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TOMOYO Linux Cross Reference
Linux/mm/huge_memory.c

Version: ~ [ linux-5.4-rc3 ] ~ [ linux-5.3.6 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.79 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.149 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.196 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.196 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.140 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.75 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-3.9.11 ] ~ [ linux-3.8.13 ] ~ [ linux-3.7.10 ] ~ [ linux-3.6.11 ] ~ [ linux-3.5.7 ] ~ [ linux-3.4.113 ] ~ [ linux-3.3.8 ] ~ [ linux-3.2.102 ] ~ [ linux-3.1.10 ] ~ [ linux-3.0.101 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  1 /*
  2  *  Copyright (C) 2009  Red Hat, Inc.
  3  *
  4  *  This work is licensed under the terms of the GNU GPL, version 2. See
  5  *  the COPYING file in the top-level directory.
  6  */
  7 
  8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  9 
 10 #include <linux/mm.h>
 11 #include <linux/sched.h>
 12 #include <linux/sched/coredump.h>
 13 #include <linux/sched/numa_balancing.h>
 14 #include <linux/highmem.h>
 15 #include <linux/hugetlb.h>
 16 #include <linux/mmu_notifier.h>
 17 #include <linux/rmap.h>
 18 #include <linux/swap.h>
 19 #include <linux/shrinker.h>
 20 #include <linux/mm_inline.h>
 21 #include <linux/swapops.h>
 22 #include <linux/dax.h>
 23 #include <linux/khugepaged.h>
 24 #include <linux/freezer.h>
 25 #include <linux/pfn_t.h>
 26 #include <linux/mman.h>
 27 #include <linux/memremap.h>
 28 #include <linux/pagemap.h>
 29 #include <linux/debugfs.h>
 30 #include <linux/migrate.h>
 31 #include <linux/hashtable.h>
 32 #include <linux/userfaultfd_k.h>
 33 #include <linux/page_idle.h>
 34 #include <linux/shmem_fs.h>
 35 
 36 #include <asm/tlb.h>
 37 #include <asm/pgalloc.h>
 38 #include "internal.h"
 39 
 40 /*
 41  * By default transparent hugepage support is disabled in order that avoid
 42  * to risk increase the memory footprint of applications without a guaranteed
 43  * benefit. When transparent hugepage support is enabled, is for all mappings,
 44  * and khugepaged scans all mappings.
 45  * Defrag is invoked by khugepaged hugepage allocations and by page faults
 46  * for all hugepage allocations.
 47  */
 48 unsigned long transparent_hugepage_flags __read_mostly =
 49 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
 50         (1<<TRANSPARENT_HUGEPAGE_FLAG)|
 51 #endif
 52 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
 53         (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
 54 #endif
 55         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG)|
 56         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
 57         (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 58 
 59 static struct shrinker deferred_split_shrinker;
 60 
 61 static atomic_t huge_zero_refcount;
 62 struct page *huge_zero_page __read_mostly;
 63 
 64 static struct page *get_huge_zero_page(void)
 65 {
 66         struct page *zero_page;
 67 retry:
 68         if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
 69                 return READ_ONCE(huge_zero_page);
 70 
 71         zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
 72                         HPAGE_PMD_ORDER);
 73         if (!zero_page) {
 74                 count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
 75                 return NULL;
 76         }
 77         count_vm_event(THP_ZERO_PAGE_ALLOC);
 78         preempt_disable();
 79         if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
 80                 preempt_enable();
 81                 __free_pages(zero_page, compound_order(zero_page));
 82                 goto retry;
 83         }
 84 
 85         /* We take additional reference here. It will be put back by shrinker */
 86         atomic_set(&huge_zero_refcount, 2);
 87         preempt_enable();
 88         return READ_ONCE(huge_zero_page);
 89 }
 90 
 91 static void put_huge_zero_page(void)
 92 {
 93         /*
 94          * Counter should never go to zero here. Only shrinker can put
 95          * last reference.
 96          */
 97         BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
 98 }
 99 
100 struct page *mm_get_huge_zero_page(struct mm_struct *mm)
101 {
102         if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
103                 return READ_ONCE(huge_zero_page);
104 
105         if (!get_huge_zero_page())
106                 return NULL;
107 
108         if (test_and_set_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
109                 put_huge_zero_page();
110 
111         return READ_ONCE(huge_zero_page);
112 }
113 
114 void mm_put_huge_zero_page(struct mm_struct *mm)
115 {
116         if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
117                 put_huge_zero_page();
118 }
119 
120 static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
121                                         struct shrink_control *sc)
122 {
123         /* we can free zero page only if last reference remains */
124         return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
125 }
126 
127 static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
128                                        struct shrink_control *sc)
129 {
130         if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
131                 struct page *zero_page = xchg(&huge_zero_page, NULL);
132                 BUG_ON(zero_page == NULL);
133                 __free_pages(zero_page, compound_order(zero_page));
134                 return HPAGE_PMD_NR;
135         }
136 
137         return 0;
138 }
139 
140 static struct shrinker huge_zero_page_shrinker = {
141         .count_objects = shrink_huge_zero_page_count,
142         .scan_objects = shrink_huge_zero_page_scan,
143         .seeks = DEFAULT_SEEKS,
144 };
145 
146 #ifdef CONFIG_SYSFS
147 static ssize_t enabled_show(struct kobject *kobj,
148                             struct kobj_attribute *attr, char *buf)
149 {
150         if (test_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags))
151                 return sprintf(buf, "[always] madvise never\n");
152         else if (test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags))
153                 return sprintf(buf, "always [madvise] never\n");
154         else
155                 return sprintf(buf, "always madvise [never]\n");
156 }
157 
158 static ssize_t enabled_store(struct kobject *kobj,
159                              struct kobj_attribute *attr,
160                              const char *buf, size_t count)
161 {
162         ssize_t ret = count;
163 
164         if (!memcmp("always", buf,
165                     min(sizeof("always")-1, count))) {
166                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
167                 set_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
168         } else if (!memcmp("madvise", buf,
169                            min(sizeof("madvise")-1, count))) {
170                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
171                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
172         } else if (!memcmp("never", buf,
173                            min(sizeof("never")-1, count))) {
174                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
175                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
176         } else
177                 ret = -EINVAL;
178 
179         if (ret > 0) {
180                 int err = start_stop_khugepaged();
181                 if (err)
182                         ret = err;
183         }
184         return ret;
185 }
186 static struct kobj_attribute enabled_attr =
187         __ATTR(enabled, 0644, enabled_show, enabled_store);
188 
189 ssize_t single_hugepage_flag_show(struct kobject *kobj,
190                                 struct kobj_attribute *attr, char *buf,
191                                 enum transparent_hugepage_flag flag)
192 {
193         return sprintf(buf, "%d\n",
194                        !!test_bit(flag, &transparent_hugepage_flags));
195 }
196 
197 ssize_t single_hugepage_flag_store(struct kobject *kobj,
198                                  struct kobj_attribute *attr,
199                                  const char *buf, size_t count,
200                                  enum transparent_hugepage_flag flag)
201 {
202         unsigned long value;
203         int ret;
204 
205         ret = kstrtoul(buf, 10, &value);
206         if (ret < 0)
207                 return ret;
208         if (value > 1)
209                 return -EINVAL;
210 
211         if (value)
212                 set_bit(flag, &transparent_hugepage_flags);
213         else
214                 clear_bit(flag, &transparent_hugepage_flags);
215 
216         return count;
217 }
218 
219 static ssize_t defrag_show(struct kobject *kobj,
220                            struct kobj_attribute *attr, char *buf)
221 {
222         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
223                 return sprintf(buf, "[always] defer defer+madvise madvise never\n");
224         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
225                 return sprintf(buf, "always [defer] defer+madvise madvise never\n");
226         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags))
227                 return sprintf(buf, "always defer [defer+madvise] madvise never\n");
228         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
229                 return sprintf(buf, "always defer defer+madvise [madvise] never\n");
230         return sprintf(buf, "always defer defer+madvise madvise [never]\n");
231 }
232 
233 static ssize_t defrag_store(struct kobject *kobj,
234                             struct kobj_attribute *attr,
235                             const char *buf, size_t count)
236 {
237         if (!memcmp("always", buf,
238                     min(sizeof("always")-1, count))) {
239                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
240                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
241                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
242                 set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
243         } else if (!memcmp("defer+madvise", buf,
244                     min(sizeof("defer+madvise")-1, count))) {
245                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
246                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
247                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
248                 set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
249         } else if (!memcmp("defer", buf,
250                     min(sizeof("defer")-1, count))) {
251                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
252                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
253                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
254                 set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
255         } else if (!memcmp("madvise", buf,
256                            min(sizeof("madvise")-1, count))) {
257                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
258                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
259                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
260                 set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
261         } else if (!memcmp("never", buf,
262                            min(sizeof("never")-1, count))) {
263                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
264                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
265                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
266                 clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
267         } else
268                 return -EINVAL;
269 
270         return count;
271 }
272 static struct kobj_attribute defrag_attr =
273         __ATTR(defrag, 0644, defrag_show, defrag_store);
274 
275 static ssize_t use_zero_page_show(struct kobject *kobj,
276                 struct kobj_attribute *attr, char *buf)
277 {
278         return single_hugepage_flag_show(kobj, attr, buf,
279                                 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
280 }
281 static ssize_t use_zero_page_store(struct kobject *kobj,
282                 struct kobj_attribute *attr, const char *buf, size_t count)
283 {
284         return single_hugepage_flag_store(kobj, attr, buf, count,
285                                  TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
286 }
287 static struct kobj_attribute use_zero_page_attr =
288         __ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
289 
290 static ssize_t hpage_pmd_size_show(struct kobject *kobj,
291                 struct kobj_attribute *attr, char *buf)
292 {
293         return sprintf(buf, "%lu\n", HPAGE_PMD_SIZE);
294 }
295 static struct kobj_attribute hpage_pmd_size_attr =
296         __ATTR_RO(hpage_pmd_size);
297 
298 #ifdef CONFIG_DEBUG_VM
299 static ssize_t debug_cow_show(struct kobject *kobj,
300                                 struct kobj_attribute *attr, char *buf)
301 {
302         return single_hugepage_flag_show(kobj, attr, buf,
303                                 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
304 }
305 static ssize_t debug_cow_store(struct kobject *kobj,
306                                struct kobj_attribute *attr,
307                                const char *buf, size_t count)
308 {
309         return single_hugepage_flag_store(kobj, attr, buf, count,
310                                  TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
311 }
312 static struct kobj_attribute debug_cow_attr =
313         __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
314 #endif /* CONFIG_DEBUG_VM */
315 
316 static struct attribute *hugepage_attr[] = {
317         &enabled_attr.attr,
318         &defrag_attr.attr,
319         &use_zero_page_attr.attr,
320         &hpage_pmd_size_attr.attr,
321 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
322         &shmem_enabled_attr.attr,
323 #endif
324 #ifdef CONFIG_DEBUG_VM
325         &debug_cow_attr.attr,
326 #endif
327         NULL,
328 };
329 
330 static struct attribute_group hugepage_attr_group = {
331         .attrs = hugepage_attr,
332 };
333 
334 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
335 {
336         int err;
337 
338         *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
339         if (unlikely(!*hugepage_kobj)) {
340                 pr_err("failed to create transparent hugepage kobject\n");
341                 return -ENOMEM;
342         }
343 
344         err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
345         if (err) {
346                 pr_err("failed to register transparent hugepage group\n");
347                 goto delete_obj;
348         }
349 
350         err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
351         if (err) {
352                 pr_err("failed to register transparent hugepage group\n");
353                 goto remove_hp_group;
354         }
355 
356         return 0;
357 
358 remove_hp_group:
359         sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
360 delete_obj:
361         kobject_put(*hugepage_kobj);
362         return err;
363 }
364 
365 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
366 {
367         sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
368         sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
369         kobject_put(hugepage_kobj);
370 }
371 #else
372 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
373 {
374         return 0;
375 }
376 
377 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
378 {
379 }
380 #endif /* CONFIG_SYSFS */
381 
382 static int __init hugepage_init(void)
383 {
384         int err;
385         struct kobject *hugepage_kobj;
386 
387         if (!has_transparent_hugepage()) {
388                 transparent_hugepage_flags = 0;
389                 return -EINVAL;
390         }
391 
392         /*
393          * hugepages can't be allocated by the buddy allocator
394          */
395         MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER >= MAX_ORDER);
396         /*
397          * we use page->mapping and page->index in second tail page
398          * as list_head: assuming THP order >= 2
399          */
400         MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER < 2);
401 
402         err = hugepage_init_sysfs(&hugepage_kobj);
403         if (err)
404                 goto err_sysfs;
405 
406         err = khugepaged_init();
407         if (err)
408                 goto err_slab;
409 
410         err = register_shrinker(&huge_zero_page_shrinker);
411         if (err)
412                 goto err_hzp_shrinker;
413         err = register_shrinker(&deferred_split_shrinker);
414         if (err)
415                 goto err_split_shrinker;
416 
417         /*
418          * By default disable transparent hugepages on smaller systems,
419          * where the extra memory used could hurt more than TLB overhead
420          * is likely to save.  The admin can still enable it through /sys.
