
1065         pud_t _pud;
1066 
1067         _pud = pud_mkyoung(*pud);
1068         if (flags & FOLL_WRITE)
1069                 _pud = pud_mkdirty(_pud);
1070         if (pudp_set_access_flags(vma, addr & HPAGE_PUD_MASK,
1071                                 pud, _pud, flags & FOLL_WRITE))
1072                 update_mmu_cache_pud(vma, addr, pud);
1073 }
1074 
1075 struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
1076                 pud_t *pud, int flags, struct dev_pagemap **pgmap)
1077 {
1078         unsigned long pfn = pud_pfn(*pud);
1079         struct mm_struct *mm = vma->vm_mm;
1080         struct page *page;
1081 
1082         assert_spin_locked(pud_lockptr(mm, pud));
1083 
1084         if (flags & FOLL_WRITE && !pud_write(*pud))
1085                 return NULL;
1086 
1087         if (pud_present(*pud) && pud_devmap(*pud))
1088                 /* pass */;
1089         else
1090                 return NULL;
1091 
1092         if (flags & FOLL_TOUCH)
1093                 touch_pud(vma, addr, pud, flags);
1094 
1095         /*
1096          * device mapped pages can only be returned if the
1097          * caller will manage the page reference count.
1098          */
1099         if (!(flags & FOLL_GET))
1100                 return ERR_PTR(-EEXIST);
1101 
1102         pfn += (addr & ~PUD_MASK) >> PAGE_SHIFT;
1103         *pgmap = get_dev_pagemap(pfn, *pgmap);
1104         if (!*pgmap)
1105                 return ERR_PTR(-EFAULT);
1106         page = pfn_to_page(pfn);
1107         get_page(page);
1108 
1109         return page;
1110 }
1111 
1112 int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
1113                   pud_t *dst_pud, pud_t *src_pud, unsigned long addr,
1114                   struct vm_area_struct *vma)
1115 {
1116         spinlock_t *dst_ptl, *src_ptl;
1117         pud_t pud;
1118         int ret;
1119 
1120         dst_ptl = pud_lock(dst_mm, dst_pud);
1121         src_ptl = pud_lockptr(src_mm, src_pud);
1122         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
1123 
1124         ret = -EAGAIN;
1125         pud = *src_pud;
1126         if (unlikely(!pud_trans_huge(pud) && !pud_devmap(pud)))
1127                 goto out_unlock;
1128 
1129         /*
1130          * When page table lock is held, the huge zero pud should not be
1131          * under splitting since we don't split the page itself, only pud to
1132          * a page table.
1133          */
1134         if (is_huge_zero_pud(pud)) {
1135                 /* No huge zero pud yet */
1136         }
1137 
1138         pudp_set_wrprotect(src_mm, addr, src_pud);
1139         pud = pud_mkold(pud_wrprotect(pud));
1140         set_pud_at(dst_mm, addr, dst_pud, pud);
1141 
1142         ret = 0;
1143 out_unlock:
1144         spin_unlock(src_ptl);
1145         spin_unlock(dst_ptl);
1146         return ret;
1147 }
1148 
1149 void huge_pud_set_accessed(struct vm_fault *vmf, pud_t orig_pud)
1150 {
1151         pud_t entry;
1152         unsigned long haddr;
1153         bool write = vmf->flags & FAULT_FLAG_WRITE;
1154 
1155         vmf->ptl = pud_lock(vmf->vma->vm_mm, vmf->pud);
1156         if (unlikely(!pud_same(*vmf->pud, orig_pud)))
1157                 goto unlock;
1158 
1159         entry = pud_mkyoung(orig_pud);
1160         if (write)
1161                 entry = pud_mkdirty(entry);
1162         haddr = vmf->address & HPAGE_PUD_MASK;
1163         if (pudp_set_access_flags(vmf->vma, haddr, vmf->pud, entry, write))
1164                 update_mmu_cache_pud(vmf->vma, vmf->address, vmf->pud);
1165 
1166 unlock:
1167         spin_unlock(vmf->ptl);
1168 }
1169 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
1170 
1171 void huge_pmd_set_accessed(struct vm_fault *vmf, pmd_t orig_pmd)
1172 {
1173         pmd_t entry;
1174         unsigned long haddr;
1175         bool write = vmf->flags & FAULT_FLAG_WRITE;
1176 
1177         vmf->ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
1178         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
1179                 goto unlock;
1180 
1181         entry = pmd_mkyoung(orig_pmd);
1182         if (write)
1183                 entry = pmd_mkdirty(entry);
1184         haddr = vmf->address & HPAGE_PMD_MASK;
1185         if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry, write))
1186                 update_mmu_cache_pmd(vmf->vma, vmf->address, vmf->pmd);
1187 
1188 unlock:
1189         spin_unlock(vmf->ptl);
1190 }
1191 
1192 static vm_fault_t do_huge_pmd_wp_page_fallback(struct vm_fault *vmf,
1193                         pmd_t orig_pmd, struct page *page)
1194 {
1195         struct vm_area_struct *vma = vmf->vma;
1196         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
1197         struct mem_cgroup *memcg;
1198         pgtable_t pgtable;
1199         pmd_t _pmd;
1200         int i;
1201         vm_fault_t ret = 0;
1202         struct page **pages;
1203         struct mmu_notifier_range range;
1204 
1205         pages = kmalloc_array(HPAGE_PMD_NR, sizeof(struct page *),
1206                               GFP_KERNEL);
1207         if (unlikely(!pages)) {
1208                 ret |= VM_FAULT_OOM;
1209                 goto out;
1210         }
1211 
1212         for (i = 0; i < HPAGE_PMD_NR; i++) {
1213                 pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE, vma,
1214                                                vmf->address, page_to_nid(page));
1215                 if (unlikely(!pages[i] ||
1216                              mem_cgroup_try_charge_delay(pages[i], vma->vm_mm,
1217                                      GFP_KERNEL, &memcg, false))) {
1218                         if (pages[i])
1219                                 put_page(pages[i]);
1220                         while (--i >= 0) {
1221                                 memcg = (void *)page_private(pages[i]);
1222                                 set_page_private(pages[i], 0);
1223                                 mem_cgroup_cancel_charge(pages[i], memcg,
1224                                                 false);
1225                                 put_page(pages[i]);
1226                         }
1227                         kfree(pages);
1228                         ret |= VM_FAULT_OOM;
1229                         goto out;
1230                 }
1231                 set_page_private(pages[i], (unsigned long)memcg);
1232         }
1233 
1234         for (i = 0; i < HPAGE_PMD_NR; i++) {
1235                 copy_user_highpage(pages[i], page + i,
1236                                    haddr + PAGE_SIZE * i, vma);
1237                 __SetPageUptodate(pages[i]);
1238                 cond_resched();
1239         }
1240 
1241         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
1242                                 haddr, haddr + HPAGE_PMD_SIZE);
1243         mmu_notifier_invalidate_range_start(&range);
1244 
1245         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
1246         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
1247                 goto out_free_pages;
1248         VM_BUG_ON_PAGE(!PageHead(page), page);
1249 
1250         /*
1251          * Leave pmd empty until pte is filled note we must notify here as
1252          * concurrent CPU thread might write to new page before the call to
1253          * mmu_notifier_invalidate_range_end() happens which can lead to a
1254          * device seeing memory write in different order than CPU.
1255          *
1256          * See Documentation/vm/mmu_notifier.rst
1257          */
1258         pmdp_huge_clear_flush_notify(vma, haddr, vmf->pmd);
1259 
1260         pgtable = pgtable_trans_huge_withdraw(vma->vm_mm, vmf->pmd);
1261         pmd_populate(vma->vm_mm, &_pmd, pgtable);
1262 
1263         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1264                 pte_t entry;
1265                 entry = mk_pte(pages[i], vma->vm_page_prot);
1266                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1267                 memcg = (void *)page_private(pages[i]);
1268                 set_page_private(pages[i], 0);
1269                 page_add_new_anon_rmap(pages[i], vmf->vma, haddr, false);
1270                 mem_cgroup_commit_charge(pages[i], memcg, false, false);
1271                 lru_cache_add_active_or_unevictable(pages[i], vma);
1272                 vmf->pte = pte_offset_map(&_pmd, haddr);
1273                 VM_BUG_ON(!pte_none(*vmf->pte));
1274                 set_pte_at(vma->vm_mm, haddr, vmf->pte, entry);
1275                 pte_unmap(vmf->pte);
1276         }
1277         kfree(pages);
1278 
1279         smp_wmb(); /* make pte visible before pmd */
1280         pmd_populate(vma->vm_mm, vmf->pmd, pgtable);
1281         page_remove_rmap(page, true);
1282         spin_unlock(vmf->ptl);
1283 
1284         /*
1285          * No need to double call mmu_notifier->invalidate_range() callback as
1286          * the above pmdp_huge_clear_flush_notify() did already call it.
