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Linux/mm/rmap.c

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  1 /*
  2  * mm/rmap.c - physical to virtual reverse mappings
  3  *
  4  * Copyright 2001, Rik van Riel <riel@conectiva.com.br>
  5  * Released under the General Public License (GPL).
  6  *
  7  * Simple, low overhead reverse mapping scheme.
  8  * Please try to keep this thing as modular as possible.
  9  *
 10  * Provides methods for unmapping each kind of mapped page:
 11  * the anon methods track anonymous pages, and
 12  * the file methods track pages belonging to an inode.
 13  *
 14  * Original design by Rik van Riel <riel@conectiva.com.br> 2001
 15  * File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004
 16  * Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004
 17  * Contributions by Hugh Dickins 2003, 2004
 18  */
 19 
 20 /*
 21  * Lock ordering in mm:
 22  *
 23  * inode->i_mutex       (while writing or truncating, not reading or faulting)
 24  *   mm->mmap_sem
 25  *     page->flags PG_locked (lock_page)
 26  *       hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share)
 27  *         mapping->i_mmap_rwsem
 28  *           anon_vma->rwsem
 29  *             mm->page_table_lock or pte_lock
 30  *               zone_lru_lock (in mark_page_accessed, isolate_lru_page)
 31  *               swap_lock (in swap_duplicate, swap_info_get)
 32  *                 mmlist_lock (in mmput, drain_mmlist and others)
 33  *                 mapping->private_lock (in __set_page_dirty_buffers)
 34  *                   mem_cgroup_{begin,end}_page_stat (memcg->move_lock)
 35  *                     i_pages lock (widely used)
 36  *                 inode->i_lock (in set_page_dirty's __mark_inode_dirty)
 37  *                 bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
 38  *                   sb_lock (within inode_lock in fs/fs-writeback.c)
 39  *                   i_pages lock (widely used, in set_page_dirty,
 40  *                             in arch-dependent flush_dcache_mmap_lock,
 41  *                             within bdi.wb->list_lock in __sync_single_inode)
 42  *
 43  * anon_vma->rwsem,mapping->i_mutex      (memory_failure, collect_procs_anon)
 44  *   ->tasklist_lock
 45  *     pte map lock
 46  */
 47 
 48 #include <linux/mm.h>
 49 #include <linux/sched/mm.h>
 50 #include <linux/sched/task.h>
 51 #include <linux/pagemap.h>
 52 #include <linux/swap.h>
 53 #include <linux/swapops.h>
 54 #include <linux/slab.h>
 55 #include <linux/init.h>
 56 #include <linux/ksm.h>
 57 #include <linux/rmap.h>
 58 #include <linux/rcupdate.h>
 59 #include <linux/export.h>
 60 #include <linux/memcontrol.h>
 61 #include <linux/mmu_notifier.h>
 62 #include <linux/migrate.h>
 63 #include <linux/hugetlb.h>
 64 #include <linux/backing-dev.h>
 65 #include <linux/page_idle.h>
 66 #include <linux/memremap.h>
 67 #include <linux/userfaultfd_k.h>
 68 
 69 #include <asm/tlbflush.h>
 70 
 71 #include <trace/events/tlb.h>
 72 
 73 #include "internal.h"
 74 
 75 static struct kmem_cache *anon_vma_cachep;
 76 static struct kmem_cache *anon_vma_chain_cachep;
 77 
 78 static inline struct anon_vma *anon_vma_alloc(void)
 79 {
 80         struct anon_vma *anon_vma;
 81 
 82         anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
 83         if (anon_vma) {
 84                 atomic_set(&anon_vma->refcount, 1);
 85                 anon_vma->degree = 1;   /* Reference for first vma */
 86                 anon_vma->parent = anon_vma;
 87                 /*
 88                  * Initialise the anon_vma root to point to itself. If called
 89                  * from fork, the root will be reset to the parents anon_vma.
 90                  */
 91                 anon_vma->root = anon_vma;
 92         }
 93 
 94         return anon_vma;
 95 }
 96 
 97 static inline void anon_vma_free(struct anon_vma *anon_vma)
 98 {
 99         VM_BUG_ON(atomic_read(&anon_vma->refcount));
100 
101         /*
102          * Synchronize against page_lock_anon_vma_read() such that
103          * we can safely hold the lock without the anon_vma getting
104          * freed.