421          */
422         if (totalram_pages < (512 << (20 - PAGE_SHIFT))) {
423                 transparent_hugepage_flags = 0;
424                 return 0;
425         }
426 
427         err = start_stop_khugepaged();
428         if (err)
429                 goto err_khugepaged;
430 
431         return 0;
432 err_khugepaged:
433         unregister_shrinker(&deferred_split_shrinker);
434 err_split_shrinker:
435         unregister_shrinker(&huge_zero_page_shrinker);
436 err_hzp_shrinker:
437         khugepaged_destroy();
438 err_slab:
439         hugepage_exit_sysfs(hugepage_kobj);
440 err_sysfs:
441         return err;
442 }
443 subsys_initcall(hugepage_init);
444 
445 static int __init setup_transparent_hugepage(char *str)
446 {
447         int ret = 0;
448         if (!str)
449                 goto out;
450         if (!strcmp(str, "always")) {
451                 set_bit(TRANSPARENT_HUGEPAGE_FLAG,
452                         &transparent_hugepage_flags);
453                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
454                           &transparent_hugepage_flags);
455                 ret = 1;
456         } else if (!strcmp(str, "madvise")) {
457                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
458                           &transparent_hugepage_flags);
459                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
460                         &transparent_hugepage_flags);
461                 ret = 1;
462         } else if (!strcmp(str, "never")) {
463                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
464                           &transparent_hugepage_flags);
465                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
466                           &transparent_hugepage_flags);
467                 ret = 1;
468         }
469 out:
470         if (!ret)
471                 pr_warn("transparent_hugepage= cannot parse, ignored\n");
472         return ret;
473 }
474 __setup("transparent_hugepage=", setup_transparent_hugepage);
475 
476 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
477 {
478         if (likely(vma->vm_flags & VM_WRITE))
479                 pmd = pmd_mkwrite(pmd);
480         return pmd;
481 }
482 
483 static inline struct list_head *page_deferred_list(struct page *page)
484 {
485         /*
486          * ->lru in the tail pages is occupied by compound_head.
487          * Let's use ->mapping + ->index in the second tail page as list_head.
488          */
489         return (struct list_head *)&page[2].mapping;
490 }
491 
492 void prep_transhuge_page(struct page *page)
493 {
494         /*
495          * we use page->mapping and page->indexlru in second tail page
496          * as list_head: assuming THP order >= 2
497          */
498 
499         INIT_LIST_HEAD(page_deferred_list(page));
500         set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
501 }
502 
503 unsigned long __thp_get_unmapped_area(struct file *filp, unsigned long len,
504                 loff_t off, unsigned long flags, unsigned long size)
505 {
506         unsigned long addr;
507         loff_t off_end = off + len;
508         loff_t off_align = round_up(off, size);
509         unsigned long len_pad;
510 
511         if (off_end <= off_align || (off_end - off_align) < size)
512                 return 0;
513 
514         len_pad = len + size;
515         if (len_pad < len || (off + len_pad) < off)
516                 return 0;
517 
518         addr = current->mm->get_unmapped_area(filp, 0, len_pad,
519                                               off >> PAGE_SHIFT, flags);
520         if (IS_ERR_VALUE(addr))
521                 return 0;
522 
523         addr += (off - addr) & (size - 1);
524         return addr;
525 }
526 
527 unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
528                 unsigned long len, unsigned long pgoff, unsigned long flags)
529 {
530         loff_t off = (loff_t)pgoff << PAGE_SHIFT;
531 
532         if (addr)
533                 goto out;
534         if (!IS_DAX(filp->f_mapping->host) || !IS_ENABLED(CONFIG_FS_DAX_PMD))
535                 goto out;
536 
537         addr = __thp_get_unmapped_area(filp, len, off, flags, PMD_SIZE);
538         if (addr)
539                 return addr;
540 
541  out:
542         return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags);
543 }
544 EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
545 
546 static int __do_huge_pmd_anonymous_page(struct vm_fault *vmf, struct page *page,
547                 gfp_t gfp)
548 {
549         struct vm_area_struct *vma = vmf->vma;
550         struct mem_cgroup *memcg;
551         pgtable_t pgtable;
552         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
553 
554         VM_BUG_ON_PAGE(!PageCompound(page), page);
555 
556         if (mem_cgroup_try_charge(page, vma->vm_mm, gfp, &memcg, true)) {
557                 put_page(page);
558                 count_vm_event(THP_FAULT_FALLBACK);
559                 return VM_FAULT_FALLBACK;
560         }
561 
562         pgtable = pte_alloc_one(vma->vm_mm, haddr);
563         if (unlikely(!pgtable)) {
564                 mem_cgroup_cancel_charge(page, memcg, true);
565                 put_page(page);
566                 return VM_FAULT_OOM;
567         }
568 
569         clear_huge_page(page, haddr, HPAGE_PMD_NR);
570         /*
571          * The memory barrier inside __SetPageUptodate makes sure that
572          * clear_huge_page writes become visible before the set_pmd_at()
573          * write.
574          */
575         __SetPageUptodate(page);
576 
577         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
578         if (unlikely(!pmd_none(*vmf->pmd))) {
579                 spin_unlock(vmf->ptl);
580                 mem_cgroup_cancel_charge(page, memcg, true);
581                 put_page(page);
582                 pte_free(vma->vm_mm, pgtable);
583         } else {
584                 pmd_t entry;
585 
586                 /* Deliver the page fault to userland */
587                 if (userfaultfd_missing(vma)) {
588                         int ret;
589 
590                         spin_unlock(vmf->ptl);
591                         mem_cgroup_cancel_charge(page, memcg, true);
592                         put_page(page);
593                         pte_free(vma->vm_mm, pgtable);
594                         ret = handle_userfault(vmf, VM_UFFD_MISSING);
595                         VM_BUG_ON(ret & VM_FAULT_FALLBACK);
596                         return ret;
597                 }
598 
599                 entry = mk_huge_pmd(page, vma->vm_page_prot);
600                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
601                 page_add_new_anon_rmap(page, vma, haddr, true);
602                 mem_cgroup_commit_charge(page, memcg, false, true);
603                 lru_cache_add_active_or_unevictable(page, vma);
604                 pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
605                 set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
606                 add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
607                 atomic_long_inc(&vma->vm_mm->nr_ptes);
608                 spin_unlock(vmf->ptl);
609                 count_vm_event(THP_FAULT_ALLOC);
610         }
611 
612         return 0;
613 }
614 
615 /*
616  * always: directly stall for all thp allocations
617  * defer: wake kswapd and fail if not immediately available
618  * defer+madvise: wake kswapd and directly stall for MADV_HUGEPAGE, otherwise
619  *                fail if not immediately available
620  * madvise: directly stall for MADV_HUGEPAGE, otherwise fail if not immediately
621  *          available
622  * never: never stall for any thp allocation
623  */
624 static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
625 {
626         const bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
627 
628         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
629                 return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY);
630         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
631                 return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM;
632         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags))
633                 return GFP_TRANSHUGE_LIGHT | (vma_madvised ? __GFP_DIRECT_RECLAIM :
634                                                              __GFP_KSWAPD_RECLAIM);
635         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
636                 return GFP_TRANSHUGE_LIGHT | (vma_madvised ? __GFP_DIRECT_RECLAIM :
637                                                              0);
638         return GFP_TRANSHUGE_LIGHT;
639 }
640 
641 /* Caller must hold page table lock. */
642 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
643                 struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
644                 struct page *zero_page)
645 {
646         pmd_t entry;
647         if (!pmd_none(*pmd))
648                 return false;
649         entry = mk_pmd(zero_page, vma->vm_page_prot);
650         entry = pmd_mkhuge(entry);
651         if (pgtable)
652                 pgtable_trans_huge_deposit(mm, pmd, pgtable);
653         set_pmd_at(mm, haddr, pmd, entry);
654         atomic_long_inc(&mm->nr_ptes);
655         return true;
656 }
657 
658 int do_huge_pmd_anonymous_page(struct vm_fault *vmf)
659 {
660         struct vm_area_struct *vma = vmf->vma;
661         gfp_t gfp;
662         struct page *page;
663         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
664 
665         if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
666                 return VM_FAULT_FALLBACK;
667         if (unlikely(anon_vma_prepare(vma)))
668                 return VM_FAULT_OOM;
669         if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
670                 return VM_FAULT_OOM;
671         if (!(vmf->flags & FAULT_FLAG_WRITE) &&
672                         !mm_forbids_zeropage(vma->vm_mm) &&
673                         transparent_hugepage_use_zero_page()) {
674                 pgtable_t pgtable;
675                 struct page *zero_page;
676                 bool set;
677                 int ret;
678                 pgtable = pte_alloc_one(vma->vm_mm, haddr);
679                 if (unlikely(!pgtable))
680                         return VM_FAULT_OOM;
681                 zero_page = mm_get_huge_zero_page(vma->vm_mm);
682                 if (unlikely(!zero_page)) {
683                         pte_free(vma->vm_mm, pgtable);
684                         count_vm_event(THP_FAULT_FALLBACK);
685                         return VM_FAULT_FALLBACK;
686                 }
687                 vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
688                 ret = 0;
689                 set = false;
690                 if (pmd_none(*vmf->pmd)) {
691                         if (userfaultfd_missing(vma)) {
692                                 spin_unlock(vmf->ptl);
693                                 ret = handle_userfault(vmf, VM_UFFD_MISSING);
694                                 VM_BUG_ON(ret & VM_FAULT_FALLBACK);
695                         } else {
696                                 set_huge_zero_page(pgtable, vma->vm_mm, vma,
697                                                    haddr, vmf->pmd, zero_page);
698                                 spin_unlock(vmf->ptl);
699                                 set = true;
700                         }
701                 } else
702                         spin_unlock(vmf->ptl);
703                 if (!set)
704                         pte_free(vma->vm_mm, pgtable);
705                 return ret;
706         }
707         gfp = alloc_hugepage_direct_gfpmask(vma);
708         page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
709         if (unlikely(!page)) {
710                 count_vm_event(THP_FAULT_FALLBACK);
711                 return VM_FAULT_FALLBACK;
712         }
713         prep_transhuge_page(page);
714         return __do_huge_pmd_anonymous_page(vmf, page, gfp);
715 }
716 
717 static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
718                 pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write)
719 {
720         struct mm_struct *mm = vma->vm_mm;
721         pmd_t entry;
722         spinlock_t *ptl;
723 
724         ptl = pmd_lock(mm, pmd);
725         entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
726         if (pfn_t_devmap(pfn))
727                 entry = pmd_mkdevmap(entry);
728         if (write) {
729                 entry = pmd_mkyoung(pmd_mkdirty(entry));
730                 entry = maybe_pmd_mkwrite(entry, vma);
731         }
732         set_pmd_at(mm, addr, pmd, entry);
733         update_mmu_cache_pmd(vma, addr, pmd);
734         spin_unlock(ptl);
735 }
736 
737 int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
738                         pmd_t *pmd, pfn_t pfn, bool write)
739 {
740         pgprot_t pgprot = vma->vm_page_prot;
741         /*
742          * If we had pmd_special, we could avoid all these restrictions,
743          * but we need to be consistent with PTEs and architectures that
744          * can't support a 'special' bit.