1287          */
1288         mmu_notifier_invalidate_range_only_end(&range);
1289 
1290         ret |= VM_FAULT_WRITE;
1291         put_page(page);
1292 
1293 out:
1294         return ret;
1295 
1296 out_free_pages:
1297         spin_unlock(vmf->ptl);
1298         mmu_notifier_invalidate_range_end(&range);
1299         for (i = 0; i < HPAGE_PMD_NR; i++) {
1300                 memcg = (void *)page_private(pages[i]);
1301                 set_page_private(pages[i], 0);
1302                 mem_cgroup_cancel_charge(pages[i], memcg, false);
1303                 put_page(pages[i]);
1304         }
1305         kfree(pages);
1306         goto out;
1307 }
1308 
1309 vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
1310 {
1311         struct vm_area_struct *vma = vmf->vma;
1312         struct page *page = NULL, *new_page;
1313         struct mem_cgroup *memcg;
1314         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
1315         struct mmu_notifier_range range;
1316         gfp_t huge_gfp;                 /* for allocation and charge */
1317         vm_fault_t ret = 0;
1318 
1319         vmf->ptl = pmd_lockptr(vma->vm_mm, vmf->pmd);
1320         VM_BUG_ON_VMA(!vma->anon_vma, vma);
1321         if (is_huge_zero_pmd(orig_pmd))
1322                 goto alloc;
1323         spin_lock(vmf->ptl);
1324         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
1325                 goto out_unlock;
1326 
1327         page = pmd_page(orig_pmd);
1328         VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
1329         /*
1330          * We can only reuse the page if nobody else maps the huge page or it's
1331          * part.
1332          */
1333         if (!trylock_page(page)) {
1334                 get_page(page);
1335                 spin_unlock(vmf->ptl);
1336                 lock_page(page);
1337                 spin_lock(vmf->ptl);
1338                 if (unlikely(!pmd_same(*vmf->pmd, orig_pmd))) {
1339                         unlock_page(page);
1340                         put_page(page);
1341                         goto out_unlock;
1342                 }
1343                 put_page(page);
1344         }
1345         if (reuse_swap_page(page, NULL)) {
1346                 pmd_t entry;
1347                 entry = pmd_mkyoung(orig_pmd);
1348                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1349                 if (pmdp_set_access_flags(vma, haddr, vmf->pmd, entry,  1))
1350                         update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
1351                 ret |= VM_FAULT_WRITE;
1352                 unlock_page(page);
1353                 goto out_unlock;
1354         }
1355         unlock_page(page);
1356         get_page(page);
1357         spin_unlock(vmf->ptl);
1358 alloc:
1359         if (__transparent_hugepage_enabled(vma) &&
1360             !transparent_hugepage_debug_cow()) {
1361                 huge_gfp = alloc_hugepage_direct_gfpmask(vma, haddr);
1362                 new_page = alloc_pages_vma(huge_gfp, HPAGE_PMD_ORDER, vma,
1363                                 haddr, numa_node_id());
1364         } else
1365                 new_page = NULL;
1366 
1367         if (likely(new_page)) {
1368                 prep_transhuge_page(new_page);
1369         } else {
1370                 if (!page) {
1371                         split_huge_pmd(vma, vmf->pmd, vmf->address);
1372                         ret |= VM_FAULT_FALLBACK;
1373                 } else {
1374                         ret = do_huge_pmd_wp_page_fallback(vmf, orig_pmd, page);
1375                         if (ret & VM_FAULT_OOM) {
1376                                 split_huge_pmd(vma, vmf->pmd, vmf->address);
1377                                 ret |= VM_FAULT_FALLBACK;
1378                         }
1379                         put_page(page);
1380                 }
1381                 count_vm_event(THP_FAULT_FALLBACK);
1382                 goto out;
1383         }
1384 
1385         if (unlikely(mem_cgroup_try_charge_delay(new_page, vma->vm_mm,
1386                                         huge_gfp, &memcg, true))) {
1387                 put_page(new_page);
1388                 split_huge_pmd(vma, vmf->pmd, vmf->address);
1389                 if (page)
1390                         put_page(page);
1391                 ret |= VM_FAULT_FALLBACK;
1392                 count_vm_event(THP_FAULT_FALLBACK);
1393                 goto out;
1394         }
1395 
1396         count_vm_event(THP_FAULT_ALLOC);
1397         count_memcg_events(memcg, THP_FAULT_ALLOC, 1);
1398 
1399         if (!page)
1400                 clear_huge_page(new_page, vmf->address, HPAGE_PMD_NR);
1401         else
1402                 copy_user_huge_page(new_page, page, vmf->address,
1403                                     vma, HPAGE_PMD_NR);
1404         __SetPageUptodate(new_page);
1405 
1406         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
1407                                 haddr, haddr + HPAGE_PMD_SIZE);
1408         mmu_notifier_invalidate_range_start(&range);
1409 
1410         spin_lock(vmf->ptl);
1411         if (page)
1412                 put_page(page);
1413         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd))) {
1414                 spin_unlock(vmf->ptl);
1415                 mem_cgroup_cancel_charge(new_page, memcg, true);
1416                 put_page(new_page);
1417                 goto out_mn;
1418         } else {
1419                 pmd_t entry;
1420                 entry = mk_huge_pmd(new_page, vma->vm_page_prot);
1421                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1422                 pmdp_huge_clear_flush_notify(vma, haddr, vmf->pmd);
1423                 page_add_new_anon_rmap(new_page, vma, haddr, true);
1424                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1425                 lru_cache_add_active_or_unevictable(new_page, vma);
1426                 set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
1427                 update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
1428                 if (!page) {
1429                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
1430                 } else {
1431                         VM_BUG_ON_PAGE(!PageHead(page), page);
1432                         page_remove_rmap(page, true);
1433                         put_page(page);
1434                 }
1435                 ret |= VM_FAULT_WRITE;
1436         }
1437         spin_unlock(vmf->ptl);
1438 out_mn:
1439         /*
1440          * No need to double call mmu_notifier->invalidate_range() callback as
1441          * the above pmdp_huge_clear_flush_notify() did already call it.
1442          */
1443         mmu_notifier_invalidate_range_only_end(&range);
1444 out:
1445         return ret;
1446 out_unlock:
1447         spin_unlock(vmf->ptl);
1448         return ret;
1449 }
1450 
1451 /*
1452  * FOLL_FORCE can write to even unwritable pmd's, but only
1453  * after we've gone through a COW cycle and they are dirty.
1454  */
1455 static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags)
1456 {
1457         return pmd_write(pmd) ||
1458                ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd));
1459 }
1460 
1461 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1462                                    unsigned long addr,
1463                                    pmd_t *pmd,
1464                                    unsigned int flags)
1465 {
1466         struct mm_struct *mm = vma->vm_mm;
1467         struct page *page = NULL;
1468 
1469         assert_spin_locked(pmd_lockptr(mm, pmd));
1470 
1471         if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags))
1472                 goto out;
1473 
1474         /* Avoid dumping huge zero page */
1475         if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1476                 return ERR_PTR(-EFAULT);
1477 
1478         /* Full NUMA hinting faults to serialise migration in fault paths */
1479         if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
1480                 goto out;
1481 
1482         page = pmd_page(*pmd);
1483         VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
1484         if (flags & FOLL_TOUCH)
1485                 touch_pmd(vma, addr, pmd, flags);
1486         if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
1487                 /*
1488                  * We don't mlock() pte-mapped THPs. This way we can avoid
1489                  * leaking mlocked pages into non-VM_LOCKED VMAs.
1490                  *
1491                  * For anon THP:
1492                  *
1493                  * In most cases the pmd is the only mapping of the page as we
1494                  * break COW for the mlock() -- see gup_flags |= FOLL_WRITE for
1495                  * writable private mappings in populate_vma_page_range().
1496                  *
1497                  * The only scenario when we have the page shared here is if we
1498                  * mlocking read-only mapping shared over fork(). We skip
1499                  * mlocking such pages.
1500                  *
1501                  * For file THP:
1502                  *
1503                  * We can expect PageDoubleMap() to be stable under page lock:
1504                  * for file pages we set it in page_add_file_rmap(), which
1505                  * requires page to be locked.
1506                  */
1507 
1508                 if (PageAnon(page) && compound_mapcount(page) != 1)
1509                         goto skip_mlock;
1510                 if (PageDoubleMap(page) || !page->mapping)
1511                         goto skip_mlock;
1512                 if (!trylock_page(page))
1513                         goto skip_mlock;
1514                 lru_add_drain();
1515                 if (page->mapping && !PageDoubleMap(page))
1516                         mlock_vma_page(page);
1517                 unlock_page(page);
1518         }
1519 skip_mlock:
1520         page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1521         VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
1522         if (flags & FOLL_GET)
1523                 get_page(page);
1524 
1525 out:
1526         return page;
1527 }
1528 
1529 /* NUMA hinting page fault entry point for trans huge pmds */
1530 vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t pmd)
1531 {
1532         struct vm_area_struct *vma = vmf->vma;
1533         struct anon_vma *anon_vma = NULL;
1534         struct page *page;
1535         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
1536         int page_nid = NUMA_NO_NODE, this_nid = numa_node_id();
1537         int target_nid, last_cpupid = -1;
1538         bool page_locked;
1539         bool migrated = false;
1540         bool was_writable;
1541         int flags = 0;
1542 
1543         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
1544         if (unlikely(!pmd_same(pmd, *vmf->pmd)))
1545                 goto out_unlock;
1546 
1547         /*
1548          * If there are potential migrations, wait for completion and retry
1549          * without disrupting NUMA hinting information. Do not relock and
1550          * check_same as the page may no longer be mapped.