105          *
106          * Relies on the full mb implied by the atomic_dec_and_test() from
107          * put_anon_vma() against the acquire barrier implied by
108          * down_read_trylock() from page_lock_anon_vma_read(). This orders:
109          *
110          * page_lock_anon_vma_read()    VS      put_anon_vma()
111          *   down_read_trylock()                  atomic_dec_and_test()
112          *   LOCK                                 MB
113          *   atomic_read()                        rwsem_is_locked()
114          *
115          * LOCK should suffice since the actual taking of the lock must
116          * happen _before_ what follows.
117          */
118         might_sleep();
119         if (rwsem_is_locked(&anon_vma->root->rwsem)) {
120                 anon_vma_lock_write(anon_vma);
121                 anon_vma_unlock_write(anon_vma);
122         }
123 
124         kmem_cache_free(anon_vma_cachep, anon_vma);
125 }
126 
127 static inline struct anon_vma_chain *anon_vma_chain_alloc(gfp_t gfp)
128 {
129         return kmem_cache_alloc(anon_vma_chain_cachep, gfp);
130 }
131 
132 static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
133 {
134         kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain);
135 }
136 
137 static void anon_vma_chain_link(struct vm_area_struct *vma,
138                                 struct anon_vma_chain *avc,
139                                 struct anon_vma *anon_vma)
140 {
141         avc->vma = vma;
142         avc->anon_vma = anon_vma;
143         list_add(&avc->same_vma, &vma->anon_vma_chain);
144         anon_vma_interval_tree_insert(avc, &anon_vma->rb_root);
145 }
146 
147 /**
148  * __anon_vma_prepare - attach an anon_vma to a memory region
149  * @vma: the memory region in question
150  *
151  * This makes sure the memory mapping described by 'vma' has
152  * an 'anon_vma' attached to it, so that we can associate the
153  * anonymous pages mapped into it with that anon_vma.
154  *
155  * The common case will be that we already have one, which
156  * is handled inline by anon_vma_prepare(). But if
157  * not we either need to find an adjacent mapping that we
158  * can re-use the anon_vma from (very common when the only
159  * reason for splitting a vma has been mprotect()), or we
160  * allocate a new one.
161  *
162  * Anon-vma allocations are very subtle, because we may have
163  * optimistically looked up an anon_vma in page_lock_anon_vma_read()
164  * and that may actually touch the spinlock even in the newly
165  * allocated vma (it depends on RCU to make sure that the
166  * anon_vma isn't actually destroyed).
167  *
168  * As a result, we need to do proper anon_vma locking even
169  * for the new allocation. At the same time, we do not want
170  * to do any locking for the common case of already having
171  * an anon_vma.
172  *
173  * This must be called with the mmap_sem held for reading.
174  */
175 int __anon_vma_prepare(struct vm_area_struct *vma)
176 {
177         struct mm_struct *mm = vma->vm_mm;
178         struct anon_vma *anon_vma, *allocated;
179         struct anon_vma_chain *avc;
180 
181         might_sleep();
182 
183         avc = anon_vma_chain_alloc(GFP_KERNEL);
184         if (!avc)
185                 goto out_enomem;
186 
187         anon_vma = find_mergeable_anon_vma(vma);
188         allocated = NULL;
189         if (!anon_vma) {
190                 anon_vma = anon_vma_alloc();
191                 if (unlikely(!anon_vma))
192                         goto out_enomem_free_avc;
193                 allocated = anon_vma;
194         }
195 
196         anon_vma_lock_write(anon_vma);
197         /* page_table_lock to protect against threads */
198         spin_lock(&mm->page_table_lock);
199         if (likely(!vma->anon_vma)) {
200                 vma->anon_vma = anon_vma;
201                 anon_vma_chain_link(vma, avc, anon_vma);
202                 /* vma reference or self-parent link for new root */
203                 anon_vma->degree++;
204                 allocated = NULL;
205                 avc = NULL;
206         }
207         spin_unlock(&mm->page_table_lock);
208         anon_vma_unlock_write(anon_vma);
209 
210         if (unlikely(allocated))
211                 put_anon_vma(allocated);
212         if (unlikely(avc))
213                 anon_vma_chain_free(avc);
214 
215         return 0;
216 
217  out_enomem_free_avc:
218         anon_vma_chain_free(avc);
219  out_enomem:
220         return -ENOMEM;
221 }
222 
223 /*
224  * This is a useful helper function for locking the anon_vma root as
225  * we traverse the vma->anon_vma_chain, looping over anon_vma's that
226  * have the same vma.