745          */
746         BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
747         BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
748                                                 (VM_PFNMAP|VM_MIXEDMAP));
749         BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
750         BUG_ON(!pfn_t_devmap(pfn));
751 
752         if (addr < vma->vm_start || addr >= vma->vm_end)
753                 return VM_FAULT_SIGBUS;
754 
755         track_pfn_insert(vma, &pgprot, pfn);
756 
757         insert_pfn_pmd(vma, addr, pmd, pfn, pgprot, write);
758         return VM_FAULT_NOPAGE;
759 }
760 EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd);
761 
762 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
763 static pud_t maybe_pud_mkwrite(pud_t pud, struct vm_area_struct *vma)
764 {
765         if (likely(vma->vm_flags & VM_WRITE))
766                 pud = pud_mkwrite(pud);
767         return pud;
768 }
769 
770 static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
771                 pud_t *pud, pfn_t pfn, pgprot_t prot, bool write)
772 {
773         struct mm_struct *mm = vma->vm_mm;
774         pud_t entry;
775         spinlock_t *ptl;
776 
777         ptl = pud_lock(mm, pud);
778         entry = pud_mkhuge(pfn_t_pud(pfn, prot));
779         if (pfn_t_devmap(pfn))
780                 entry = pud_mkdevmap(entry);
781         if (write) {
782                 entry = pud_mkyoung(pud_mkdirty(entry));
783                 entry = maybe_pud_mkwrite(entry, vma);
784         }
785         set_pud_at(mm, addr, pud, entry);
786         update_mmu_cache_pud(vma, addr, pud);
787         spin_unlock(ptl);
788 }
789 
790 int vmf_insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
791                         pud_t *pud, pfn_t pfn, bool write)
792 {
793         pgprot_t pgprot = vma->vm_page_prot;
794         /*
795          * If we had pud_special, we could avoid all these restrictions,
796          * but we need to be consistent with PTEs and architectures that
797          * can't support a 'special' bit.
798          */
799         BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
800         BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
801                                                 (VM_PFNMAP|VM_MIXEDMAP));
802         BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
803         BUG_ON(!pfn_t_devmap(pfn));
804 
805         if (addr < vma->vm_start || addr >= vma->vm_end)
806                 return VM_FAULT_SIGBUS;
807 
808         track_pfn_insert(vma, &pgprot, pfn);
809 
810         insert_pfn_pud(vma, addr, pud, pfn, pgprot, write);
811         return VM_FAULT_NOPAGE;
812 }
813 EXPORT_SYMBOL_GPL(vmf_insert_pfn_pud);
814 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
815 
816 static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
817                 pmd_t *pmd)
818 {
819         pmd_t _pmd;
820 
821         /*
822          * We should set the dirty bit only for FOLL_WRITE but for now
823          * the dirty bit in the pmd is meaningless.  And if the dirty
824          * bit will become meaningful and we'll only set it with
825          * FOLL_WRITE, an atomic set_bit will be required on the pmd to
826          * set the young bit, instead of the current set_pmd_at.
827          */
828         _pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
829         if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
830                                 pmd, _pmd,  1))
831                 update_mmu_cache_pmd(vma, addr, pmd);
832 }
833 
834 struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
835                 pmd_t *pmd, int flags)
836 {
837         unsigned long pfn = pmd_pfn(*pmd);
838         struct mm_struct *mm = vma->vm_mm;
839         struct dev_pagemap *pgmap;
840         struct page *page;
841 
842         assert_spin_locked(pmd_lockptr(mm, pmd));
843 
844         /*
845          * When we COW a devmap PMD entry, we split it into PTEs, so we should
846          * not be in this function with `flags & FOLL_COW` set.
847          */
848         WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");
849 
850         if (flags & FOLL_WRITE && !pmd_write(*pmd))
851                 return NULL;
852 
853         if (pmd_present(*pmd) && pmd_devmap(*pmd))
854                 /* pass */;
855         else
856                 return NULL;
857 
858         if (flags & FOLL_TOUCH)
859                 touch_pmd(vma, addr, pmd);
860 
861         /*
862          * device mapped pages can only be returned if the
863          * caller will manage the page reference count.
864          */
865         if (!(flags & FOLL_GET))
866                 return ERR_PTR(-EEXIST);
867 
868         pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
869         pgmap = get_dev_pagemap(pfn, NULL);
870         if (!pgmap)
871                 return ERR_PTR(-EFAULT);
872         page = pfn_to_page(pfn);
873         get_page(page);
874         put_dev_pagemap(pgmap);
875 
876         return page;
877 }
878 
879 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
880                   pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
881                   struct vm_area_struct *vma)
882 {
883         spinlock_t *dst_ptl, *src_ptl;
884         struct page *src_page;
885         pmd_t pmd;
886         pgtable_t pgtable = NULL;
887         int ret = -ENOMEM;
888 
889         /* Skip if can be re-fill on fault */
890         if (!vma_is_anonymous(vma))
891                 return 0;
892 
893         pgtable = pte_alloc_one(dst_mm, addr);
894         if (unlikely(!pgtable))
895                 goto out;
896 
897         dst_ptl = pmd_lock(dst_mm, dst_pmd);
898         src_ptl = pmd_lockptr(src_mm, src_pmd);
899         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
900 
901         ret = -EAGAIN;
902         pmd = *src_pmd;
903         if (unlikely(!pmd_trans_huge(pmd))) {
904                 pte_free(dst_mm, pgtable);
905                 goto out_unlock;
906         }
907         /*
908          * When page table lock is held, the huge zero pmd should not be
909          * under splitting since we don't split the page itself, only pmd to
910          * a page table.
911          */
912         if (is_huge_zero_pmd(pmd)) {
913                 struct page *zero_page;
914                 /*
915                  * get_huge_zero_page() will never allocate a new page here,
916                  * since we already have a zero page to copy. It just takes a
917                  * reference.
918                  */
919                 zero_page = mm_get_huge_zero_page(dst_mm);
920                 set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
921                                 zero_page);
922                 ret = 0;
923                 goto out_unlock;
924         }
925 
926         src_page = pmd_page(pmd);
927         VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
928         get_page(src_page);
929         page_dup_rmap(src_page, true);
930         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
931         atomic_long_inc(&dst_mm->nr_ptes);
932         pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
933 
934         pmdp_set_wrprotect(src_mm, addr, src_pmd);
935         pmd = pmd_mkold(pmd_wrprotect(pmd));
936         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
937 
938         ret = 0;
939 out_unlock:
940         spin_unlock(src_ptl);
941         spin_unlock(dst_ptl);
942 out:
943         return ret;
944 }
945 
946 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
947 static void touch_pud(struct vm_area_struct *vma, unsigned long addr,
948                 pud_t *pud)
949 {
950         pud_t _pud;
951 
952         /*
953          * We should set the dirty bit only for FOLL_WRITE but for now
954          * the dirty bit in the pud is meaningless.  And if the dirty
955          * bit will become meaningful and we'll only set it with
956          * FOLL_WRITE, an atomic set_bit will be required on the pud to
957          * set the young bit, instead of the current set_pud_at.
958          */
959         _pud = pud_mkyoung(pud_mkdirty(*pud));
960         if (pudp_set_access_flags(vma, addr & HPAGE_PUD_MASK,
961                                 pud, _pud,  1))
962                 update_mmu_cache_pud(vma, addr, pud);
963 }
964 
965 struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
966                 pud_t *pud, int flags)
967 {
968         unsigned long pfn = pud_pfn(*pud);
969         struct mm_struct *mm = vma->vm_mm;
970         struct dev_pagemap *pgmap;
971         struct page *page;
972 
973         assert_spin_locked(pud_lockptr(mm, pud));
974 
975         if (flags & FOLL_WRITE && !pud_write(*pud))
976                 return NULL;
977 
978         if (pud_present(*pud) && pud_devmap(*pud))
979                 /* pass */;
980         else
981                 return NULL;
982 
983         if (flags & FOLL_TOUCH)
984                 touch_pud(vma, addr, pud);
985 
986         /*
987          * device mapped pages can only be returned if the
988          * caller will manage the page reference count.
989          */
990         if (!(flags & FOLL_GET))
991                 return ERR_PTR(-EEXIST);
992 
993         pfn += (addr & ~PUD_MASK) >> PAGE_SHIFT;
994         pgmap = get_dev_pagemap(pfn, NULL);
995         if (!pgmap)
996                 return ERR_PTR(-EFAULT);
997         page = pfn_to_page(pfn);
998         get_page(page);
999         put_dev_pagemap(pgmap);
1000 
1001         return page;
1002 }
1003 
1004 int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
1005                   pud_t *dst_pud, pud_t *src_pud, unsigned long addr,
1006                   struct vm_area_struct *vma)
1007 {
1008         spinlock_t *dst_ptl, *src_ptl;
1009         pud_t pud;
1010         int ret;
1011 
1012         dst_ptl = pud_lock(dst_mm, dst_pud);
1013         src_ptl = pud_lockptr(src_mm, src_pud);
1014         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
1015 
1016         ret = -EAGAIN;
1017         pud = *src_pud;
1018         if (unlikely(!pud_trans_huge(pud) && !pud_devmap(pud)))
1019                 goto out_unlock;
1020 
1021         /*
1022          * When page table lock is held, the huge zero pud should not be
1023          * under splitting since we don't split the page itself, only pud to
1024          * a page table.