1551          */
1552         if (unlikely(pmd_trans_migrating(*vmf->pmd))) {
1553                 page = pmd_page(*vmf->pmd);
1554                 if (!get_page_unless_zero(page))
1555                         goto out_unlock;
1556                 spin_unlock(vmf->ptl);
1557                 put_and_wait_on_page_locked(page);
1558                 goto out;
1559         }
1560 
1561         page = pmd_page(pmd);
1562         BUG_ON(is_huge_zero_page(page));
1563         page_nid = page_to_nid(page);
1564         last_cpupid = page_cpupid_last(page);
1565         count_vm_numa_event(NUMA_HINT_FAULTS);
1566         if (page_nid == this_nid) {
1567                 count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1568                 flags |= TNF_FAULT_LOCAL;
1569         }
1570 
1571         /* See similar comment in do_numa_page for explanation */
1572         if (!pmd_savedwrite(pmd))
1573                 flags |= TNF_NO_GROUP;
1574 
1575         /*
1576          * Acquire the page lock to serialise THP migrations but avoid dropping
1577          * page_table_lock if at all possible
1578          */
1579         page_locked = trylock_page(page);
1580         target_nid = mpol_misplaced(page, vma, haddr);
1581         if (target_nid == NUMA_NO_NODE) {
1582                 /* If the page was locked, there are no parallel migrations */
1583                 if (page_locked)
1584                         goto clear_pmdnuma;
1585         }
1586 
1587         /* Migration could have started since the pmd_trans_migrating check */
1588         if (!page_locked) {
1589                 page_nid = NUMA_NO_NODE;
1590                 if (!get_page_unless_zero(page))
1591                         goto out_unlock;
1592                 spin_unlock(vmf->ptl);
1593                 put_and_wait_on_page_locked(page);
1594                 goto out;
1595         }
1596 
1597         /*
1598          * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
1599          * to serialises splits
1600          */
1601         get_page(page);
1602         spin_unlock(vmf->ptl);
1603         anon_vma = page_lock_anon_vma_read(page);
1604 
1605         /* Confirm the PMD did not change while page_table_lock was released */
1606         spin_lock(vmf->ptl);
1607         if (unlikely(!pmd_same(pmd, *vmf->pmd))) {
1608                 unlock_page(page);
1609                 put_page(page);
1610                 page_nid = NUMA_NO_NODE;
1611                 goto out_unlock;
1612         }
1613 
1614         /* Bail if we fail to protect against THP splits for any reason */
1615         if (unlikely(!anon_vma)) {
1616                 put_page(page);
1617                 page_nid = NUMA_NO_NODE;
1618                 goto clear_pmdnuma;
1619         }
1620 
1621         /*
1622          * Since we took the NUMA fault, we must have observed the !accessible
1623          * bit. Make sure all other CPUs agree with that, to avoid them
1624          * modifying the page we're about to migrate.
1625          *
1626          * Must be done under PTL such that we'll observe the relevant
1627          * inc_tlb_flush_pending().
1628          *
1629          * We are not sure a pending tlb flush here is for a huge page
1630          * mapping or not. Hence use the tlb range variant
1631          */
1632         if (mm_tlb_flush_pending(vma->vm_mm)) {
1633                 flush_tlb_range(vma, haddr, haddr + HPAGE_PMD_SIZE);
1634                 /*
1635                  * change_huge_pmd() released the pmd lock before
1636                  * invalidating the secondary MMUs sharing the primary
1637                  * MMU pagetables (with ->invalidate_range()). The
1638                  * mmu_notifier_invalidate_range_end() (which
1639                  * internally calls ->invalidate_range()) in
1640                  * change_pmd_range() will run after us, so we can't
1641                  * rely on it here and we need an explicit invalidate.
1642                  */
1643                 mmu_notifier_invalidate_range(vma->vm_mm, haddr,
1644                                               haddr + HPAGE_PMD_SIZE);
1645         }
1646 
1647         /*
1648          * Migrate the THP to the requested node, returns with page unlocked
1649          * and access rights restored.
1650          */
1651         spin_unlock(vmf->ptl);
1652 
1653         migrated = migrate_misplaced_transhuge_page(vma->vm_mm, vma,
1654                                 vmf->pmd, pmd, vmf->address, page, target_nid);
1655         if (migrated) {
1656                 flags |= TNF_MIGRATED;
1657                 page_nid = target_nid;
1658         } else
1659                 flags |= TNF_MIGRATE_FAIL;
1660 
1661         goto out;
1662 clear_pmdnuma:
1663         BUG_ON(!PageLocked(page));
1664         was_writable = pmd_savedwrite(pmd);
1665         pmd = pmd_modify(pmd, vma->vm_page_prot);
1666         pmd = pmd_mkyoung(pmd);
1667         if (was_writable)
1668                 pmd = pmd_mkwrite(pmd);
1669         set_pmd_at(vma->vm_mm, haddr, vmf->pmd, pmd);
1670         update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
1671         unlock_page(page);
1672 out_unlock:
1673         spin_unlock(vmf->ptl);
1674 
1675 out:
1676         if (anon_vma)
1677                 page_unlock_anon_vma_read(anon_vma);
1678 
1679         if (page_nid != NUMA_NO_NODE)
1680                 task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR,
1681                                 flags);
1682 
1683         return 0;
1684 }
1685 
1686 /*
1687  * Return true if we do MADV_FREE successfully on entire pmd page.
1688  * Otherwise, return false.
1689  */
1690 bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1691                 pmd_t *pmd, unsigned long addr, unsigned long next)
1692 {
1693         spinlock_t *ptl;
1694         pmd_t orig_pmd;
1695         struct page *page;
1696         struct mm_struct *mm = tlb->mm;
1697         bool ret = false;
1698 
1699         tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
1700 
1701         ptl = pmd_trans_huge_lock(pmd, vma);
1702         if (!ptl)
1703                 goto out_unlocked;
1704 
1705         orig_pmd = *pmd;
1706         if (is_huge_zero_pmd(orig_pmd))
1707                 goto out;
1708 
1709         if (unlikely(!pmd_present(orig_pmd))) {
1710                 VM_BUG_ON(thp_migration_supported() &&
1711                                   !is_pmd_migration_entry(orig_pmd));
1712                 goto out;
1713         }
1714 
1715         page = pmd_page(orig_pmd);
1716         /*
1717          * If other processes are mapping this page, we couldn't discard
1718          * the page unless they all do MADV_FREE so let's skip the page.
1719          */
1720         if (page_mapcount(page) != 1)
1721                 goto out;
1722 
1723         if (!trylock_page(page))
1724                 goto out;
1725 
1726         /*
1727          * If user want to discard part-pages of THP, split it so MADV_FREE
1728          * will deactivate only them.
1729          */
1730         if (next - addr != HPAGE_PMD_SIZE) {
1731                 get_page(page);
1732                 spin_unlock(ptl);
1733                 split_huge_page(page);
1734                 unlock_page(page);
1735                 put_page(page);
1736                 goto out_unlocked;
1737         }
1738 
1739         if (PageDirty(page))
1740                 ClearPageDirty(page);
1741         unlock_page(page);
1742 
1743         if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
1744                 pmdp_invalidate(vma, addr, pmd);
1745                 orig_pmd = pmd_mkold(orig_pmd);
1746                 orig_pmd = pmd_mkclean(orig_pmd);
1747 
1748                 set_pmd_at(mm, addr, pmd, orig_pmd);
1749                 tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1750         }
1751 
1752         mark_page_lazyfree(page);
1753         ret = true;
1754 out:
1755         spin_unlock(ptl);
1756 out_unlocked:
1757         return ret;
1758 }
1759 
1760 static inline void zap_deposited_table(struct mm_struct *mm, pmd_t *pmd)
1761 {
1762         pgtable_t pgtable;
1763 
1764         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1765         pte_free(mm, pgtable);
1766         mm_dec_nr_ptes(mm);
1767 }
1768 
1769 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1770                  pmd_t *pmd, unsigned long addr)
1771 {
1772         pmd_t orig_pmd;
1773         spinlock_t *ptl;
1774 
1775         tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
1776 
1777         ptl = __pmd_trans_huge_lock(pmd, vma);
1778         if (!ptl)
1779                 return 0;
1780         /*
1781          * For architectures like ppc64 we look at deposited pgtable
1782          * when calling pmdp_huge_get_and_clear. So do the
1783          * pgtable_trans_huge_withdraw after finishing pmdp related
1784          * operations.