227  *
228  * Such anon_vma's should have the same root, so you'd expect to see
229  * just a single mutex_lock for the whole traversal.
230  */
231 static inline struct anon_vma *lock_anon_vma_root(struct anon_vma *root, struct anon_vma *anon_vma)
232 {
233         struct anon_vma *new_root = anon_vma->root;
234         if (new_root != root) {
235                 if (WARN_ON_ONCE(root))
236                         up_write(&root->rwsem);
237                 root = new_root;
238                 down_write(&root->rwsem);
239         }
240         return root;
241 }
242 
243 static inline void unlock_anon_vma_root(struct anon_vma *root)
244 {
245         if (root)
246                 up_write(&root->rwsem);
247 }
248 
249 /*
250  * Attach the anon_vmas from src to dst.
251  * Returns 0 on success, -ENOMEM on failure.
252  *
253  * If dst->anon_vma is NULL this function tries to find and reuse existing
254  * anon_vma which has no vmas and only one child anon_vma. This prevents
255  * degradation of anon_vma hierarchy to endless linear chain in case of
256  * constantly forking task. On the other hand, an anon_vma with more than one
257  * child isn't reused even if there was no alive vma, thus rmap walker has a
258  * good chance of avoiding scanning the whole hierarchy when it searches where
259  * page is mapped.
260  */
261 int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
262 {
263         struct anon_vma_chain *avc, *pavc;
264         struct anon_vma *root = NULL;
265 
266         list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
267                 struct anon_vma *anon_vma;
268 
269                 avc = anon_vma_chain_alloc(GFP_NOWAIT | __GFP_NOWARN);
270                 if (unlikely(!avc)) {
271                         unlock_anon_vma_root(root);
272                         root = NULL;
273                         avc = anon_vma_chain_alloc(GFP_KERNEL);
274                         if (!avc)
275                                 goto enomem_failure;
276                 }
277                 anon_vma = pavc->anon_vma;
278                 root = lock_anon_vma_root(root, anon_vma);
279                 anon_vma_chain_link(dst, avc, anon_vma);
280 
281                 /*
282                  * Reuse existing anon_vma if its degree lower than two,
283                  * that means it has no vma and only one anon_vma child.
284                  *
285                  * Do not chose parent anon_vma, otherwise first child
286                  * will always reuse it. Root anon_vma is never reused:
287                  * it has self-parent reference and at least one child.
288                  */
289                 if (!dst->anon_vma && anon_vma != src->anon_vma &&
290                                 anon_vma->degree < 2)
291                         dst->anon_vma = anon_vma;
292         }
293         if (dst->anon_vma)
294                 dst->anon_vma->degree++;
295         unlock_anon_vma_root(root);
296         return 0;
297 
298  enomem_failure:
299         /*
300          * dst->anon_vma is dropped here otherwise its degree can be incorrectly
301          * decremented in unlink_anon_vmas().
302          * We can safely do this because callers of anon_vma_clone() don't care
303          * about dst->anon_vma if anon_vma_clone() failed.
304          */
305         dst->anon_vma = NULL;
306         unlink_anon_vmas(dst);
307         return -ENOMEM;
308 }
309 
310 /*
311  * Attach vma to its own anon_vma, as well as to the anon_vmas that
312  * the corresponding VMA in the parent process is attached to.
313  * Returns 0 on success, non-zero on failure.
314  */
315 int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
316 {
317         struct anon_vma_chain *avc;
318         struct anon_vma *anon_vma;
319         int error;
320 
321         /* Don't bother if the parent process has no anon_vma here. */
322         if (!pvma->anon_vma)
323                 return 0;
324 
325         /* Drop inherited anon_vma, we'll reuse existing or allocate new. */
326         vma->anon_vma = NULL;
327 
328         /*
329          * First, attach the new VMA to the parent VMA's anon_vmas,
330          * so rmap can find non-COWed pages in child processes.
331          */
332         error = anon_vma_clone(vma, pvma);
333         if (error)
334                 return error;
335 
336         /* An existing anon_vma has been reused, all done then. */
337         if (vma->anon_vma)
338                 return 0;
339 
340         /* Then add our own anon_vma. */
341         anon_vma = anon_vma_alloc();
342         if (!anon_vma)
343                 goto out_error;
344         avc = anon_vma_chain_alloc(GFP_KERNEL);
345         if (!avc)
346                 goto out_error_free_anon_vma;
347 
348         /*
349          * The root anon_vma's spinlock is the lock actually used when we
350          * lock any of the anon_vmas in this anon_vma tree.