1025          */
1026         if (is_huge_zero_pud(pud)) {
1027                 /* No huge zero pud yet */
1028         }
1029 
1030         pudp_set_wrprotect(src_mm, addr, src_pud);
1031         pud = pud_mkold(pud_wrprotect(pud));
1032         set_pud_at(dst_mm, addr, dst_pud, pud);
1033 
1034         ret = 0;
1035 out_unlock:
1036         spin_unlock(src_ptl);
1037         spin_unlock(dst_ptl);
1038         return ret;
1039 }
1040 
1041 void huge_pud_set_accessed(struct vm_fault *vmf, pud_t orig_pud)
1042 {
1043         pud_t entry;
1044         unsigned long haddr;
1045         bool write = vmf->flags & FAULT_FLAG_WRITE;
1046 
1047         vmf->ptl = pud_lock(vmf->vma->vm_mm, vmf->pud);
1048         if (unlikely(!pud_same(*vmf->pud, orig_pud)))
1049                 goto unlock;
1050 
1051         entry = pud_mkyoung(orig_pud);
1052         if (write)
1053                 entry = pud_mkdirty(entry);
1054         haddr = vmf->address & HPAGE_PUD_MASK;
1055         if (pudp_set_access_flags(vmf->vma, haddr, vmf->pud, entry, write))
1056                 update_mmu_cache_pud(vmf->vma, vmf->address, vmf->pud);
1057 
1058 unlock:
1059         spin_unlock(vmf->ptl);
1060 }
1061 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
1062 
1063 void huge_pmd_set_accessed(struct vm_fault *vmf, pmd_t orig_pmd)
1064 {
1065         pmd_t entry;
1066         unsigned long haddr;
1067         bool write = vmf->flags & FAULT_FLAG_WRITE;
1068 
1069         vmf->ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
1070         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
1071                 goto unlock;
1072 
1073         entry = pmd_mkyoung(orig_pmd);
1074         if (write)
1075                 entry = pmd_mkdirty(entry);
1076         haddr = vmf->address & HPAGE_PMD_MASK;
1077         if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry, write))
1078                 update_mmu_cache_pmd(vmf->vma, vmf->address, vmf->pmd);
1079 
1080 unlock:
1081         spin_unlock(vmf->ptl);
1082 }
1083 
1084 static int do_huge_pmd_wp_page_fallback(struct vm_fault *vmf, pmd_t orig_pmd,
1085                 struct page *page)
1086 {
1087         struct vm_area_struct *vma = vmf->vma;
1088         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
1089         struct mem_cgroup *memcg;
1090         pgtable_t pgtable;
1091         pmd_t _pmd;
1092         int ret = 0, i;
1093         struct page **pages;
1094         unsigned long mmun_start;       /* For mmu_notifiers */
1095         unsigned long mmun_end;         /* For mmu_notifiers */
1096 
1097         pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
1098                         GFP_KERNEL);
1099         if (unlikely(!pages)) {
1100                 ret |= VM_FAULT_OOM;
1101                 goto out;
1102         }
1103 
1104         for (i = 0; i < HPAGE_PMD_NR; i++) {
1105                 pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE, vma,
1106                                                vmf->address, page_to_nid(page));
1107                 if (unlikely(!pages[i] ||
1108                              mem_cgroup_try_charge(pages[i], vma->vm_mm,
1109                                      GFP_KERNEL, &memcg, false))) {
1110                         if (pages[i])
1111                                 put_page(pages[i]);
1112                         while (--i >= 0) {
1113                                 memcg = (void *)page_private(pages[i]);
1114                                 set_page_private(pages[i], 0);
1115                                 mem_cgroup_cancel_charge(pages[i], memcg,
1116                                                 false);
1117                                 put_page(pages[i]);
1118                         }
1119                         kfree(pages);
1120                         ret |= VM_FAULT_OOM;
1121                         goto out;
1122                 }
1123                 set_page_private(pages[i], (unsigned long)memcg);
1124         }
1125 
1126         for (i = 0; i < HPAGE_PMD_NR; i++) {
1127                 copy_user_highpage(pages[i], page + i,
1128                                    haddr + PAGE_SIZE * i, vma);
1129                 __SetPageUptodate(pages[i]);
1130                 cond_resched();
1131         }
1132 
1133         mmun_start = haddr;
1134         mmun_end   = haddr + HPAGE_PMD_SIZE;
1135         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
1136 
1137         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
1138         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
1139                 goto out_free_pages;
1140         VM_BUG_ON_PAGE(!PageHead(page), page);
1141 
1142         pmdp_huge_clear_flush_notify(vma, haddr, vmf->pmd);
1143         /* leave pmd empty until pte is filled */
1144 
1145         pgtable = pgtable_trans_huge_withdraw(vma->vm_mm, vmf->pmd);
1146         pmd_populate(vma->vm_mm, &_pmd, pgtable);
1147 
1148         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1149                 pte_t entry;
1150                 entry = mk_pte(pages[i], vma->vm_page_prot);
1151                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1152                 memcg = (void *)page_private(pages[i]);
1153                 set_page_private(pages[i], 0);
1154                 page_add_new_anon_rmap(pages[i], vmf->vma, haddr, false);
1155                 mem_cgroup_commit_charge(pages[i], memcg, false, false);
1156                 lru_cache_add_active_or_unevictable(pages[i], vma);
1157                 vmf->pte = pte_offset_map(&_pmd, haddr);
1158                 VM_BUG_ON(!pte_none(*vmf->pte));
1159                 set_pte_at(vma->vm_mm, haddr, vmf->pte, entry);
1160                 pte_unmap(vmf->pte);
1161         }
1162         kfree(pages);
1163 
1164         smp_wmb(); /* make pte visible before pmd */
1165         pmd_populate(vma->vm_mm, vmf->pmd, pgtable);
1166         page_remove_rmap(page, true);
1167         spin_unlock(vmf->ptl);
1168 
1169         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
1170 
1171         ret |= VM_FAULT_WRITE;
1172         put_page(page);
1173 
1174 out:
1175         return ret;
1176 
1177 out_free_pages:
1178         spin_unlock(vmf->ptl);
1179         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
1180         for (i = 0; i < HPAGE_PMD_NR; i++) {
1181                 memcg = (void *)page_private(pages[i]);
1182                 set_page_private(pages[i], 0);
1183                 mem_cgroup_cancel_charge(pages[i], memcg, false);
1184                 put_page(pages[i]);
1185         }
1186         kfree(pages);
1187         goto out;
1188 }
1189 
1190 int do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
1191 {
1192         struct vm_area_struct *vma = vmf->vma;
1193         struct page *page = NULL, *new_page;
1194         struct mem_cgroup *memcg;
1195         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
1196         unsigned long mmun_start;       /* For mmu_notifiers */
1197         unsigned long mmun_end;         /* For mmu_notifiers */
1198         gfp_t huge_gfp;                 /* for allocation and charge */
1199         int ret = 0;
1200 
1201         vmf->ptl = pmd_lockptr(vma->vm_mm, vmf->pmd);
1202         VM_BUG_ON_VMA(!vma->anon_vma, vma);
1203         if (is_huge_zero_pmd(orig_pmd))
1204                 goto alloc;
1205         spin_lock(vmf->ptl);
1206         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
1207                 goto out_unlock;
1208 
1209         page = pmd_page(orig_pmd);
1210         VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
1211         /*
1212          * We can only reuse the page if nobody else maps the huge page or it's
1213          * part.
1214          */
1215         if (page_trans_huge_mapcount(page, NULL) == 1) {
1216                 pmd_t entry;
1217                 entry = pmd_mkyoung(orig_pmd);
1218                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1219                 if (pmdp_set_access_flags(vma, haddr, vmf->pmd, entry,  1))
1220                         update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
1221                 ret |= VM_FAULT_WRITE;
1222                 goto out_unlock;
1223         }
1224         get_page(page);
1225         spin_unlock(vmf->ptl);
1226 alloc:
1227         if (transparent_hugepage_enabled(vma) &&
1228             !transparent_hugepage_debug_cow()) {
1229                 huge_gfp = alloc_hugepage_direct_gfpmask(vma);
1230                 new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
1231         } else
1232                 new_page = NULL;
1233 
1234         if (likely(new_page)) {
1235                 prep_transhuge_page(new_page);
1236         } else {
1237                 if (!page) {
1238                         split_huge_pmd(vma, vmf->pmd, vmf->address);
1239                         ret |= VM_FAULT_FALLBACK;
1240                 } else {
1241                         ret = do_huge_pmd_wp_page_fallback(vmf, orig_pmd, page);
1242                         if (ret & VM_FAULT_OOM) {
1243                                 split_huge_pmd(vma, vmf->pmd, vmf->address);
1244                                 ret |= VM_FAULT_FALLBACK;
1245                         }
1246                         put_page(page);
1247                 }
1248                 count_vm_event(THP_FAULT_FALLBACK);
1249                 goto out;
1250         }
1251 
1252         if (unlikely(mem_cgroup_try_charge(new_page, vma->vm_mm,
1253                                         huge_gfp, &memcg, true))) {
1254                 put_page(new_page);
1255                 split_huge_pmd(vma, vmf->pmd, vmf->address);
1256                 if (page)
1257                         put_page(page);
1258                 ret |= VM_FAULT_FALLBACK;
1259                 count_vm_event(THP_FAULT_FALLBACK);
1260                 goto out;
1261         }
1262 
1263         count_vm_event(THP_FAULT_ALLOC);
1264 
1265         if (!page)
1266                 clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1267         else
1268                 copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1269         __SetPageUptodate(new_page);
1270 
1271         mmun_start = haddr;
1272         mmun_end   = haddr + HPAGE_PMD_SIZE;
1273         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
1274 
1275         spin_lock(vmf->ptl);
1276         if (page)
1277                 put_page(page);
1278         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd))) {
1279                 spin_unlock(vmf->ptl);
1280                 mem_cgroup_cancel_charge(new_page, memcg, true);
1281                 put_page(new_page);
1282                 goto out_mn;
1283         } else {
1284                 pmd_t entry;
1285                 entry = mk_huge_pmd(new_page, vma->vm_page_prot);
1286                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1287                 pmdp_huge_clear_flush_notify(vma, haddr, vmf->pmd);
1288                 page_add_new_anon_rmap(new_page, vma, haddr, true);
1289                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1290                 lru_cache_add_active_or_unevictable(new_page, vma);
1291                 set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
1292                 update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
1293                 if (!page) {
1294                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
1295                 } else {
1296                         VM_BUG_ON_PAGE(!PageHead(page), page);
1297                         page_remove_rmap(page, true);
1298                         put_page(page);
1299                 }
1300                 ret |= VM_FAULT_WRITE;
1301         }
1302         spin_unlock(vmf->ptl);
1303 out_mn:
1304         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
1305 out:
1306         return ret;
1307 out_unlock:
1308         spin_unlock(vmf->ptl);
1309         return ret;
1310 }
1311 
1312 /*
1313  * FOLL_FORCE can write to even unwritable pmd's, but only
1314  * after we've gone through a COW cycle and they are dirty.
1315  */
1316 static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags)
1317 {
1318         return pmd_write(pmd) ||
1319                ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd));
1320 }
1321 
1322 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1323                                    unsigned long addr,
1324                                    pmd_t *pmd,
1325                                    unsigned int flags)
1326 {
1327         struct mm_struct *mm = vma->vm_mm;
1328         struct page *page = NULL;
1329 
1330         assert_spin_locked(pmd_lockptr(mm, pmd));
1331 
1332         if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags))
1333                 goto out;
1334 
1335         /* Avoid dumping huge zero page */
1336         if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1337                 return ERR_PTR(-EFAULT);
1338 
1339         /* Full NUMA hinting faults to serialise migration in fault paths */
1340         if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
1341                 goto out;
1342 
1343         page = pmd_page(*pmd);
1344         VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
1345         if (flags & FOLL_TOUCH)
1346                 touch_pmd(vma, addr, pmd);
1347         if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
1348                 /*
1349                  * We don't mlock() pte-mapped THPs. This way we can avoid
1350                  * leaking mlocked pages into non-VM_LOCKED VMAs.
1351                  *
1352                  * For anon THP:
1353                  *
1354                  * In most cases the pmd is the only mapping of the page as we
1355                  * break COW for the mlock() -- see gup_flags |= FOLL_WRITE for
1356                  * writable private mappings in populate_vma_page_range().
1357                  *
1358                  * The only scenario when we have the page shared here is if we
1359                  * mlocking read-only mapping shared over fork(). We skip
1360                  * mlocking such pages.
1361                  *
1362                  * For file THP:
1363                  *
1364                  * We can expect PageDoubleMap() to be stable under page lock:
1365                  * for file pages we set it in page_add_file_rmap(), which
1366                  * requires page to be locked.