1785          */
1786         orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
1787                         tlb->fullmm);
1788         tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1789         if (vma_is_dax(vma)) {
1790                 if (arch_needs_pgtable_deposit())
1791                         zap_deposited_table(tlb->mm, pmd);
1792                 spin_unlock(ptl);
1793                 if (is_huge_zero_pmd(orig_pmd))
1794                         tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
1795         } else if (is_huge_zero_pmd(orig_pmd)) {
1796                 zap_deposited_table(tlb->mm, pmd);
1797                 spin_unlock(ptl);
1798                 tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
1799         } else {
1800                 struct page *page = NULL;
1801                 int flush_needed = 1;
1802 
1803                 if (pmd_present(orig_pmd)) {
1804                         page = pmd_page(orig_pmd);
1805                         page_remove_rmap(page, true);
1806                         VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
1807                         VM_BUG_ON_PAGE(!PageHead(page), page);
1808                 } else if (thp_migration_supported()) {
1809                         swp_entry_t entry;
1810 
1811                         VM_BUG_ON(!is_pmd_migration_entry(orig_pmd));
1812                         entry = pmd_to_swp_entry(orig_pmd);
1813                         page = pfn_to_page(swp_offset(entry));
1814                         flush_needed = 0;
1815                 } else
1816                         WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
1817 
1818                 if (PageAnon(page)) {
1819                         zap_deposited_table(tlb->mm, pmd);
1820                         add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1821                 } else {
1822                         if (arch_needs_pgtable_deposit())
1823                                 zap_deposited_table(tlb->mm, pmd);
1824                         add_mm_counter(tlb->mm, mm_counter_file(page), -HPAGE_PMD_NR);
1825                 }
1826 
1827                 spin_unlock(ptl);
1828                 if (flush_needed)
1829                         tlb_remove_page_size(tlb, page, HPAGE_PMD_SIZE);
1830         }
1831         return 1;
1832 }
1833 
1834 #ifndef pmd_move_must_withdraw
1835 static inline int pmd_move_must_withdraw(spinlock_t *new_pmd_ptl,
1836                                          spinlock_t *old_pmd_ptl,
1837                                          struct vm_area_struct *vma)
1838 {
1839         /*
1840          * With split pmd lock we also need to move preallocated
1841          * PTE page table if new_pmd is on different PMD page table.
1842          *
1843          * We also don't deposit and withdraw tables for file pages.
1844          */
1845         return (new_pmd_ptl != old_pmd_ptl) && vma_is_anonymous(vma);
1846 }
1847 #endif
1848 
1849 static pmd_t move_soft_dirty_pmd(pmd_t pmd)
1850 {
1851 #ifdef CONFIG_MEM_SOFT_DIRTY
1852         if (unlikely(is_pmd_migration_entry(pmd)))
1853                 pmd = pmd_swp_mksoft_dirty(pmd);
1854         else if (pmd_present(pmd))
1855                 pmd = pmd_mksoft_dirty(pmd);
1856 #endif
1857         return pmd;
1858 }
1859 
1860 bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
1861                   unsigned long new_addr, unsigned long old_end,
1862                   pmd_t *old_pmd, pmd_t *new_pmd)
1863 {
1864         spinlock_t *old_ptl, *new_ptl;
1865         pmd_t pmd;
1866         struct mm_struct *mm = vma->vm_mm;
1867         bool force_flush = false;
1868 
1869         if ((old_addr & ~HPAGE_PMD_MASK) ||
1870             (new_addr & ~HPAGE_PMD_MASK) ||
1871             old_end - old_addr < HPAGE_PMD_SIZE)
1872                 return false;
1873 
1874         /*
1875          * The destination pmd shouldn't be established, free_pgtables()
1876          * should have release it.
1877          */
1878         if (WARN_ON(!pmd_none(*new_pmd))) {
1879                 VM_BUG_ON(pmd_trans_huge(*new_pmd));
1880                 return false;
1881         }
1882 
1883         /*
1884          * We don't have to worry about the ordering of src and dst
1885          * ptlocks because exclusive mmap_sem prevents deadlock.
1886          */
1887         old_ptl = __pmd_trans_huge_lock(old_pmd, vma);
1888         if (old_ptl) {
1889                 new_ptl = pmd_lockptr(mm, new_pmd);
1890                 if (new_ptl != old_ptl)
1891                         spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
1892                 pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
1893                 if (pmd_present(pmd))
1894                         force_flush = true;
1895                 VM_BUG_ON(!pmd_none(*new_pmd));
1896 
1897                 if (pmd_move_must_withdraw(new_ptl, old_ptl, vma)) {
1898                         pgtable_t pgtable;
1899                         pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
1900                         pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
1901                 }
1902                 pmd = move_soft_dirty_pmd(pmd);
1903                 set_pmd_at(mm, new_addr, new_pmd, pmd);
1904                 if (force_flush)
1905                         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
1906                 if (new_ptl != old_ptl)
1907                         spin_unlock(new_ptl);
1908                 spin_unlock(old_ptl);
1909                 return true;
1910         }
1911         return false;
1912 }
1913 
1914 /*
1915  * Returns
1916  *  - 0 if PMD could not be locked
1917  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1918  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1919  */
1920 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1921                 unsigned long addr, pgprot_t newprot, int prot_numa)
1922 {
1923         struct mm_struct *mm = vma->vm_mm;
1924         spinlock_t *ptl;
1925         pmd_t entry;
1926         bool preserve_write;
1927         int ret;
1928 
1929         ptl = __pmd_trans_huge_lock(pmd, vma);
1930         if (!ptl)
1931                 return 0;
1932 
1933         preserve_write = prot_numa && pmd_write(*pmd);
1934         ret = 1;
1935 
1936 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
1937         if (is_swap_pmd(*pmd)) {
1938                 swp_entry_t entry = pmd_to_swp_entry(*pmd);
1939 
1940                 VM_BUG_ON(!is_pmd_migration_entry(*pmd));
1941                 if (is_write_migration_entry(entry)) {
1942                         pmd_t newpmd;
1943                         /*
1944                          * A protection check is difficult so
1945                          * just be safe and disable write
1946                          */
1947                         make_migration_entry_read(&entry);
1948                         newpmd = swp_entry_to_pmd(entry);
1949                         if (pmd_swp_soft_dirty(*pmd))
1950                                 newpmd = pmd_swp_mksoft_dirty(newpmd);
1951                         set_pmd_at(mm, addr, pmd, newpmd);
1952                 }
1953                 goto unlock;
1954         }
1955 #endif
1956 
1957         /*
1958          * Avoid trapping faults against the zero page. The read-only
1959          * data is likely to be read-cached on the local CPU and
1960          * local/remote hits to the zero page are not interesting.
1961          */
1962         if (prot_numa && is_huge_zero_pmd(*pmd))
1963                 goto unlock;
1964 
1965         if (prot_numa && pmd_protnone(*pmd))
1966                 goto unlock;
1967 
1968         /*
1969          * In case prot_numa, we are under down_read(mmap_sem). It's critical
1970          * to not clear pmd intermittently to avoid race with MADV_DONTNEED
1971          * which is also under down_read(mmap_sem):
1972          *
1973          *      CPU0:                           CPU1:
1974          *                              change_huge_pmd(prot_numa=1)
1975          *                               pmdp_huge_get_and_clear_notify()
1976          * madvise_dontneed()
1977          *  zap_pmd_range()
1978          *   pmd_trans_huge(*pmd) == 0 (without ptl)
1979          *   // skip the pmd
1980          *                               set_pmd_at();
1981          *                               // pmd is re-established
1982          *
1983          * The race makes MADV_DONTNEED miss the huge pmd and don't clear it
1984          * which may break userspace.
1985          *
1986          * pmdp_invalidate() is required to make sure we don't miss
1987          * dirty/young flags set by hardware.
1988          */
1989         entry = pmdp_invalidate(vma, addr, pmd);
1990 
1991         entry = pmd_modify(entry, newprot);
1992         if (preserve_write)
1993                 entry = pmd_mk_savedwrite(entry);
1994         ret = HPAGE_PMD_NR;
1995         set_pmd_at(mm, addr, pmd, entry);
1996         BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));
1997 unlock:
1998         spin_unlock(ptl);
1999         return ret;
2000 }
2001 
2002 /*
2003  * Returns page table lock pointer if a given pmd maps a thp, NULL otherwise.
2004  *
2005  * Note that if it returns page table lock pointer, this routine returns without
2006  * unlocking page table lock. So callers must unlock it.
2007  */
2008 spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
2009 {
2010         spinlock_t *ptl;
2011         ptl = pmd_lock(vma->vm_mm, pmd);
2012         if (likely(is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) ||
2013                         pmd_devmap(*pmd)))
2014                 return ptl;
2015         spin_unlock(ptl);
2016         return NULL;
2017 }
2018 
2019 /*
2020  * Returns true if a given pud maps a thp, false otherwise.
2021  *
2022  * Note that if it returns true, this routine returns without unlocking page
2023  * table lock. So callers must unlock it.
2024  */
2025 spinlock_t *__pud_trans_huge_lock(pud_t *pud, struct vm_area_struct *vma)
2026 {
2027         spinlock_t *ptl;
2028 
2029         ptl = pud_lock(vma->vm_mm, pud);
2030         if (likely(pud_trans_huge(*pud) || pud_devmap(*pud)))
2031                 return ptl;
2032         spin_unlock(ptl);
2033         return NULL;
2034 }
2035 
2036 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
2037 int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
2038                  pud_t *pud, unsigned long addr)
2039 {
2040         spinlock_t *ptl;
2041 
2042         ptl = __pud_trans_huge_lock(pud, vma);
2043         if (!ptl)
2044                 return 0;
2045         /*
2046          * For architectures like ppc64 we look at deposited pgtable
2047          * when calling pudp_huge_get_and_clear. So do the
2048          * pgtable_trans_huge_withdraw after finishing pudp related
2049          * operations.