351          */
352         anon_vma->root = pvma->anon_vma->root;
353         anon_vma->parent = pvma->anon_vma;
354         /*
355          * With refcounts, an anon_vma can stay around longer than the
356          * process it belongs to. The root anon_vma needs to be pinned until
357          * this anon_vma is freed, because the lock lives in the root.
358          */
359         get_anon_vma(anon_vma->root);
360         /* Mark this anon_vma as the one where our new (COWed) pages go. */
361         vma->anon_vma = anon_vma;
362         anon_vma_lock_write(anon_vma);
363         anon_vma_chain_link(vma, avc, anon_vma);
364         anon_vma->parent->degree++;
365         anon_vma_unlock_write(anon_vma);
366 
367         return 0;
368 
369  out_error_free_anon_vma:
370         put_anon_vma(anon_vma);
371  out_error:
372         unlink_anon_vmas(vma);
373         return -ENOMEM;
374 }
375 
376 void unlink_anon_vmas(struct vm_area_struct *vma)
377 {
378         struct anon_vma_chain *avc, *next;
379         struct anon_vma *root = NULL;
380 
381         /*
382          * Unlink each anon_vma chained to the VMA.  This list is ordered
383          * from newest to oldest, ensuring the root anon_vma gets freed last.
384          */
385         list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
386                 struct anon_vma *anon_vma = avc->anon_vma;
387 
388                 root = lock_anon_vma_root(root, anon_vma);
389                 anon_vma_interval_tree_remove(avc, &anon_vma->rb_root);
390 
391                 /*
392                  * Leave empty anon_vmas on the list - we'll need
393                  * to free them outside the lock.
394                  */
395                 if (RB_EMPTY_ROOT(&anon_vma->rb_root.rb_root)) {
396                         anon_vma->parent->degree--;
397                         continue;
398                 }
399 
400                 list_del(&avc->same_vma);
401                 anon_vma_chain_free(avc);
402         }
403         if (vma->anon_vma)
404                 vma->anon_vma->degree--;
405         unlock_anon_vma_root(root);
406 
407         /*
408          * Iterate the list once more, it now only contains empty and unlinked
409          * anon_vmas, destroy them. Could not do before due to __put_anon_vma()
410          * needing to write-acquire the anon_vma->root->rwsem.
411          */
412         list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
413                 struct anon_vma *anon_vma = avc->anon_vma;
414 
415                 VM_WARN_ON(anon_vma->degree);
416                 put_anon_vma(anon_vma);
417 
418                 list_del(&avc->same_vma);
419                 anon_vma_chain_free(avc);
420         }
421 }
422 
423 static void anon_vma_ctor(void *data)
424 {
425         struct anon_vma *anon_vma = data;
426 
427         init_rwsem(&anon_vma->rwsem);
428         atomic_set(&anon_vma->refcount, 0);
429         anon_vma->rb_root = RB_ROOT_CACHED;
430 }
431 
432 void __init anon_vma_init(void)
433 {
434         anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
435                         0, SLAB_TYPESAFE_BY_RCU|SLAB_PANIC|SLAB_ACCOUNT,
436                         anon_vma_ctor);
437         anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain,
438                         SLAB_PANIC|SLAB_ACCOUNT);
439 }
440 
441 /*
442  * Getting a lock on a stable anon_vma from a page off the LRU is tricky!
443  *
444  * Since there is no serialization what so ever against page_remove_rmap()
445  * the best this function can do is return a locked anon_vma that might
446  * have been relevant to this page.
447  *
448  * The page might have been remapped to a different anon_vma or the anon_vma
449  * returned may already be freed (and even reused).
450  *
451  * In case it was remapped to a different anon_vma, the new anon_vma will be a
452  * child of the old anon_vma, and the anon_vma lifetime rules will therefore
453  * ensure that any anon_vma obtained from the page will still be valid for as
454  * long as we observe page_mapped() [ hence all those page_mapped() tests ].
455  *
456  * All users of this function must be very careful when walking the anon_vma
457  * chain and verify that the page in question is indeed mapped in it
458  * [ something equivalent to page_mapped_in_vma() ].
459  *
460  * Since anon_vma's slab is DESTROY_BY_RCU and we know from page_remove_rmap()
461  * that the anon_vma pointer from page->mapping is valid if there is a
462  * mapcount, we can dereference the anon_vma after observing those.