1367                  */
1368 
1369                 if (PageAnon(page) && compound_mapcount(page) != 1)
1370                         goto skip_mlock;
1371                 if (PageDoubleMap(page) || !page->mapping)
1372                         goto skip_mlock;
1373                 if (!trylock_page(page))
1374                         goto skip_mlock;
1375                 lru_add_drain();
1376                 if (page->mapping && !PageDoubleMap(page))
1377                         mlock_vma_page(page);
1378                 unlock_page(page);
1379         }
1380 skip_mlock:
1381         page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1382         VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
1383         if (flags & FOLL_GET)
1384                 get_page(page);
1385 
1386 out:
1387         return page;
1388 }
1389 
1390 /* NUMA hinting page fault entry point for trans huge pmds */
1391 int do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t pmd)
1392 {
1393         struct vm_area_struct *vma = vmf->vma;
1394         struct anon_vma *anon_vma = NULL;
1395         struct page *page;
1396         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
1397         int page_nid = -1, this_nid = numa_node_id();
1398         int target_nid, last_cpupid = -1;
1399         bool page_locked;
1400         bool migrated = false;
1401         bool was_writable;
1402         int flags = 0;
1403 
1404         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
1405         if (unlikely(!pmd_same(pmd, *vmf->pmd)))
1406                 goto out_unlock;
1407 
1408         /*
1409          * If there are potential migrations, wait for completion and retry
1410          * without disrupting NUMA hinting information. Do not relock and
1411          * check_same as the page may no longer be mapped.
1412          */
1413         if (unlikely(pmd_trans_migrating(*vmf->pmd))) {
1414                 page = pmd_page(*vmf->pmd);
1415                 if (!get_page_unless_zero(page))
1416                         goto out_unlock;
1417                 spin_unlock(vmf->ptl);
1418                 wait_on_page_locked(page);
1419                 put_page(page);
1420                 goto out;
1421         }
1422 
1423         page = pmd_page(pmd);
1424         BUG_ON(is_huge_zero_page(page));
1425         page_nid = page_to_nid(page);
1426         last_cpupid = page_cpupid_last(page);
1427         count_vm_numa_event(NUMA_HINT_FAULTS);
1428         if (page_nid == this_nid) {
1429                 count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1430                 flags |= TNF_FAULT_LOCAL;
1431         }
1432 
1433         /* See similar comment in do_numa_page for explanation */
1434         if (!pmd_savedwrite(pmd))
1435                 flags |= TNF_NO_GROUP;
1436 
1437         /*
1438          * Acquire the page lock to serialise THP migrations but avoid dropping
1439          * page_table_lock if at all possible
1440          */
1441         page_locked = trylock_page(page);
1442         target_nid = mpol_misplaced(page, vma, haddr);
1443         if (target_nid == -1) {
1444                 /* If the page was locked, there are no parallel migrations */
1445                 if (page_locked)
1446                         goto clear_pmdnuma;
1447         }
1448 
1449         /* Migration could have started since the pmd_trans_migrating check */
1450         if (!page_locked) {
1451                 page_nid = -1;
1452                 if (!get_page_unless_zero(page))
1453                         goto out_unlock;
1454                 spin_unlock(vmf->ptl);
1455                 wait_on_page_locked(page);
1456                 put_page(page);
1457                 goto out;
1458         }
1459 
1460         /*
1461          * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
1462          * to serialises splits
1463          */
1464         get_page(page);
1465         spin_unlock(vmf->ptl);
1466         anon_vma = page_lock_anon_vma_read(page);
1467 
1468         /* Confirm the PMD did not change while page_table_lock was released */
1469         spin_lock(vmf->ptl);
1470         if (unlikely(!pmd_same(pmd, *vmf->pmd))) {
1471                 unlock_page(page);
1472                 put_page(page);
1473                 page_nid = -1;
1474                 goto out_unlock;
1475         }
1476 
1477         /* Bail if we fail to protect against THP splits for any reason */
1478         if (unlikely(!anon_vma)) {
1479                 put_page(page);
1480                 page_nid = -1;
1481                 goto clear_pmdnuma;
1482         }
1483 
1484         /*
1485          * Migrate the THP to the requested node, returns with page unlocked
1486          * and access rights restored.
1487          */
1488         spin_unlock(vmf->ptl);
1489         migrated = migrate_misplaced_transhuge_page(vma->vm_mm, vma,
1490                                 vmf->pmd, pmd, vmf->address, page, target_nid);
1491         if (migrated) {
1492                 flags |= TNF_MIGRATED;
1493                 page_nid = target_nid;
1494         } else
1495                 flags |= TNF_MIGRATE_FAIL;
1496 
1497         goto out;
1498 clear_pmdnuma:
1499         BUG_ON(!PageLocked(page));
1500         was_writable = pmd_savedwrite(pmd);
1501         pmd = pmd_modify(pmd, vma->vm_page_prot);
1502         pmd = pmd_mkyoung(pmd);
1503         if (was_writable)
1504                 pmd = pmd_mkwrite(pmd);
1505         set_pmd_at(vma->vm_mm, haddr, vmf->pmd, pmd);
1506         update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
1507         unlock_page(page);
1508 out_unlock:
1509         spin_unlock(vmf->ptl);
1510 
1511 out:
1512         if (anon_vma)
1513                 page_unlock_anon_vma_read(anon_vma);
1514 
1515         if (page_nid != -1)
1516                 task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR,
1517                                 flags);
1518 
1519         return 0;
1520 }
1521 
1522 /*
1523  * Return true if we do MADV_FREE successfully on entire pmd page.
1524  * Otherwise, return false.
1525  */
1526 bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1527                 pmd_t *pmd, unsigned long addr, unsigned long next)
1528 {
1529         spinlock_t *ptl;
1530         pmd_t orig_pmd;
1531         struct page *page;
1532         struct mm_struct *mm = tlb->mm;
1533         bool ret = false;
1534 
1535         tlb_remove_check_page_size_change(tlb, HPAGE_PMD_SIZE);
1536 
1537         ptl = pmd_trans_huge_lock(pmd, vma);
1538         if (!ptl)
1539                 goto out_unlocked;
1540 
1541         orig_pmd = *pmd;
1542         if (is_huge_zero_pmd(orig_pmd))
1543                 goto out;
1544 
1545         page = pmd_page(orig_pmd);
1546         /*
1547          * If other processes are mapping this page, we couldn't discard
1548          * the page unless they all do MADV_FREE so let's skip the page.
1549          */
1550         if (page_mapcount(page) != 1)
1551                 goto out;
1552 
1553         if (!trylock_page(page))
1554                 goto out;
1555 
1556         /*
1557          * If user want to discard part-pages of THP, split it so MADV_FREE
1558          * will deactivate only them.
1559          */
1560         if (next - addr != HPAGE_PMD_SIZE) {
1561                 get_page(page);
1562                 spin_unlock(ptl);
1563                 split_huge_page(page);
1564                 unlock_page(page);
1565                 put_page(page);
1566                 goto out_unlocked;
1567         }
1568 
1569         if (PageDirty(page))
1570                 ClearPageDirty(page);
1571         unlock_page(page);
1572 
1573         if (PageActive(page))
1574                 deactivate_page(page);
1575 
1576         if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
1577                 pmdp_invalidate(vma, addr, pmd);
1578                 orig_pmd = pmd_mkold(orig_pmd);
1579                 orig_pmd = pmd_mkclean(orig_pmd);
1580 
1581                 set_pmd_at(mm, addr, pmd, orig_pmd);
1582                 tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1583         }
1584         ret = true;
1585 out:
1586         spin_unlock(ptl);
1587 out_unlocked:
1588         return ret;
1589 }
1590 
1591 static inline void zap_deposited_table(struct mm_struct *mm, pmd_t *pmd)
1592 {
1593         pgtable_t pgtable;
1594 
1595         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1596         pte_free(mm, pgtable);
1597         atomic_long_dec(&mm->nr_ptes);
1598 }
1599 
1600 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1601                  pmd_t *pmd, unsigned long addr)
1602 {
1603         pmd_t orig_pmd;
1604         spinlock_t *ptl;
1605 
1606         tlb_remove_check_page_size_change(tlb, HPAGE_PMD_SIZE);
1607 
1608         ptl = __pmd_trans_huge_lock(pmd, vma);
1609         if (!ptl)
1610                 return 0;
1611         /*
1612          * For architectures like ppc64 we look at deposited pgtable
1613          * when calling pmdp_huge_get_and_clear. So do the
1614          * pgtable_trans_huge_withdraw after finishing pmdp related
1615          * operations.
1616          */
1617         orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
1618                         tlb->fullmm);
1619         tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1620         if (vma_is_dax(vma)) {
1621                 spin_unlock(ptl);
1622                 if (is_huge_zero_pmd(orig_pmd))
1623                         tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
1624         } else if (is_huge_zero_pmd(orig_pmd)) {
1625                 pte_free(tlb->mm, pgtable_trans_huge_withdraw(tlb->mm, pmd));
1626                 atomic_long_dec(&tlb->mm->nr_ptes);
1627                 spin_unlock(ptl);
1628                 tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
1629         } else {
1630                 struct page *page = pmd_page(orig_pmd);
1631                 page_remove_rmap(page, true);
1632                 VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
1633                 VM_BUG_ON_PAGE(!PageHead(page), page);
1634                 if (PageAnon(page)) {
1635                         pgtable_t pgtable;
1636                         pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
1637                         pte_free(tlb->mm, pgtable);
1638                         atomic_long_dec(&tlb->mm->nr_ptes);
1639                         add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1640                 } else {
1641                         if (arch_needs_pgtable_deposit())
1642                                 zap_deposited_table(tlb->mm, pmd);
1643                         add_mm_counter(tlb->mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1644                 }
1645                 spin_unlock(ptl);
1646                 tlb_remove_page_size(tlb, page, HPAGE_PMD_SIZE);
1647         }
1648         return 1;
1649 }
1650 
1651 #ifndef pmd_move_must_withdraw
1652 static inline int pmd_move_must_withdraw(spinlock_t *new_pmd_ptl,
1653                                          spinlock_t *old_pmd_ptl,
1654                                          struct vm_area_struct *vma)
1655 {
1656         /*
1657          * With split pmd lock we also need to move preallocated
1658          * PTE page table if new_pmd is on different PMD page table.
1659          *
1660          * We also don't deposit and withdraw tables for file pages.
1661          */
1662         return (new_pmd_ptl != old_pmd_ptl) && vma_is_anonymous(vma);
1663 }
1664 #endif
1665 
1666 bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
1667                   unsigned long new_addr, unsigned long old_end,
1668                   pmd_t *old_pmd, pmd_t *new_pmd, bool *need_flush)
1669 {
1670         spinlock_t *old_ptl, *new_ptl;
1671         pmd_t pmd;
1672         struct mm_struct *mm = vma->vm_mm;
1673         bool force_flush = false;
1674 
1675         if ((old_addr & ~HPAGE_PMD_MASK) ||
1676             (new_addr & ~HPAGE_PMD_MASK) ||
1677             old_end - old_addr < HPAGE_PMD_SIZE)
1678                 return false;
1679 
1680         /*
1681          * The destination pmd shouldn't be established, free_pgtables()
1682          * should have release it.
1683          */
1684         if (WARN_ON(!pmd_none(*new_pmd))) {
1685                 VM_BUG_ON(pmd_trans_huge(*new_pmd));
1686                 return false;
1687         }
1688 
1689         /*
1690          * We don't have to worry about the ordering of src and dst
1691          * ptlocks because exclusive mmap_sem prevents deadlock.