2050          */
2051         pudp_huge_get_and_clear_full(tlb->mm, addr, pud, tlb->fullmm);
2052         tlb_remove_pud_tlb_entry(tlb, pud, addr);
2053         if (vma_is_dax(vma)) {
2054                 spin_unlock(ptl);
2055                 /* No zero page support yet */
2056         } else {
2057                 /* No support for anonymous PUD pages yet */
2058                 BUG();
2059         }
2060         return 1;
2061 }
2062 
2063 static void __split_huge_pud_locked(struct vm_area_struct *vma, pud_t *pud,
2064                 unsigned long haddr)
2065 {
2066         VM_BUG_ON(haddr & ~HPAGE_PUD_MASK);
2067         VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
2068         VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PUD_SIZE, vma);
2069         VM_BUG_ON(!pud_trans_huge(*pud) && !pud_devmap(*pud));
2070 
2071         count_vm_event(THP_SPLIT_PUD);
2072 
2073         pudp_huge_clear_flush_notify(vma, haddr, pud);
2074 }
2075 
2076 void __split_huge_pud(struct vm_area_struct *vma, pud_t *pud,
2077                 unsigned long address)
2078 {
2079         spinlock_t *ptl;
2080         struct mmu_notifier_range range;
2081 
2082         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
2083                                 address & HPAGE_PUD_MASK,
2084                                 (address & HPAGE_PUD_MASK) + HPAGE_PUD_SIZE);
2085         mmu_notifier_invalidate_range_start(&range);
2086         ptl = pud_lock(vma->vm_mm, pud);
2087         if (unlikely(!pud_trans_huge(*pud) && !pud_devmap(*pud)))
2088                 goto out;
2089         __split_huge_pud_locked(vma, pud, range.start);
2090 
2091 out:
2092         spin_unlock(ptl);
2093         /*
2094          * No need to double call mmu_notifier->invalidate_range() callback as
2095          * the above pudp_huge_clear_flush_notify() did already call it.
2096          */
2097         mmu_notifier_invalidate_range_only_end(&range);
2098 }
2099 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
2100 
2101 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
2102                 unsigned long haddr, pmd_t *pmd)
2103 {
2104         struct mm_struct *mm = vma->vm_mm;
2105         pgtable_t pgtable;
2106         pmd_t _pmd;
2107         int i;
2108 
2109         /*
2110          * Leave pmd empty until pte is filled note that it is fine to delay
2111          * notification until mmu_notifier_invalidate_range_end() as we are
2112          * replacing a zero pmd write protected page with a zero pte write
2113          * protected page.
2114          *
2115          * See Documentation/vm/mmu_notifier.rst
2116          */
2117         pmdp_huge_clear_flush(vma, haddr, pmd);
2118 
2119         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
2120         pmd_populate(mm, &_pmd, pgtable);
2121 
2122         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
2123                 pte_t *pte, entry;
2124                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
2125                 entry = pte_mkspecial(entry);
2126                 pte = pte_offset_map(&_pmd, haddr);
2127                 VM_BUG_ON(!pte_none(*pte));
2128                 set_pte_at(mm, haddr, pte, entry);
2129                 pte_unmap(pte);
2130         }
2131         smp_wmb(); /* make pte visible before pmd */
2132         pmd_populate(mm, pmd, pgtable);
2133 }
2134 
2135 static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
2136                 unsigned long haddr, bool freeze)
2137 {
2138         struct mm_struct *mm = vma->vm_mm;
2139         struct page *page;
2140         pgtable_t pgtable;
2141         pmd_t old_pmd, _pmd;
2142         bool young, write, soft_dirty, pmd_migration = false;
2143         unsigned long addr;
2144         int i;
2145 
2146         VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
2147         VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
2148         VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
2149         VM_BUG_ON(!is_pmd_migration_entry(*pmd) && !pmd_trans_huge(*pmd)
2150                                 && !pmd_devmap(*pmd));
2151 
2152         count_vm_event(THP_SPLIT_PMD);
2153 
2154         if (!vma_is_anonymous(vma)) {
2155                 _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
2156                 /*
2157                  * We are going to unmap this huge page. So
2158                  * just go ahead and zap it
2159                  */
2160                 if (arch_needs_pgtable_deposit())
2161                         zap_deposited_table(mm, pmd);
2162                 if (vma_is_dax(vma))
2163                         return;
2164                 page = pmd_page(_pmd);
2165                 if (!PageDirty(page) && pmd_dirty(_pmd))
2166                         set_page_dirty(page);
2167                 if (!PageReferenced(page) && pmd_young(_pmd))
2168                         SetPageReferenced(page);
2169                 page_remove_rmap(page, true);
2170                 put_page(page);
2171                 add_mm_counter(mm, mm_counter_file(page), -HPAGE_PMD_NR);
2172                 return;
2173         } else if (is_huge_zero_pmd(*pmd)) {
2174                 /*
2175                  * FIXME: Do we want to invalidate secondary mmu by calling
2176                  * mmu_notifier_invalidate_range() see comments below inside
2177                  * __split_huge_pmd() ?
2178                  *
2179                  * We are going from a zero huge page write protected to zero
2180                  * small page also write protected so it does not seems useful
2181                  * to invalidate secondary mmu at this time.
2182                  */
2183                 return __split_huge_zero_page_pmd(vma, haddr, pmd);
2184         }
2185 
2186         /*
2187          * Up to this point the pmd is present and huge and userland has the
2188          * whole access to the hugepage during the split (which happens in
2189          * place). If we overwrite the pmd with the not-huge version pointing
2190          * to the pte here (which of course we could if all CPUs were bug
2191          * free), userland could trigger a small page size TLB miss on the
2192          * small sized TLB while the hugepage TLB entry is still established in
2193          * the huge TLB. Some CPU doesn't like that.
2194          * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum
2195          * 383 on page 93. Intel should be safe but is also warns that it's
2196          * only safe if the permission and cache attributes of the two entries
2197          * loaded in the two TLB is identical (which should be the case here).
2198          * But it is generally safer to never allow small and huge TLB entries
2199          * for the same virtual address to be loaded simultaneously. So instead
2200          * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the
2201          * current pmd notpresent (atomically because here the pmd_trans_huge
2202          * must remain set at all times on the pmd until the split is complete
2203          * for this pmd), then we flush the SMP TLB and finally we write the
2204          * non-huge version of the pmd entry with pmd_populate.
2205          */
2206         old_pmd = pmdp_invalidate(vma, haddr, pmd);
2207 
2208         pmd_migration = is_pmd_migration_entry(old_pmd);
2209         if (unlikely(pmd_migration)) {
2210                 swp_entry_t entry;
2211 
2212                 entry = pmd_to_swp_entry(old_pmd);
2213                 page = pfn_to_page(swp_offset(entry));
2214                 write = is_write_migration_entry(entry);
2215                 young = false;
2216                 soft_dirty = pmd_swp_soft_dirty(old_pmd);
2217         } else {
2218                 page = pmd_page(old_pmd);
2219                 if (pmd_dirty(old_pmd))
2220                         SetPageDirty(page);
2221                 write = pmd_write(old_pmd);
2222                 young = pmd_young(old_pmd);
2223                 soft_dirty = pmd_soft_dirty(old_pmd);
2224         }
2225         VM_BUG_ON_PAGE(!page_count(page), page);
2226         page_ref_add(page, HPAGE_PMD_NR - 1);
2227 
2228         /*
2229          * Withdraw the table only after we mark the pmd entry invalid.
2230          * This's critical for some architectures (Power).
2231          */
2232         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
2233         pmd_populate(mm, &_pmd, pgtable);
2234 
2235         for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
2236                 pte_t entry, *pte;
2237                 /*
2238                  * Note that NUMA hinting access restrictions are not
2239                  * transferred to avoid any possibility of altering
2240                  * permissions across VMAs.
2241                  */
2242                 if (freeze || pmd_migration) {
2243                         swp_entry_t swp_entry;
2244                         swp_entry = make_migration_entry(page + i, write);
2245                         entry = swp_entry_to_pte(swp_entry);
2246                         if (soft_dirty)
2247                                 entry = pte_swp_mksoft_dirty(entry);
2248                 } else {
2249                         entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
2250                         entry = maybe_mkwrite(entry, vma);
2251                         if (!write)
2252                                 entry = pte_wrprotect(entry);
2253                         if (!young)
2254                                 entry = pte_mkold(entry);
2255                         if (soft_dirty)
2256                                 entry = pte_mksoft_dirty(entry);
2257                 }
2258                 pte = pte_offset_map(&_pmd, addr);
2259                 BUG_ON(!pte_none(*pte));
2260                 set_pte_at(mm, addr, pte, entry);
2261                 atomic_inc(&page[i]._mapcount);
2262                 pte_unmap(pte);
2263         }
2264 
2265         /*
2266          * Set PG_double_map before dropping compound_mapcount to avoid
2267          * false-negative page_mapped().