463  */
464 struct anon_vma *page_get_anon_vma(struct page *page)
465 {
466         struct anon_vma *anon_vma = NULL;
467         unsigned long anon_mapping;
468 
469         rcu_read_lock();
470         anon_mapping = (unsigned long)READ_ONCE(page->mapping);
471         if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
472                 goto out;
473         if (!page_mapped(page))
474                 goto out;
475 
476         anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
477         if (!atomic_inc_not_zero(&anon_vma->refcount)) {
478                 anon_vma = NULL;
479                 goto out;
480         }
481 
482         /*
483          * If this page is still mapped, then its anon_vma cannot have been
484          * freed.  But if it has been unmapped, we have no security against the
485          * anon_vma structure being freed and reused (for another anon_vma:
486          * SLAB_TYPESAFE_BY_RCU guarantees that - so the atomic_inc_not_zero()
487          * above cannot corrupt).
488          */
489         if (!page_mapped(page)) {
490                 rcu_read_unlock();
491                 put_anon_vma(anon_vma);
492                 return NULL;
493         }
494 out:
495         rcu_read_unlock();
496 
497         return anon_vma;
498 }
499 
500 /*
501  * Similar to page_get_anon_vma() except it locks the anon_vma.
502  *
503  * Its a little more complex as it tries to keep the fast path to a single
504  * atomic op -- the trylock. If we fail the trylock, we fall back to getting a
505  * reference like with page_get_anon_vma() and then block on the mutex.
506  */
507 struct anon_vma *page_lock_anon_vma_read(struct page *page)
508 {
509         struct anon_vma *anon_vma = NULL;
510         struct anon_vma *root_anon_vma;
511         unsigned long anon_mapping;
512 
513         rcu_read_lock();
514         anon_mapping = (unsigned long)READ_ONCE(page->mapping);
515         if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
516                 goto out;
517         if (!page_mapped(page))
518                 goto out;
519 
520         anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
521         root_anon_vma = READ_ONCE(anon_vma->root);
522         if (down_read_trylock(&root_anon_vma->rwsem)) {
523                 /*
524                  * If the page is still mapped, then this anon_vma is still
525                  * its anon_vma, and holding the mutex ensures that it will
526                  * not go away, see anon_vma_free().
527                  */
528                 if (!page_mapped(page)) {
529                         up_read(&root_anon_vma->rwsem);
530                         anon_vma = NULL;
531                 }
532                 goto out;
533         }
534 
535         /* trylock failed, we got to sleep */
536         if (!atomic_inc_not_zero(&anon_vma->refcount)) {
537                 anon_vma = NULL;
538                 goto out;
539         }
540 
541         if (!page_mapped(page)) {
542                 rcu_read_unlock();
543                 put_anon_vma(anon_vma);
544                 return NULL;
545         }
546 
547         /* we pinned the anon_vma, its safe to sleep */
548         rcu_read_unlock();
549         anon_vma_lock_read(anon_vma);
550 
551         if (atomic_dec_and_test(&anon_vma->refcount)) {
552                 /*
553                  * Oops, we held the last refcount, release the lock
554                  * and bail -- can't simply use put_anon_vma() because
555                  * we'll deadlock on the anon_vma_lock_write() recursion.
556                  */
557                 anon_vma_unlock_read(anon_vma);
558                 __put_anon_vma(anon_vma);
559                 anon_vma = NULL;
560         }
561 
562         return anon_vma;
563 
564 out:
565         rcu_read_unlock();
566         return anon_vma;
567 }
568 
569 void page_unlock_anon_vma_read(struct anon_vma *anon_vma)
570 {
571         anon_vma_unlock_read(anon_vma);
572 }
573 
574 #ifdef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
575 /*
576  * Flush TLB entries for recently unmapped pages from remote CPUs. It is
577  * important if a PTE was dirty when it was unmapped that it's flushed
578  * before any IO is initiated on the page to prevent lost writes. Similarly,
579  * it must be flushed before freeing to prevent data leakage.
580  */
581 void try_to_unmap_flush(void)
582 {
583         struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
584 
585         if (!tlb_ubc->flush_required)
586                 return;
587 
588         arch_tlbbatch_flush(&tlb_ubc->arch);
589         tlb_ubc->flush_required = false;
590         tlb_ubc->writable = false;
591 }
592 
593 /* Flush iff there are potentially writable TLB entries that can race with IO */
594 void try_to_unmap_flush_dirty(void)
595 {
596         struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
597 
598         if (tlb_ubc->writable)
599                 try_to_unmap_flush();
600 }
601 
602 static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)
603 {
604         struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
605 
606         arch_tlbbatch_add_mm(&tlb_ubc->arch, mm);
607         tlb_ubc->flush_required = true;
608 
609         /*
610          * Ensure compiler does not re-order the setting of tlb_flush_batched
611          * before the PTE is cleared.