1692          */
1693         old_ptl = __pmd_trans_huge_lock(old_pmd, vma);
1694         if (old_ptl) {
1695                 new_ptl = pmd_lockptr(mm, new_pmd);
1696                 if (new_ptl != old_ptl)
1697                         spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
1698                 pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
1699                 if (pmd_present(pmd) && pmd_dirty(pmd))
1700                         force_flush = true;
1701                 VM_BUG_ON(!pmd_none(*new_pmd));
1702 
1703                 if (pmd_move_must_withdraw(new_ptl, old_ptl, vma)) {
1704                         pgtable_t pgtable;
1705                         pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
1706                         pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
1707                 }
1708                 set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
1709                 if (new_ptl != old_ptl)
1710                         spin_unlock(new_ptl);
1711                 if (force_flush)
1712                         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
1713                 else
1714                         *need_flush = true;
1715                 spin_unlock(old_ptl);
1716                 return true;
1717         }
1718         return false;
1719 }
1720 
1721 /*
1722  * Returns
1723  *  - 0 if PMD could not be locked
1724  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1725  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1726  */
1727 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1728                 unsigned long addr, pgprot_t newprot, int prot_numa)
1729 {
1730         struct mm_struct *mm = vma->vm_mm;
1731         spinlock_t *ptl;
1732         pmd_t entry;
1733         bool preserve_write;
1734         int ret;
1735 
1736         ptl = __pmd_trans_huge_lock(pmd, vma);
1737         if (!ptl)
1738                 return 0;
1739 
1740         preserve_write = prot_numa && pmd_write(*pmd);
1741         ret = 1;
1742 
1743         /*
1744          * Avoid trapping faults against the zero page. The read-only
1745          * data is likely to be read-cached on the local CPU and
1746          * local/remote hits to the zero page are not interesting.
1747          */
1748         if (prot_numa && is_huge_zero_pmd(*pmd))
1749                 goto unlock;
1750 
1751         if (prot_numa && pmd_protnone(*pmd))
1752                 goto unlock;
1753 
1754         /*
1755          * In case prot_numa, we are under down_read(mmap_sem). It's critical
1756          * to not clear pmd intermittently to avoid race with MADV_DONTNEED
1757          * which is also under down_read(mmap_sem):
1758          *
1759          *      CPU0:                           CPU1:
1760          *                              change_huge_pmd(prot_numa=1)
1761          *                               pmdp_huge_get_and_clear_notify()
1762          * madvise_dontneed()
1763          *  zap_pmd_range()
1764          *   pmd_trans_huge(*pmd) == 0 (without ptl)
1765          *   // skip the pmd
1766          *                               set_pmd_at();
1767          *                               // pmd is re-established
1768          *
1769          * The race makes MADV_DONTNEED miss the huge pmd and don't clear it
1770          * which may break userspace.
1771          *
1772          * pmdp_invalidate() is required to make sure we don't miss
1773          * dirty/young flags set by hardware.
1774          */
1775         entry = *pmd;
1776         pmdp_invalidate(vma, addr, pmd);
1777 
1778         /*
1779          * Recover dirty/young flags.  It relies on pmdp_invalidate to not
1780          * corrupt them.
1781          */
1782         if (pmd_dirty(*pmd))
1783                 entry = pmd_mkdirty(entry);
1784         if (pmd_young(*pmd))
1785                 entry = pmd_mkyoung(entry);
1786 
1787         entry = pmd_modify(entry, newprot);
1788         if (preserve_write)
1789                 entry = pmd_mk_savedwrite(entry);
1790         ret = HPAGE_PMD_NR;
1791         set_pmd_at(mm, addr, pmd, entry);
1792         BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));
1793 unlock:
1794         spin_unlock(ptl);
1795         return ret;
1796 }
1797 
1798 /*
1799  * Returns page table lock pointer if a given pmd maps a thp, NULL otherwise.
1800  *
1801  * Note that if it returns page table lock pointer, this routine returns without
1802  * unlocking page table lock. So callers must unlock it.
1803  */
1804 spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
1805 {
1806         spinlock_t *ptl;
1807         ptl = pmd_lock(vma->vm_mm, pmd);
1808         if (likely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
1809                 return ptl;
1810         spin_unlock(ptl);
1811         return NULL;
1812 }
1813 
1814 /*
1815  * Returns true if a given pud maps a thp, false otherwise.
1816  *
1817  * Note that if it returns true, this routine returns without unlocking page
1818  * table lock. So callers must unlock it.
1819  */
1820 spinlock_t *__pud_trans_huge_lock(pud_t *pud, struct vm_area_struct *vma)
1821 {
1822         spinlock_t *ptl;
1823 
1824         ptl = pud_lock(vma->vm_mm, pud);
1825         if (likely(pud_trans_huge(*pud) || pud_devmap(*pud)))
1826                 return ptl;
1827         spin_unlock(ptl);
1828         return NULL;
1829 }
1830 
1831 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
1832 int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
1833                  pud_t *pud, unsigned long addr)
1834 {
1835         pud_t orig_pud;
1836         spinlock_t *ptl;
1837 
1838         ptl = __pud_trans_huge_lock(pud, vma);
1839         if (!ptl)
1840                 return 0;
1841         /*
1842          * For architectures like ppc64 we look at deposited pgtable
1843          * when calling pudp_huge_get_and_clear. So do the
1844          * pgtable_trans_huge_withdraw after finishing pudp related
1845          * operations.
1846          */
1847         orig_pud = pudp_huge_get_and_clear_full(tlb->mm, addr, pud,
1848                         tlb->fullmm);
1849         tlb_remove_pud_tlb_entry(tlb, pud, addr);
1850         if (vma_is_dax(vma)) {
1851                 spin_unlock(ptl);
1852                 /* No zero page support yet */
1853         } else {
1854                 /* No support for anonymous PUD pages yet */
1855                 BUG();
1856         }
1857         return 1;
1858 }
1859 
1860 static void __split_huge_pud_locked(struct vm_area_struct *vma, pud_t *pud,
1861                 unsigned long haddr)
1862 {
1863         VM_BUG_ON(haddr & ~HPAGE_PUD_MASK);
1864         VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
1865         VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PUD_SIZE, vma);
1866         VM_BUG_ON(!pud_trans_huge(*pud) && !pud_devmap(*pud));
1867 
1868         count_vm_event(THP_SPLIT_PUD);
1869 
1870         pudp_huge_clear_flush_notify(vma, haddr, pud);
1871 }
1872 
1873 void __split_huge_pud(struct vm_area_struct *vma, pud_t *pud,
1874                 unsigned long address)
1875 {
1876         spinlock_t *ptl;
1877         struct mm_struct *mm = vma->vm_mm;
1878         unsigned long haddr = address & HPAGE_PUD_MASK;
1879 
1880         mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PUD_SIZE);
1881         ptl = pud_lock(mm, pud);
1882         if (unlikely(!pud_trans_huge(*pud) && !pud_devmap(*pud)))
1883                 goto out;
1884         __split_huge_pud_locked(vma, pud, haddr);
1885 
1886 out:
1887         spin_unlock(ptl);
1888         mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PUD_SIZE);
1889 }
1890 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
1891 
1892 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
1893                 unsigned long haddr, pmd_t *pmd)
1894 {
1895         struct mm_struct *mm = vma->vm_mm;
1896         pgtable_t pgtable;
1897         pmd_t _pmd;
1898         int i;
1899 
1900         /* leave pmd empty until pte is filled */
1901         pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1902 
1903         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1904         pmd_populate(mm, &_pmd, pgtable);
1905 
1906         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1907                 pte_t *pte, entry;
1908                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
1909                 entry = pte_mkspecial(entry);
1910                 pte = pte_offset_map(&_pmd, haddr);
1911                 VM_BUG_ON(!pte_none(*pte));
1912                 set_pte_at(mm, haddr, pte, entry);
1913                 pte_unmap(pte);
1914         }
1915         smp_wmb(); /* make pte visible before pmd */
1916         pmd_populate(mm, pmd, pgtable);
1917 }
1918 
1919 static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
1920                 unsigned long haddr, bool freeze)
1921 {
1922         struct mm_struct *mm = vma->vm_mm;
1923         struct page *page;
1924         pgtable_t pgtable;
1925         pmd_t _pmd;
1926         bool young, write, dirty, soft_dirty;
1927         unsigned long addr;
1928         int i;
1929 
1930         VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
1931         VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
1932         VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
1933         VM_BUG_ON(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd));
1934 
1935         count_vm_event(THP_SPLIT_PMD);
1936 
1937         if (!vma_is_anonymous(vma)) {
1938                 _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1939                 /*
1940                  * We are going to unmap this huge page. So
1941                  * just go ahead and zap it
1942                  */
1943                 if (arch_needs_pgtable_deposit())
1944                         zap_deposited_table(mm, pmd);
1945                 if (vma_is_dax(vma))
1946                         return;
1947                 page = pmd_page(_pmd);
1948                 if (!PageReferenced(page) && pmd_young(_pmd))
1949                         SetPageReferenced(page);
1950                 page_remove_rmap(page, true);
1951                 put_page(page);
1952                 add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1953                 return;
1954         } else if (is_huge_zero_pmd(*pmd)) {
1955                 return __split_huge_zero_page_pmd(vma, haddr, pmd);
1956         }
1957 
1958         page = pmd_page(*pmd);
1959         VM_BUG_ON_PAGE(!page_count(page), page);
1960         page_ref_add(page, HPAGE_PMD_NR - 1);
1961         write = pmd_write(*pmd);
1962         young = pmd_young(*pmd);
1963         dirty = pmd_dirty(*pmd);
1964         soft_dirty = pmd_soft_dirty(*pmd);
1965 
1966         pmdp_huge_split_prepare(vma, haddr, pmd);
1967         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1968         pmd_populate(mm, &_pmd, pgtable);
1969 
1970         for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
1971                 pte_t entry, *pte;
1972                 /*
1973                  * Note that NUMA hinting access restrictions are not
1974                  * transferred to avoid any possibility of altering
1975                  * permissions across VMAs.
1976                  */
1977                 if (freeze) {
1978                         swp_entry_t swp_entry;
1979                         swp_entry = make_migration_entry(page + i, write);
1980                         entry = swp_entry_to_pte(swp_entry);
1981                         if (soft_dirty)
1982                                 entry = pte_swp_mksoft_dirty(entry);
1983                 } else {
1984                         entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
1985                         entry = maybe_mkwrite(entry, vma);
1986                         if (!write)
1987                                 entry = pte_wrprotect(entry);
1988                         if (!young)
1989                                 entry = pte_mkold(entry);
1990                         if (soft_dirty)
1991                                 entry = pte_mksoft_dirty(entry);
1992                 }
1993                 if (dirty)
1994                         SetPageDirty(page + i);
1995                 pte = pte_offset_map(&_pmd, addr);
1996                 BUG_ON(!pte_none(*pte));
1997                 set_pte_at(mm, addr, pte, entry);
1998                 atomic_inc(&page[i]._mapcount);
1999                 pte_unmap(pte);
2000         }
2001 
2002         /*
2003          * Set PG_double_map before dropping compound_mapcount to avoid
2004          * false-negative page_mapped().
2005          */
2006         if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
2007                 for (i = 0; i < HPAGE_PMD_NR; i++)
2008                         atomic_inc(&page[i]._mapcount);
2009         }
2010 
2011         if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
2012                 /* Last compound_mapcount is gone. */
2013                 __dec_node_page_state(page, NR_ANON_THPS);
2014                 if (TestClearPageDoubleMap(page)) {
2015                         /* No need in mapcount reference anymore */
2016                         for (i = 0; i < HPAGE_PMD_NR; i++)
2017                                 atomic_dec(&page[i]._mapcount);
2018                 }
2019         }
2020 
2021         smp_wmb(); /* make pte visible before pmd */
2022         /*
2023          * Up to this point the pmd is present and huge and userland has the
2024          * whole access to the hugepage during the split (which happens in
2025          * place). If we overwrite the pmd with the not-huge version pointing
2026          * to the pte here (which of course we could if all CPUs were bug
2027          * free), userland could trigger a small page size TLB miss on the
2028          * small sized TLB while the hugepage TLB entry is still established in
2029          * the huge TLB. Some CPU doesn't like that.