2268          */
2269         if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
2270                 for (i = 0; i < HPAGE_PMD_NR; i++)
2271                         atomic_inc(&page[i]._mapcount);
2272         }
2273 
2274         if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
2275                 /* Last compound_mapcount is gone. */
2276                 __dec_node_page_state(page, NR_ANON_THPS);
2277                 if (TestClearPageDoubleMap(page)) {
2278                         /* No need in mapcount reference anymore */
2279                         for (i = 0; i < HPAGE_PMD_NR; i++)
2280                                 atomic_dec(&page[i]._mapcount);
2281                 }
2282         }
2283 
2284         smp_wmb(); /* make pte visible before pmd */
2285         pmd_populate(mm, pmd, pgtable);
2286 
2287         if (freeze) {
2288                 for (i = 0; i < HPAGE_PMD_NR; i++) {
2289                         page_remove_rmap(page + i, false);
2290                         put_page(page + i);
2291                 }
2292         }
2293 }
2294 
2295 void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
2296                 unsigned long address, bool freeze, struct page *page)
2297 {
2298         spinlock_t *ptl;
2299         struct mmu_notifier_range range;
2300 
2301         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
2302                                 address & HPAGE_PMD_MASK,
2303                                 (address & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE);
2304         mmu_notifier_invalidate_range_start(&range);
2305         ptl = pmd_lock(vma->vm_mm, pmd);
2306 
2307         /*
2308          * If caller asks to setup a migration entries, we need a page to check
2309          * pmd against. Otherwise we can end up replacing wrong page.
2310          */
2311         VM_BUG_ON(freeze && !page);
2312         if (page && page != pmd_page(*pmd))
2313                 goto out;
2314 
2315         if (pmd_trans_huge(*pmd)) {
2316                 page = pmd_page(*pmd);
2317                 if (PageMlocked(page))
2318                         clear_page_mlock(page);
2319         } else if (!(pmd_devmap(*pmd) || is_pmd_migration_entry(*pmd)))
2320                 goto out;
2321         __split_huge_pmd_locked(vma, pmd, range.start, freeze);
2322 out:
2323         spin_unlock(ptl);
2324         /*
2325          * No need to double call mmu_notifier->invalidate_range() callback.
2326          * They are 3 cases to consider inside __split_huge_pmd_locked():
2327          *  1) pmdp_huge_clear_flush_notify() call invalidate_range() obvious
2328          *  2) __split_huge_zero_page_pmd() read only zero page and any write
2329          *    fault will trigger a flush_notify before pointing to a new page
2330          *    (it is fine if the secondary mmu keeps pointing to the old zero
2331          *    page in the meantime)
2332          *  3) Split a huge pmd into pte pointing to the same page. No need
2333          *     to invalidate secondary tlb entry they are all still valid.
2334          *     any further changes to individual pte will notify. So no need
2335          *     to call mmu_notifier->invalidate_range()
2336          */
2337         mmu_notifier_invalidate_range_only_end(&range);
2338 }
2339 
2340 void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
2341                 bool freeze, struct page *page)
2342 {
2343         pgd_t *pgd;
2344         p4d_t *p4d;
2345         pud_t *pud;
2346         pmd_t *pmd;
2347 
2348         pgd = pgd_offset(vma->vm_mm, address);
2349         if (!pgd_present(*pgd))
2350                 return;
2351 
2352         p4d = p4d_offset(pgd, address);
2353         if (!p4d_present(*p4d))
2354                 return;
2355 
2356         pud = pud_offset(p4d, address);
2357         if (!pud_present(*pud))
2358                 return;
2359 
2360         pmd = pmd_offset(pud, address);
2361 
2362         __split_huge_pmd(vma, pmd, address, freeze, page);
2363 }
2364 
2365 void vma_adjust_trans_huge(struct vm_area_struct *vma,
2366                              unsigned long start,
2367                              unsigned long end,
2368                              long adjust_next)
2369 {
2370         /*
2371          * If the new start address isn't hpage aligned and it could
2372          * previously contain an hugepage: check if we need to split
2373          * an huge pmd.
2374          */
2375         if (start & ~HPAGE_PMD_MASK &&
2376             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
2377             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2378                 split_huge_pmd_address(vma, start, false, NULL);
2379 
2380         /*
2381          * If the new end address isn't hpage aligned and it could
2382          * previously contain an hugepage: check if we need to split
2383          * an huge pmd.
2384          */
2385         if (end & ~HPAGE_PMD_MASK &&
2386             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
2387             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2388                 split_huge_pmd_address(vma, end, false, NULL);
2389 
2390         /*
2391          * If we're also updating the vma->vm_next->vm_start, if the new
2392          * vm_next->vm_start isn't page aligned and it could previously
2393          * contain an hugepage: check if we need to split an huge pmd.
2394          */
2395         if (adjust_next > 0) {
2396                 struct vm_area_struct *next = vma->vm_next;
2397                 unsigned long nstart = next->vm_start;
2398                 nstart += adjust_next << PAGE_SHIFT;
2399                 if (nstart & ~HPAGE_PMD_MASK &&
2400                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
2401                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
2402                         split_huge_pmd_address(next, nstart, false, NULL);
2403         }
2404 }
2405 
2406 static void unmap_page(struct page *page)
2407 {
2408         enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
2409                 TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD;
2410         bool unmap_success;
2411 
2412         VM_BUG_ON_PAGE(!PageHead(page), page);
2413 
2414         if (PageAnon(page))
2415                 ttu_flags |= TTU_SPLIT_FREEZE;
2416 
2417         unmap_success = try_to_unmap(page, ttu_flags);
2418         VM_BUG_ON_PAGE(!unmap_success, page);
2419 }
2420 
2421 static void remap_page(struct page *page)
2422 {
2423         int i;
2424         if (PageTransHuge(page)) {
2425                 remove_migration_ptes(page, page, true);
2426         } else {
2427                 for (i = 0; i < HPAGE_PMD_NR; i++)
2428                         remove_migration_ptes(page + i, page + i, true);
2429         }
2430 }
2431 
2432 static void __split_huge_page_tail(struct page *head, int tail,
2433                 struct lruvec *lruvec, struct list_head *list)
2434 {
2435         struct page *page_tail = head + tail;
2436 
2437         VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
2438 
2439         /*
2440          * Clone page flags before unfreezing refcount.
2441          *
2442          * After successful get_page_unless_zero() might follow flags change,
2443          * for exmaple lock_page() which set PG_waiters.
2444          */
2445         page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
2446         page_tail->flags |= (head->flags &
2447                         ((1L << PG_referenced) |
2448                          (1L << PG_swapbacked) |
2449                          (1L << PG_swapcache) |
2450                          (1L << PG_mlocked) |
2451                          (1L << PG_uptodate) |
2452                          (1L << PG_active) |
2453                          (1L << PG_workingset) |
2454                          (1L << PG_locked) |
2455                          (1L << PG_unevictable) |
2456                          (1L << PG_dirty)));
2457 
2458         /* ->mapping in first tail page is compound_mapcount */
2459         VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
2460                         page_tail);
2461         page_tail->mapping = head->mapping;
2462         page_tail->index = head->index + tail;
2463 
2464         /* Page flags must be visible before we make the page non-compound. */
2465         smp_wmb();
2466 
2467         /*
2468          * Clear PageTail before unfreezing page refcount.
2469          *
2470          * After successful get_page_unless_zero() might follow put_page()
2471          * which needs correct compound_head().
2472          */
2473         clear_compound_head(page_tail);
2474 
2475         /* Finally unfreeze refcount. Additional reference from page cache. */
2476         page_ref_unfreeze(page_tail, 1 + (!PageAnon(head) ||
2477                                           PageSwapCache(head)));
2478 
2479         if (page_is_young(head))
2480                 set_page_young(page_tail);
2481         if (page_is_idle(head))
2482                 set_page_idle(page_tail);
2483 
2484         page_cpupid_xchg_last(page_tail, page_cpupid_last(head));
2485 
2486         /*
2487          * always add to the tail because some iterators expect new
2488          * pages to show after the currently processed elements - e.g.