612          */
613         barrier();
614         mm->tlb_flush_batched = true;
615 
616         /*
617          * If the PTE was dirty then it's best to assume it's writable. The
618          * caller must use try_to_unmap_flush_dirty() or try_to_unmap_flush()
619          * before the page is queued for IO.
620          */
621         if (writable)
622                 tlb_ubc->writable = true;
623 }
624 
625 /*
626  * Returns true if the TLB flush should be deferred to the end of a batch of
627  * unmap operations to reduce IPIs.
628  */
629 static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
630 {
631         bool should_defer = false;
632 
633         if (!(flags & TTU_BATCH_FLUSH))
634                 return false;
635 
636         /* If remote CPUs need to be flushed then defer batch the flush */
637         if (cpumask_any_but(mm_cpumask(mm), get_cpu()) < nr_cpu_ids)
638                 should_defer = true;
639         put_cpu();
640 
641         return should_defer;
642 }
643 
644 /*
645  * Reclaim unmaps pages under the PTL but do not flush the TLB prior to
646  * releasing the PTL if TLB flushes are batched. It's possible for a parallel
647  * operation such as mprotect or munmap to race between reclaim unmapping
648  * the page and flushing the page. If this race occurs, it potentially allows
649  * access to data via a stale TLB entry. Tracking all mm's that have TLB
650  * batching in flight would be expensive during reclaim so instead track
651  * whether TLB batching occurred in the past and if so then do a flush here
652  * if required. This will cost one additional flush per reclaim cycle paid
653  * by the first operation at risk such as mprotect and mumap.
654  *
655  * This must be called under the PTL so that an access to tlb_flush_batched
656  * that is potentially a "reclaim vs mprotect/munmap/etc" race will synchronise
657  * via the PTL.
658  */
659 void flush_tlb_batched_pending(struct mm_struct *mm)
660 {
661         if (mm->tlb_flush_batched) {
662                 flush_tlb_mm(mm);
663 
664                 /*
665                  * Do not allow the compiler to re-order the clearing of
666                  * tlb_flush_batched before the tlb is flushed.
667                  */
668                 barrier();
669                 mm->tlb_flush_batched = false;
670         }
671 }
672 #else
673 static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)
674 {
675 }
676 
677 static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
678 {
679         return false;
680 }
681 #endif /* CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH */
682 
683 /*
684  * At what user virtual address is page expected in vma?
685  * Caller should check the page is actually part of the vma.
686  */
687 unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
688 {
689         unsigned long address;
690         if (PageAnon(page)) {
691                 struct anon_vma *page__anon_vma = page_anon_vma(page);
692                 /*
693                  * Note: swapoff's unuse_vma() is more efficient with this
694                  * check, and needs it to match anon_vma when KSM is active.
695                  */
696                 if (!vma->anon_vma || !page__anon_vma ||
697                     vma->anon_vma->root != page__anon_vma->root)
698                         return -EFAULT;
699         } else if (page->mapping) {
700                 if (!vma->vm_file || vma->vm_file->f_mapping != page->mapping)
701                         return -EFAULT;
702         } else
703                 return -EFAULT;
704         address = __vma_address(page, vma);
705         if (unlikely(address < vma->vm_start || address >= vma->vm_end))
706                 return -EFAULT;
707         return address;
708 }
709 
710 pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
711 {
712         pgd_t *pgd;
713         p4d_t *p4d;
714         pud_t *pud;
715         pmd_t *pmd = NULL;
716         pmd_t pmde;
717 
718         pgd = pgd_offset(mm, address);
719         if (!pgd_present(*pgd))
720                 goto out;
721 
722         p4d = p4d_offset(pgd, address);
723         if (!p4d_present(*p4d))
724                 goto out;
725 
726         pud = pud_offset(p4d, address);
727         if (!pud_present(*pud))
728                 goto out;
729 
730         pmd = pmd_offset(pud, address);
731         /*
732          * Some THP functions use the sequence pmdp_huge_clear_flush(), set_pmd_at()
733          * without holding anon_vma lock for write.  So when looking for a
734          * genuine pmde (in which to find pte), test present and !THP together.