2030          * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum
2031          * 383 on page 93. Intel should be safe but is also warns that it's
2032          * only safe if the permission and cache attributes of the two entries
2033          * loaded in the two TLB is identical (which should be the case here).
2034          * But it is generally safer to never allow small and huge TLB entries
2035          * for the same virtual address to be loaded simultaneously. So instead
2036          * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the
2037          * current pmd notpresent (atomically because here the pmd_trans_huge
2038          * and pmd_trans_splitting must remain set at all times on the pmd
2039          * until the split is complete for this pmd), then we flush the SMP TLB
2040          * and finally we write the non-huge version of the pmd entry with
2041          * pmd_populate.
2042          */
2043         pmdp_invalidate(vma, haddr, pmd);
2044         pmd_populate(mm, pmd, pgtable);
2045 
2046         if (freeze) {
2047                 for (i = 0; i < HPAGE_PMD_NR; i++) {
2048                         page_remove_rmap(page + i, false);
2049                         put_page(page + i);
2050                 }
2051         }
2052 }
2053 
2054 void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
2055                 unsigned long address, bool freeze, struct page *page)
2056 {
2057         spinlock_t *ptl;
2058         struct mm_struct *mm = vma->vm_mm;
2059         unsigned long haddr = address & HPAGE_PMD_MASK;
2060 
2061         mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
2062         ptl = pmd_lock(mm, pmd);
2063 
2064         /*
2065          * If caller asks to setup a migration entries, we need a page to check
2066          * pmd against. Otherwise we can end up replacing wrong page.
2067          */
2068         VM_BUG_ON(freeze && !page);
2069         if (page && page != pmd_page(*pmd))
2070                 goto out;
2071 
2072         if (pmd_trans_huge(*pmd)) {
2073                 page = pmd_page(*pmd);
2074                 if (PageMlocked(page))
2075                         clear_page_mlock(page);
2076         } else if (!pmd_devmap(*pmd))
2077                 goto out;
2078         __split_huge_pmd_locked(vma, pmd, haddr, freeze);
2079 out:
2080         spin_unlock(ptl);
2081         mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
2082 }
2083 
2084 void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
2085                 bool freeze, struct page *page)
2086 {
2087         pgd_t *pgd;
2088         p4d_t *p4d;
2089         pud_t *pud;
2090         pmd_t *pmd;
2091 
2092         pgd = pgd_offset(vma->vm_mm, address);
2093         if (!pgd_present(*pgd))
2094                 return;
2095 
2096         p4d = p4d_offset(pgd, address);
2097         if (!p4d_present(*p4d))
2098                 return;
2099 
2100         pud = pud_offset(p4d, address);
2101         if (!pud_present(*pud))
2102                 return;
2103 
2104         pmd = pmd_offset(pud, address);
2105 
2106         __split_huge_pmd(vma, pmd, address, freeze, page);
2107 }
2108 
2109 void vma_adjust_trans_huge(struct vm_area_struct *vma,
2110                              unsigned long start,
2111                              unsigned long end,
2112                              long adjust_next)
2113 {
2114         /*
2115          * If the new start address isn't hpage aligned and it could
2116          * previously contain an hugepage: check if we need to split
2117          * an huge pmd.
2118          */
2119         if (start & ~HPAGE_PMD_MASK &&
2120             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
2121             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2122                 split_huge_pmd_address(vma, start, false, NULL);
2123 
2124         /*
2125          * If the new end address isn't hpage aligned and it could
2126          * previously contain an hugepage: check if we need to split
2127          * an huge pmd.
2128          */
2129         if (end & ~HPAGE_PMD_MASK &&
2130             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
2131             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2132                 split_huge_pmd_address(vma, end, false, NULL);
2133 
2134         /*
2135          * If we're also updating the vma->vm_next->vm_start, if the new
2136          * vm_next->vm_start isn't page aligned and it could previously
2137          * contain an hugepage: check if we need to split an huge pmd.
2138          */
2139         if (adjust_next > 0) {
2140                 struct vm_area_struct *next = vma->vm_next;
2141                 unsigned long nstart = next->vm_start;
2142                 nstart += adjust_next << PAGE_SHIFT;
2143                 if (nstart & ~HPAGE_PMD_MASK &&
2144                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
2145                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
2146                         split_huge_pmd_address(next, nstart, false, NULL);
2147         }
2148 }
2149 
2150 static void freeze_page(struct page *page)
2151 {
2152         enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
2153                 TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD;
2154         int ret;
2155 
2156         VM_BUG_ON_PAGE(!PageHead(page), page);
2157 
2158         if (PageAnon(page))
2159                 ttu_flags |= TTU_MIGRATION;
2160 
2161         ret = try_to_unmap(page, ttu_flags);
2162         VM_BUG_ON_PAGE(ret, page);
2163 }
2164 
2165 static void unfreeze_page(struct page *page)
2166 {
2167         int i;
2168         if (PageTransHuge(page)) {
2169                 remove_migration_ptes(page, page, true);
2170         } else {
2171                 for (i = 0; i < HPAGE_PMD_NR; i++)
2172                         remove_migration_ptes(page + i, page + i, true);
2173         }
2174 }
2175 
2176 static void __split_huge_page_tail(struct page *head, int tail,
2177                 struct lruvec *lruvec, struct list_head *list)
2178 {
2179         struct page *page_tail = head + tail;
2180 
2181         VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
2182         VM_BUG_ON_PAGE(page_ref_count(page_tail) != 0, page_tail);
2183 
2184         /*
2185          * tail_page->_refcount is zero and not changing from under us. But
2186          * get_page_unless_zero() may be running from under us on the
2187          * tail_page. If we used atomic_set() below instead of atomic_inc() or
2188          * atomic_add(), we would then run atomic_set() concurrently with
2189          * get_page_unless_zero(), and atomic_set() is implemented in C not
2190          * using locked ops. spin_unlock on x86 sometime uses locked ops
2191          * because of PPro errata 66, 92, so unless somebody can guarantee
2192          * atomic_set() here would be safe on all archs (and not only on x86),
2193          * it's safer to use atomic_inc()/atomic_add().
2194          */
2195         if (PageAnon(head)) {
2196                 page_ref_inc(page_tail);
2197         } else {
2198                 /* Additional pin to radix tree */
2199                 page_ref_add(page_tail, 2);
2200         }
2201 
2202         page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
2203         page_tail->flags |= (head->flags &
2204                         ((1L << PG_referenced) |
2205                          (1L << PG_swapbacked) |
2206                          (1L << PG_mlocked) |
2207                          (1L << PG_uptodate) |
2208                          (1L << PG_active) |
2209                          (1L << PG_locked) |
2210                          (1L << PG_unevictable) |
2211                          (1L << PG_dirty)));
2212 
2213         /*
2214          * After clearing PageTail the gup refcount can be released.
2215          * Page flags also must be visible before we make the page non-compound.
2216          */
2217         smp_wmb();
2218 
2219         clear_compound_head(page_tail);
2220 
2221         if (page_is_young(head))
2222                 set_page_young(page_tail);
2223         if (page_is_idle(head))
2224                 set_page_idle(page_tail);
2225 
2226         /* ->mapping in first tail page is compound_mapcount */
2227         VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
2228                         page_tail);
2229         page_tail->mapping = head->mapping;
2230 
2231         page_tail->index = head->index + tail;
2232         page_cpupid_xchg_last(page_tail, page_cpupid_last(head));
2233         lru_add_page_tail(head, page_tail, lruvec, list);
2234 }
2235 
2236 static void __split_huge_page(struct page *page, struct list_head *list,
2237                 unsigned long flags)
2238 {
2239         struct page *head = compound_head(page);
2240         struct zone *zone = page_zone(head);
2241         struct lruvec *lruvec;
2242         pgoff_t end = -1;
2243         int i;
2244 
2245         lruvec = mem_cgroup_page_lruvec(head, zone->zone_pgdat);
2246 
2247         /* complete memcg works before add pages to LRU */
2248         mem_cgroup_split_huge_fixup(head);
2249 
2250         if (!PageAnon(page))
2251                 end = DIV_ROUND_UP(i_size_read(head->mapping->host), PAGE_SIZE);
2252 
2253         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
2254                 __split_huge_page_tail(head, i, lruvec, list);
2255                 /* Some pages can be beyond i_size: drop them from page cache */
2256                 if (head[i].index >= end) {
2257                         __ClearPageDirty(head + i);
2258                         __delete_from_page_cache(head + i, NULL);
2259                         if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
2260                                 shmem_uncharge(head->mapping->host, 1);
2261                         put_page(head + i);
2262                 }
2263         }
2264 
2265         ClearPageCompound(head);
2266         /* See comment in __split_huge_page_tail() */
2267         if (PageAnon(head)) {
2268                 page_ref_inc(head);
2269         } else {
2270                 /* Additional pin to radix tree */
2271                 page_ref_add(head, 2);
2272                 spin_unlock(&head->mapping->tree_lock);
2273         }
2274 
2275         spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
2276 
2277         unfreeze_page(head);
2278 
2279         for (i = 0; i < HPAGE_PMD_NR; i++) {
2280                 struct page *subpage = head + i;
2281                 if (subpage == page)
2282                         continue;
2283                 unlock_page(subpage);
2284 
2285                 /*
2286                  * Subpages may be freed if there wasn't any mapping
2287                  * like if add_to_swap() is running on a lru page that
2288                  * had its mapping zapped. And freeing these pages
2289                  * requires taking the lru_lock so we do the put_page
2290                  * of the tail pages after the split is complete.
2291                  */
2292                 put_page(subpage);
2293         }
2294 }
2295 
2296 int total_mapcount(struct page *page)
2297 {
2298         int i, compound, ret;
2299 
2300         VM_BUG_ON_PAGE(PageTail(page), page);
2301 
2302         if (likely(!PageCompound(page)))
2303                 return atomic_read(&page->_mapcount) + 1;
2304 
2305         compound = compound_mapcount(page);
2306         if (PageHuge(page))
2307                 return compound;
2308         ret = compound;
2309         for (i = 0; i < HPAGE_PMD_NR; i++)
2310                 ret += atomic_read(&page[i]._mapcount) + 1;
2311         /* File pages has compound_mapcount included in _mapcount */
2312         if (!PageAnon(page))
2313                 return ret - compound * HPAGE_PMD_NR;
2314         if (PageDoubleMap(page))
2315                 ret -= HPAGE_PMD_NR;
2316         return ret;
2317 }
2318 
2319 /*
2320  * This calculates accurately how many mappings a transparent hugepage
2321  * has (unlike page_mapcount() which isn't fully accurate). This full
2322  * accuracy is primarily needed to know if copy-on-write faults can
2323  * reuse the page and change the mapping to read-write instead of
2324  * copying them. At the same time this returns the total_mapcount too.
2325  *
2326  * The function returns the highest mapcount any one of the subpages
2327  * has. If the return value is one, even if different processes are
2328  * mapping different subpages of the transparent hugepage, they can
2329  * all reuse it, because each process is reusing a different subpage.
2330  *
2331  * The total_mapcount is instead counting all virtual mappings of the
2332  * subpages. If the total_mapcount is equal to "one", it tells the
2333  * caller all mappings belong to the same "mm" and in turn the
2334  * anon_vma of the transparent hugepage can become the vma->anon_vma
2335  * local one as no other process may be mapping any of the subpages.