2489          * migrate_pages
2490          */
2491         lru_add_page_tail(head, page_tail, lruvec, list);
2492 }
2493 
2494 static void __split_huge_page(struct page *page, struct list_head *list,
2495                 pgoff_t end, unsigned long flags)
2496 {
2497         struct page *head = compound_head(page);
2498         pg_data_t *pgdat = page_pgdat(head);
2499         struct lruvec *lruvec;
2500         int i;
2501 
2502         lruvec = mem_cgroup_page_lruvec(head, pgdat);
2503 
2504         /* complete memcg works before add pages to LRU */
2505         mem_cgroup_split_huge_fixup(head);
2506 
2507         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
2508                 __split_huge_page_tail(head, i, lruvec, list);
2509                 /* Some pages can be beyond i_size: drop them from page cache */
2510                 if (head[i].index >= end) {
2511                         ClearPageDirty(head + i);
2512                         __delete_from_page_cache(head + i, NULL);
2513                         if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
2514                                 shmem_uncharge(head->mapping->host, 1);
2515                         put_page(head + i);
2516                 }
2517         }
2518 
2519         ClearPageCompound(head);
2520 
2521         split_page_owner(head, HPAGE_PMD_ORDER);
2522 
2523         /* See comment in __split_huge_page_tail() */
2524         if (PageAnon(head)) {
2525                 /* Additional pin to swap cache */
2526                 if (PageSwapCache(head))
2527                         page_ref_add(head, 2);
2528                 else
2529                         page_ref_inc(head);
2530         } else {
2531                 /* Additional pin to page cache */
2532                 page_ref_add(head, 2);
2533                 xa_unlock(&head->mapping->i_pages);
2534         }
2535 
2536         spin_unlock_irqrestore(&pgdat->lru_lock, flags);
2537 
2538         remap_page(head);
2539 
2540         for (i = 0; i < HPAGE_PMD_NR; i++) {
2541                 struct page *subpage = head + i;
2542                 if (subpage == page)
2543                         continue;
2544                 unlock_page(subpage);
2545 
2546                 /*
2547                  * Subpages may be freed if there wasn't any mapping
2548                  * like if add_to_swap() is running on a lru page that
2549                  * had its mapping zapped. And freeing these pages
2550                  * requires taking the lru_lock so we do the put_page
2551                  * of the tail pages after the split is complete.
2552                  */
2553                 put_page(subpage);
2554         }
2555 }
2556 
2557 int total_mapcount(struct page *page)
2558 {
2559         int i, compound, ret;
2560 
2561         VM_BUG_ON_PAGE(PageTail(page), page);
2562 
2563         if (likely(!PageCompound(page)))
2564                 return atomic_read(&page->_mapcount) + 1;
2565 
2566         compound = compound_mapcount(page);
2567         if (PageHuge(page))
2568                 return compound;
2569         ret = compound;
2570         for (i = 0; i < HPAGE_PMD_NR; i++)
2571                 ret += atomic_read(&page[i]._mapcount) + 1;
2572         /* File pages has compound_mapcount included in _mapcount */
2573         if (!PageAnon(page))
2574                 return ret - compound * HPAGE_PMD_NR;
2575         if (PageDoubleMap(page))
2576                 ret -= HPAGE_PMD_NR;
2577         return ret;
2578 }
2579 
2580 /*
2581  * This calculates accurately how many mappings a transparent hugepage
2582  * has (unlike page_mapcount() which isn't fully accurate). This full
2583  * accuracy is primarily needed to know if copy-on-write faults can
2584  * reuse the page and change the mapping to read-write instead of
2585  * copying them. At the same time this returns the total_mapcount too.
2586  *
2587  * The function returns the highest mapcount any one of the subpages
2588  * has. If the return value is one, even if different processes are
2589  * mapping different subpages of the transparent hugepage, they can
2590  * all reuse it, because each process is reusing a different subpage.
2591  *
2592  * The total_mapcount is instead counting all virtual mappings of the
2593  * subpages. If the total_mapcount is equal to "one", it tells the
2594  * caller all mappings belong to the same "mm" and in turn the
2595  * anon_vma of the transparent hugepage can become the vma->anon_vma
2596  * local one as no other process may be mapping any of the subpages.
2597  *
2598  * It would be more accurate to replace page_mapcount() with
2599  * page_trans_huge_mapcount(), however we only use
2600  * page_trans_huge_mapcount() in the copy-on-write faults where we
2601  * need full accuracy to avoid breaking page pinning, because
2602  * page_trans_huge_mapcount() is slower than page_mapcount().
2603  */
2604 int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
2605 {
2606         int i, ret, _total_mapcount, mapcount;
2607 
2608         /* hugetlbfs shouldn't call it */
2609         VM_BUG_ON_PAGE(PageHuge(page), page);
2610 
2611         if (likely(!PageTransCompound(page))) {
2612                 mapcount = atomic_read(&page->_mapcount) + 1;
2613                 if (total_mapcount)
2614                         *total_mapcount = mapcount;
2615                 return mapcount;
2616         }
2617 
2618         page = compound_head(page);
2619 
2620         _total_mapcount = ret = 0;
2621         for (i = 0; i < HPAGE_PMD_NR; i++) {
2622                 mapcount = atomic_read(&page[i]._mapcount) + 1;
2623                 ret = max(ret, mapcount);
2624                 _total_mapcount += mapcount;
2625         }
2626         if (PageDoubleMap(page)) {
2627                 ret -= 1;
2628                 _total_mapcount -= HPAGE_PMD_NR;
2629         }
2630         mapcount = compound_mapcount(page);
2631         ret += mapcount;
2632         _total_mapcount += mapcount;
2633         if (total_mapcount)
2634                 *total_mapcount = _total_mapcount;
2635         return ret;
2636 }
2637 
2638 /* Racy check whether the huge page can be split */
2639 bool can_split_huge_page(struct page *page, int *pextra_pins)
2640 {
2641         int extra_pins;
2642 
2643         /* Additional pins from page cache */
2644         if (PageAnon(page))
2645                 extra_pins = PageSwapCache(page) ? HPAGE_PMD_NR : 0;
2646         else
2647                 extra_pins = HPAGE_PMD_NR;
2648         if (pextra_pins)
2649                 *pextra_pins = extra_pins;
2650         return total_mapcount(page) == page_count(page) - extra_pins - 1;
2651 }
2652 
2653 /*
2654  * This function splits huge page into normal pages. @page can point to any
2655  * subpage of huge page to split. Split doesn't change the position of @page.
2656  *
2657  * Only caller must hold pin on the @page, otherwise split fails with -EBUSY.
2658  * The huge page must be locked.
2659  *
2660  * If @list is null, tail pages will be added to LRU list, otherwise, to @list.
2661  *
2662  * Both head page and tail pages will inherit mapping, flags, and so on from
2663  * the hugepage.
2664  *
2665  * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if
2666  * they are not mapped.
2667  *
2668  * Returns 0 if the hugepage is split successfully.
2669  * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under
2670  * us.
2671  */
2672 int split_huge_page_to_list(struct page *page, struct list_head *list)
2673 {
2674         struct page *head = compound_head(page);
2675         struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
2676         struct anon_vma *anon_vma = NULL;
2677         struct address_space *mapping = NULL;
2678         int count, mapcount, extra_pins, ret;
2679         bool mlocked;
2680         unsigned long flags;
2681         pgoff_t end;
2682 
2683         VM_BUG_ON_PAGE(is_huge_zero_page(page), page);
2684         VM_BUG_ON_PAGE(!PageLocked(page), page);
2685         VM_BUG_ON_PAGE(!PageCompound(page), page);
2686 
2687         if (PageWriteback(page))
2688                 return -EBUSY;
2689 
2690         if (PageAnon(head)) {
2691                 /*
2692                  * The caller does not necessarily hold an mmap_sem that would
2693                  * prevent the anon_vma disappearing so we first we take a
2694                  * reference to it and then lock the anon_vma for write. This
2695                  * is similar to page_lock_anon_vma_read except the write lock
2696                  * is taken to serialise against parallel split or collapse
2697                  * operations.
2698                  */
2699                 anon_vma = page_get_anon_vma(head);
2700                 if (!anon_vma) {
2701                         ret = -EBUSY;
2702                         goto out;
2703                 }
2704                 end = -1;
2705                 mapping = NULL;
2706                 anon_vma_lock_write(anon_vma);
2707         } else {
2708                 mapping = head->mapping;
2709 
2710                 /* Truncated ? */
2711                 if (!mapping) {
2712                         ret = -EBUSY;
2713                         goto out;
2714                 }
2715 
2716                 anon_vma = NULL;
2717                 i_mmap_lock_read(mapping);
2718 
2719                 /*
2720                  *__split_huge_page() may need to trim off pages beyond EOF:
2721                  * but on 32-bit, i_size_read() takes an irq-unsafe seqlock,
2722                  * which cannot be nested inside the page tree lock. So note
2723                  * end now: i_size itself may be changed at any moment, but
2724                  * head page lock is good enough to serialize the trimming.
2725                  */
2726                 end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
2727         }
2728 
2729         /*
2730          * Racy check if we can split the page, before unmap_page() will
2731          * split PMDs
2732          */
2733         if (!can_split_huge_page(head, &extra_pins)) {
2734                 ret = -EBUSY;
2735                 goto out_unlock;
2736         }
2737 
2738         mlocked = PageMlocked(page);
2739         unmap_page(head);
2740         VM_BUG_ON_PAGE(compound_mapcount(head), head);
2741 
2742         /* Make sure the page is not on per-CPU pagevec as it takes pin */
2743         if (mlocked)
2744                 lru_add_drain();
2745 
2746         /* prevent PageLRU to go away from under us, and freeze lru stats */
2747         spin_lock_irqsave(&pgdata->lru_lock, flags);
2748 
2749         if (mapping) {
2750                 XA_STATE(xas, &mapping->i_pages, page_index(head));
2751 
2752                 /*
2753                  * Check if the head page is present in page cache.
2754                  * We assume all tail are present too, if head is there.