735          */
736         pmde = *pmd;
737         barrier();
738         if (!pmd_present(pmde) || pmd_trans_huge(pmde))
739                 pmd = NULL;
740 out:
741         return pmd;
742 }
743 
744 struct page_referenced_arg {
745         int mapcount;
746         int referenced;
747         unsigned long vm_flags;
748         struct mem_cgroup *memcg;
749 };
750 /*
751  * arg: page_referenced_arg will be passed
752  */
753 static bool page_referenced_one(struct page *page, struct vm_area_struct *vma,
754                         unsigned long address, void *arg)
755 {
756         struct page_referenced_arg *pra = arg;
757         struct page_vma_mapped_walk pvmw = {
758                 .page = page,
759                 .vma = vma,
760                 .address = address,
761         };
762         int referenced = 0;
763 
764         while (page_vma_mapped_walk(&pvmw)) {
765                 address = pvmw.address;
766 
767                 if (vma->vm_flags & VM_LOCKED) {
768                         page_vma_mapped_walk_done(&pvmw);
769                         pra->vm_flags |= VM_LOCKED;
770                         return false; /* To break the loop */
771                 }
772 
773                 if (pvmw.pte) {
774                         if (ptep_clear_flush_young_notify(vma, address,
775                                                 pvmw.pte)) {
776                                 /*
777                                  * Don't treat a reference through
778                                  * a sequentially read mapping as such.
779                                  * If the page has been used in another mapping,
780                                  * we will catch it; if this other mapping is
781                                  * already gone, the unmap path will have set
782                                  * PG_referenced or activated the page.
783                                  */
784                                 if (likely(!(vma->vm_flags & VM_SEQ_READ)))
785                                         referenced++;
786                         }
787                 } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
788                         if (pmdp_clear_flush_young_notify(vma, address,
789                                                 pvmw.pmd))
790                                 referenced++;
791                 } else {
792                         /* unexpected pmd-mapped page? */
793                         WARN_ON_ONCE(1);
794                 }
795 
796                 pra->mapcount--;
797         }
798 
799         if (referenced)
800                 clear_page_idle(page);
801         if (test_and_clear_page_young(page))
802                 referenced++;
803 
804         if (referenced) {
805                 pra->referenced++;
806                 pra->vm_flags |= vma->vm_flags;
807         }
808 
809         if (!pra->mapcount)
810                 return false; /* To break the loop */
811 
812         return true;
813 }
814 
815 static bool invalid_page_referenced_vma(struct vm_area_struct *vma, void *arg)
816 {
817         struct page_referenced_arg *pra = arg;
818         struct mem_cgroup *memcg = pra->memcg;
819 
820         if (!mm_match_cgroup(vma->vm_mm, memcg))
821                 return true;
822 
823         return false;
824 }
825 
826 /**
827  * page_referenced - test if the page was referenced
828  * @page: the page to test
829  * @is_locked: caller holds lock on the page
830  * @memcg: target memory cgroup
831  * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
832  *
833  * Quick test_and_clear_referenced for all mappings to a page,
834  * returns the number of ptes which referenced the page.
835  */
836 int page_referenced(struct page *page,
837                     int is_locked,
838                     struct mem_cgroup *memcg,
839                     unsigned long *vm_flags)
840 {
841         int we_locked = 0;
842         struct page_referenced_arg pra = {
843                 .mapcount = total_mapcount(page),
844                 .memcg = memcg,
845         };
846         struct rmap_walk_control rwc = {
847                 .rmap_one = page_referenced_one,
848                 .arg = (void *)&pra,
849                 .anon_lock = page_lock_anon_vma_read,
850         };
851 
852         *vm_flags = 0;
853         if (!page_mapped(page))
854                 return 0;
855 
856         if (!page_rmapping(page))
857                 return 0;
858 
859         if (!is_locked && (!PageAnon(page) || PageKsm(page))) {
860                 we_locked = trylock_page(page);
861                 if (!we_locked)
862                         return 1;
863         }
864 
865         /*
866          * If we are reclaiming on behalf of a cgroup, skip
867          * counting on behalf of references from different
868          * cgroups
869          */
870         if (memcg) {
871                 rwc.invalid_vma = invalid_page_referenced_vma;
872         }
873 
874         rmap_walk(page, &rwc);
875         *vm_flags = pra.vm_flags;
876 
877         if (we_locked)
878                 unlock_page(page);
879 
880         return pra.referenced;
881 }
882 
883 static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma,
884                             unsigned long address, void *arg)
885 {
886         struct page_vma_mapped_walk pvmw = {
887                 .page = page,
888                 .vma = vma,
889                 .address = address,
890                 .flags = PVMW_SYNC,
891         };
892         unsigned long start = address, end;
893         int *cleaned = arg;
894 
895         /*
896          * We have to assume the worse case ie pmd for invalidation. Note that
897          * the page can not be free from this function.