2336  *
2337  * It would be more accurate to replace page_mapcount() with
2338  * page_trans_huge_mapcount(), however we only use
2339  * page_trans_huge_mapcount() in the copy-on-write faults where we
2340  * need full accuracy to avoid breaking page pinning, because
2341  * page_trans_huge_mapcount() is slower than page_mapcount().
2342  */
2343 int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
2344 {
2345         int i, ret, _total_mapcount, mapcount;
2346 
2347         /* hugetlbfs shouldn't call it */
2348         VM_BUG_ON_PAGE(PageHuge(page), page);
2349 
2350         if (likely(!PageTransCompound(page))) {
2351                 mapcount = atomic_read(&page->_mapcount) + 1;
2352                 if (total_mapcount)
2353                         *total_mapcount = mapcount;
2354                 return mapcount;
2355         }
2356 
2357         page = compound_head(page);
2358 
2359         _total_mapcount = ret = 0;
2360         for (i = 0; i < HPAGE_PMD_NR; i++) {
2361                 mapcount = atomic_read(&page[i]._mapcount) + 1;
2362                 ret = max(ret, mapcount);
2363                 _total_mapcount += mapcount;
2364         }
2365         if (PageDoubleMap(page)) {
2366                 ret -= 1;
2367                 _total_mapcount -= HPAGE_PMD_NR;
2368         }
2369         mapcount = compound_mapcount(page);
2370         ret += mapcount;
2371         _total_mapcount += mapcount;
2372         if (total_mapcount)
2373                 *total_mapcount = _total_mapcount;
2374         return ret;
2375 }
2376 
2377 /*
2378  * This function splits huge page into normal pages. @page can point to any
2379  * subpage of huge page to split. Split doesn't change the position of @page.
2380  *
2381  * Only caller must hold pin on the @page, otherwise split fails with -EBUSY.
2382  * The huge page must be locked.
2383  *
2384  * If @list is null, tail pages will be added to LRU list, otherwise, to @list.
2385  *
2386  * Both head page and tail pages will inherit mapping, flags, and so on from
2387  * the hugepage.
2388  *
2389  * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if
2390  * they are not mapped.
2391  *
2392  * Returns 0 if the hugepage is split successfully.
2393  * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under
2394  * us.
2395  */
2396 int split_huge_page_to_list(struct page *page, struct list_head *list)
2397 {
2398         struct page *head = compound_head(page);
2399         struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
2400         struct anon_vma *anon_vma = NULL;
2401         struct address_space *mapping = NULL;
2402         int count, mapcount, extra_pins, ret;
2403         bool mlocked;
2404         unsigned long flags;
2405 
2406         VM_BUG_ON_PAGE(is_huge_zero_page(page), page);
2407         VM_BUG_ON_PAGE(!PageLocked(page), page);
2408         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
2409         VM_BUG_ON_PAGE(!PageCompound(page), page);
2410 
2411         if (PageAnon(head)) {
2412                 /*
2413                  * The caller does not necessarily hold an mmap_sem that would
2414                  * prevent the anon_vma disappearing so we first we take a
2415                  * reference to it and then lock the anon_vma for write. This
2416                  * is similar to page_lock_anon_vma_read except the write lock
2417                  * is taken to serialise against parallel split or collapse
2418                  * operations.
2419                  */
2420                 anon_vma = page_get_anon_vma(head);
2421                 if (!anon_vma) {
2422                         ret = -EBUSY;
2423                         goto out;
2424                 }
2425                 extra_pins = 0;
2426                 mapping = NULL;
2427                 anon_vma_lock_write(anon_vma);
2428         } else {
2429                 mapping = head->mapping;
2430 
2431                 /* Truncated ? */
2432                 if (!mapping) {
2433                         ret = -EBUSY;
2434                         goto out;
2435                 }
2436 
2437                 /* Addidional pins from radix tree */
2438                 extra_pins = HPAGE_PMD_NR;
2439                 anon_vma = NULL;
2440                 i_mmap_lock_read(mapping);
2441         }
2442 
2443         /*
2444          * Racy check if we can split the page, before freeze_page() will
2445          * split PMDs
2446          */
2447         if (total_mapcount(head) != page_count(head) - extra_pins - 1) {
2448                 ret = -EBUSY;
2449                 goto out_unlock;
2450         }
2451 
2452         mlocked = PageMlocked(page);
2453         freeze_page(head);
2454         VM_BUG_ON_PAGE(compound_mapcount(head), head);
2455 
2456         /* Make sure the page is not on per-CPU pagevec as it takes pin */
2457         if (mlocked)
2458                 lru_add_drain();
2459 
2460         /* prevent PageLRU to go away from under us, and freeze lru stats */
2461         spin_lock_irqsave(zone_lru_lock(page_zone(head)), flags);
2462 
2463         if (mapping) {
2464                 void **pslot;
2465 
2466                 spin_lock(&mapping->tree_lock);
2467                 pslot = radix_tree_lookup_slot(&mapping->page_tree,
2468                                 page_index(head));
2469                 /*
2470                  * Check if the head page is present in radix tree.
2471                  * We assume all tail are present too, if head is there.
2472                  */
2473                 if (radix_tree_deref_slot_protected(pslot,
2474                                         &mapping->tree_lock) != head)
2475                         goto fail;
2476         }
2477 
2478         /* Prevent deferred_split_scan() touching ->_refcount */
2479         spin_lock(&pgdata->split_queue_lock);
2480         count = page_count(head);
2481         mapcount = total_mapcount(head);
2482         if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
2483                 if (!list_empty(page_deferred_list(head))) {
2484                         pgdata->split_queue_len--;
2485                         list_del(page_deferred_list(head));
2486                 }
2487                 if (mapping)
2488                         __dec_node_page_state(page, NR_SHMEM_THPS);
2489                 spin_unlock(&pgdata->split_queue_lock);
2490                 __split_huge_page(page, list, flags);
2491                 ret = 0;
2492         } else {
2493                 if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
2494                         pr_alert("total_mapcount: %u, page_count(): %u\n",
2495                                         mapcount, count);
2496                         if (PageTail(page))
2497                                 dump_page(head, NULL);
2498                         dump_page(page, "total_mapcount(head) > 0");
2499                         BUG();
2500                 }
2501                 spin_unlock(&pgdata->split_queue_lock);
2502 fail:           if (mapping)
2503                         spin_unlock(&mapping->tree_lock);
2504                 spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
2505                 unfreeze_page(head);
2506                 ret = -EBUSY;
2507         }
2508 
2509 out_unlock:
2510         if (anon_vma) {
2511                 anon_vma_unlock_write(anon_vma);
2512                 put_anon_vma(anon_vma);
2513         }
2514         if (mapping)
2515                 i_mmap_unlock_read(mapping);
2516 out:
2517         count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
2518         return ret;
2519 }
2520 
2521 void free_transhuge_page(struct page *page)
2522 {
2523         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2524         unsigned long flags;
2525 
2526         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2527         if (!list_empty(page_deferred_list(page))) {
2528                 pgdata->split_queue_len--;
2529                 list_del(page_deferred_list(page));
2530         }
2531         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2532         free_compound_page(page);
2533 }
2534 
2535 void deferred_split_huge_page(struct page *page)
2536 {
2537         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2538         unsigned long flags;
2539 
2540         VM_BUG_ON_PAGE(!PageTransHuge(page), page);
2541 
2542         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2543         if (list_empty(page_deferred_list(page))) {
2544                 count_vm_event(THP_DEFERRED_SPLIT_PAGE);
2545                 list_add_tail(page_deferred_list(page), &pgdata->split_queue);
2546                 pgdata->split_queue_len++;
2547         }
2548         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2549 }
2550 
2551 static unsigned long deferred_split_count(struct shrinker *shrink,
2552                 struct shrink_control *sc)
2553 {
2554         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2555         return ACCESS_ONCE(pgdata->split_queue_len);
2556 }
2557 
2558 static unsigned long deferred_split_scan(struct shrinker *shrink,
2559                 struct shrink_control *sc)
2560 {
2561         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2562         unsigned long flags;
2563         LIST_HEAD(list), *pos, *next;
2564         struct page *page;
2565         int split = 0;
2566 
2567         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2568         /* Take pin on all head pages to avoid freeing them under us */
2569         list_for_each_safe(pos, next, &pgdata->split_queue) {
2570                 page = list_entry((void *)pos, struct page, mapping);
2571                 page = compound_head(page);
2572                 if (get_page_unless_zero(page)) {
2573                         list_move(page_deferred_list(page), &list);
2574                 } else {
2575                         /* We lost race with put_compound_page() */
2576                         list_del_init(page_deferred_list(page));
2577                         pgdata->split_queue_len--;
2578                 }
2579                 if (!--sc->nr_to_scan)
2580                         break;
2581         }
2582         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2583 
2584         list_for_each_safe(pos, next, &list) {
2585                 page = list_entry((void *)pos, struct page, mapping);
2586                 lock_page(page);
2587                 /* split_huge_page() removes page from list on success */
2588                 if (!split_huge_page(page))
2589                         split++;
2590                 unlock_page(page);
2591                 put_page(page);
2592         }
2593 
2594         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2595         list_splice_tail(&list, &pgdata->split_queue);
2596         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2597 
2598         /*
2599          * Stop shrinker if we didn't split any page, but the queue is empty.
2600          * This can happen if pages were freed under us.
2601          */
2602         if (!split && list_empty(&pgdata->split_queue))
2603                 return SHRINK_STOP;
2604         return split;
2605 }
2606 
2607 static struct shrinker deferred_split_shrinker = {
2608         .count_objects = deferred_split_count,
2609         .scan_objects = deferred_split_scan,
2610         .seeks = DEFAULT_SEEKS,
2611         .flags = SHRINKER_NUMA_AWARE,
2612 };
2613 
2614 #ifdef CONFIG_DEBUG_FS
2615 static int split_huge_pages_set(void *data, u64 val)
2616 {
2617         struct zone *zone;
2618         struct page *page;
2619         unsigned long pfn, max_zone_pfn;
2620         unsigned long total = 0, split = 0;
2621 
2622         if (val != 1)
2623                 return -EINVAL;
2624 
2625         for_each_populated_zone(zone) {
2626                 max_zone_pfn = zone_end_pfn(zone);
2627                 for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
2628                         if (!pfn_valid(pfn))
2629                                 continue;
2630 
2631                         page = pfn_to_page(pfn);
2632                         if (!get_page_unless_zero(page))
2633                                 continue;
2634 
2635                         if (zone != page_zone(page))
2636                                 goto next;
2637 
2638                         if (!PageHead(page) || PageHuge(page) || !PageLRU(page))
2639                                 goto next;
2640 
2641                         total++;
2642                         lock_page(page);
2643                         if (!split_huge_page(page))
2644                                 split++;
2645                         unlock_page(page);
2646 next:
2647                         put_page(page);
2648                 }
2649         }
2650 
2651         pr_info("%lu of %lu THP split\n", split, total);
2652 
2653         return 0;
2654 }
2655 DEFINE_SIMPLE_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
2656                 "%llu\n");
2657 
2658 static int __init split_huge_pages_debugfs(void)
2659 {
2660         void *ret;
2661 
2662         ret = debugfs_create_file("split_huge_pages", 0200, NULL, NULL,
2663                         &split_huge_pages_fops);
2664         if (!ret)
2665                 pr_warn("Failed to create split_huge_pages in debugfs");
2666         return 0;
2667 }
2668 late_initcall(split_huge_pages_debugfs);
2669 #endif
2670 

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