2755                  */
2756                 xa_lock(&mapping->i_pages);
2757                 if (xas_load(&xas) != head)
2758                         goto fail;
2759         }
2760 
2761         /* Prevent deferred_split_scan() touching ->_refcount */
2762         spin_lock(&pgdata->split_queue_lock);
2763         count = page_count(head);
2764         mapcount = total_mapcount(head);
2765         if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
2766                 if (!list_empty(page_deferred_list(head))) {
2767                         pgdata->split_queue_len--;
2768                         list_del(page_deferred_list(head));
2769                 }
2770                 if (mapping)
2771                         __dec_node_page_state(page, NR_SHMEM_THPS);
2772                 spin_unlock(&pgdata->split_queue_lock);
2773                 __split_huge_page(page, list, end, flags);
2774                 if (PageSwapCache(head)) {
2775                         swp_entry_t entry = { .val = page_private(head) };
2776 
2777                         ret = split_swap_cluster(entry);
2778                 } else
2779                         ret = 0;
2780         } else {
2781                 if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
2782                         pr_alert("total_mapcount: %u, page_count(): %u\n",
2783                                         mapcount, count);
2784                         if (PageTail(page))
2785                                 dump_page(head, NULL);
2786                         dump_page(page, "total_mapcount(head) > 0");
2787                         BUG();
2788                 }
2789                 spin_unlock(&pgdata->split_queue_lock);
2790 fail:           if (mapping)
2791                         xa_unlock(&mapping->i_pages);
2792                 spin_unlock_irqrestore(&pgdata->lru_lock, flags);
2793                 remap_page(head);
2794                 ret = -EBUSY;
2795         }
2796 
2797 out_unlock:
2798         if (anon_vma) {
2799                 anon_vma_unlock_write(anon_vma);
2800                 put_anon_vma(anon_vma);
2801         }
2802         if (mapping)
2803                 i_mmap_unlock_read(mapping);
2804 out:
2805         count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
2806         return ret;
2807 }
2808 
2809 void free_transhuge_page(struct page *page)
2810 {
2811         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2812         unsigned long flags;
2813 
2814         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2815         if (!list_empty(page_deferred_list(page))) {
2816                 pgdata->split_queue_len--;
2817                 list_del(page_deferred_list(page));
2818         }
2819         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2820         free_compound_page(page);
2821 }
2822 
2823 void deferred_split_huge_page(struct page *page)
2824 {
2825         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2826         unsigned long flags;
2827 
2828         VM_BUG_ON_PAGE(!PageTransHuge(page), page);
2829 
2830         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2831         if (list_empty(page_deferred_list(page))) {
2832                 count_vm_event(THP_DEFERRED_SPLIT_PAGE);
2833                 list_add_tail(page_deferred_list(page), &pgdata->split_queue);
2834                 pgdata->split_queue_len++;
2835         }
2836         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2837 }
2838 
2839 static unsigned long deferred_split_count(struct shrinker *shrink,
2840                 struct shrink_control *sc)
2841 {
2842         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2843         return READ_ONCE(pgdata->split_queue_len);
2844 }
2845 
2846 static unsigned long deferred_split_scan(struct shrinker *shrink,
2847                 struct shrink_control *sc)
2848 {
2849         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2850         unsigned long flags;
2851         LIST_HEAD(list), *pos, *next;
2852         struct page *page;
2853         int split = 0;
2854 
2855         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2856         /* Take pin on all head pages to avoid freeing them under us */
2857         list_for_each_safe(pos, next, &pgdata->split_queue) {
2858                 page = list_entry((void *)pos, struct page, mapping);
2859                 page = compound_head(page);
2860                 if (get_page_unless_zero(page)) {
2861                         list_move(page_deferred_list(page), &list);
2862                 } else {
2863                         /* We lost race with put_compound_page() */
2864                         list_del_init(page_deferred_list(page));
2865                         pgdata->split_queue_len--;
2866                 }
2867                 if (!--sc->nr_to_scan)
2868                         break;
2869         }
2870         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2871 
2872         list_for_each_safe(pos, next, &list) {
2873                 page = list_entry((void *)pos, struct page, mapping);
2874                 if (!trylock_page(page))
2875                         goto next;
2876                 /* split_huge_page() removes page from list on success */
2877                 if (!split_huge_page(page))
2878                         split++;
2879                 unlock_page(page);
2880 next:
2881                 put_page(page);
2882         }
2883 
2884         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2885         list_splice_tail(&list, &pgdata->split_queue);
2886         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2887 
2888         /*
2889          * Stop shrinker if we didn't split any page, but the queue is empty.
2890          * This can happen if pages were freed under us.
2891          */
2892         if (!split && list_empty(&pgdata->split_queue))
2893                 return SHRINK_STOP;
2894         return split;
2895 }
2896 
2897 static struct shrinker deferred_split_shrinker = {
2898         .count_objects = deferred_split_count,
2899         .scan_objects = deferred_split_scan,
2900         .seeks = DEFAULT_SEEKS,
2901         .flags = SHRINKER_NUMA_AWARE,
2902 };
2903 
2904 #ifdef CONFIG_DEBUG_FS
2905 static int split_huge_pages_set(void *data, u64 val)
2906 {
2907         struct zone *zone;
2908         struct page *page;
2909         unsigned long pfn, max_zone_pfn;
2910         unsigned long total = 0, split = 0;
2911 
2912         if (val != 1)
2913                 return -EINVAL;
2914 
2915         for_each_populated_zone(zone) {
2916                 max_zone_pfn = zone_end_pfn(zone);
2917                 for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
2918                         if (!pfn_valid(pfn))
2919                                 continue;
2920 
2921                         page = pfn_to_page(pfn);
2922                         if (!get_page_unless_zero(page))
2923                                 continue;
2924 
2925                         if (zone != page_zone(page))
2926                                 goto next;
2927 
2928                         if (!PageHead(page) || PageHuge(page) || !PageLRU(page))
2929                                 goto next;
2930 
2931                         total++;
2932                         lock_page(page);
2933                         if (!split_huge_page(page))
2934                                 split++;
2935                         unlock_page(page);
2936 next:
2937                         put_page(page);
2938                 }
2939         }
2940 
2941         pr_info("%lu of %lu THP split\n", split, total);
2942 
2943         return 0;
2944 }
2945 DEFINE_SIMPLE_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
2946                 "%llu\n");
2947 
2948 static int __init split_huge_pages_debugfs(void)
2949 {
2950         debugfs_create_file("split_huge_pages", 0200, NULL, NULL,
2951                             &split_huge_pages_fops);
2952         return 0;
2953 }
2954 late_initcall(split_huge_pages_debugfs);
2955 #endif
2956 
2957 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
2958 void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
2959                 struct page *page)
2960 {
2961         struct vm_area_struct *vma = pvmw->vma;
2962         struct mm_struct *mm = vma->vm_mm;
2963         unsigned long address = pvmw->address;
2964         pmd_t pmdval;
2965         swp_entry_t entry;
2966         pmd_t pmdswp;
2967 
2968         if (!(pvmw->pmd && !pvmw->pte))
2969                 return;
2970 
2971         flush_cache_range(vma, address, address + HPAGE_PMD_SIZE);
2972         pmdval = *pvmw->pmd;
2973         pmdp_invalidate(vma, address, pvmw->pmd);
2974         if (pmd_dirty(pmdval))
2975                 set_page_dirty(page);
2976         entry = make_migration_entry(page, pmd_write(pmdval));
2977         pmdswp = swp_entry_to_pmd(entry);
2978         if (pmd_soft_dirty(pmdval))
2979                 pmdswp = pmd_swp_mksoft_dirty(pmdswp);
2980         set_pmd_at(mm, address, pvmw->pmd, pmdswp);
2981         page_remove_rmap(page, true);
2982         put_page(page);
2983 }
2984 
2985 void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
2986 {
2987         struct vm_area_struct *vma = pvmw->vma;
2988         struct mm_struct *mm = vma->vm_mm;
2989         unsigned long address = pvmw->address;
2990         unsigned long mmun_start = address & HPAGE_PMD_MASK;
2991         pmd_t pmde;
2992         swp_entry_t entry;
2993 
2994         if (!(pvmw->pmd && !pvmw->pte))
2995                 return;
2996 
2997         entry = pmd_to_swp_entry(*pvmw->pmd);
2998         get_page(new);
2999         pmde = pmd_mkold(mk_huge_pmd(new, vma->vm_page_prot));
3000         if (pmd_swp_soft_dirty(*pvmw->pmd))
3001                 pmde = pmd_mksoft_dirty(pmde);
3002         if (is_write_migration_entry(entry))
3003                 pmde = maybe_pmd_mkwrite(pmde, vma);
3004 
3005         flush_cache_range(vma, mmun_start, mmun_start + HPAGE_PMD_SIZE);
3006         if (PageAnon(new))
3007                 page_add_anon_rmap(new, vma, mmun_start, true);
3008         else
3009                 page_add_file_rmap(new, true);
3010         set_pmd_at(mm, mmun_start, pvmw->pmd, pmde);
3011         if ((vma->vm_flags & VM_LOCKED) && !PageDoubleMap(new))
3012                 mlock_vma_page(new);
3013         update_mmu_cache_pmd(vma, address, pvmw->pmd);
3014 }
3015 #endif
3016 

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