898          */
899         end = min(vma->vm_end, start + (PAGE_SIZE << compound_order(page)));
900         mmu_notifier_invalidate_range_start(vma->vm_mm, start, end);
901 
902         while (page_vma_mapped_walk(&pvmw)) {
903                 unsigned long cstart;
904                 int ret = 0;
905 
906                 cstart = address = pvmw.address;
907                 if (pvmw.pte) {
908                         pte_t entry;
909                         pte_t *pte = pvmw.pte;
910 
911                         if (!pte_dirty(*pte) && !pte_write(*pte))
912                                 continue;
913 
914                         flush_cache_page(vma, address, pte_pfn(*pte));
915                         entry = ptep_clear_flush(vma, address, pte);
916                         entry = pte_wrprotect(entry);
917                         entry = pte_mkclean(entry);
918                         set_pte_at(vma->vm_mm, address, pte, entry);
919                         ret = 1;
920                 } else {
921 #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
922                         pmd_t *pmd = pvmw.pmd;
923                         pmd_t entry;
924 
925                         if (!pmd_dirty(*pmd) && !pmd_write(*pmd))
926                                 continue;
927 
928                         flush_cache_page(vma, address, page_to_pfn(page));
929                         entry = pmdp_huge_clear_flush(vma, address, pmd);
930                         entry = pmd_wrprotect(entry);
931                         entry = pmd_mkclean(entry);
932                         set_pmd_at(vma->vm_mm, address, pmd, entry);
933                         cstart &= PMD_MASK;
934                         ret = 1;
935 #else
936                         /* unexpected pmd-mapped page? */
937                         WARN_ON_ONCE(1);
938 #endif
939                 }
940 
941                 /*
942                  * No need to call mmu_notifier_invalidate_range() as we are
943                  * downgrading page table protection not changing it to point
944                  * to a new page.
945                  *
946                  * See Documentation/vm/mmu_notifier.rst
947                  */
948                 if (ret)
949                         (*cleaned)++;
950         }
951 
952         mmu_notifier_invalidate_range_end(vma->vm_mm, start, end);
953 
954         return true;
955 }
956 
957 static bool invalid_mkclean_vma(struct vm_area_struct *vma, void *arg)
958 {
959         if (vma->vm_flags & VM_SHARED)
960                 return false;
961 
962         return true;
963 }
964 
965 int page_mkclean(struct page *page)
966 {
967         int cleaned = 0;
968         struct address_space *mapping;
969         struct rmap_walk_control rwc = {
970                 .arg = (void *)&cleaned,
971                 .rmap_one = page_mkclean_one,
972                 .invalid_vma = invalid_mkclean_vma,
973         };
974 
975         BUG_ON(!PageLocked(page));
976 
977         if (!page_mapped(page))
978                 return 0;
979 
980         mapping = page_mapping(page);
981         if (!mapping)
982                 return 0;
983 
984         rmap_walk(page, &rwc);
985 
986         return cleaned;
987 }
988 EXPORT_SYMBOL_GPL(page_mkclean);
989 
990 /**
991  * page_move_anon_rmap - move a page to our anon_vma
992  * @page:       the page to move to our anon_vma
993  * @vma:        the vma the page belongs to
994  *
995  * When a page belongs exclusively to one process after a COW event,
996  * that page can be moved into the anon_vma that belongs to just that
997  * process, so the rmap code will not search the parent or sibling
998  * processes.
999  */
1000 void page_move_anon_rmap(struct page *page, struct vm_area_struct *vma)
1001 {
1002         struct anon_vma *anon_vma = vma->anon_vma;
1003 
1004         page = compound_head(page);
1005 
1006         VM_BUG_ON_PAGE(!PageLocked(page), page);
1007         VM_BUG_ON_VMA(!anon_vma, vma);
1008 
1009         anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1010         /*
1011          * Ensure that anon_vma and the PAGE_MAPPING_ANON bit are written
1012          * simultaneously, so a concurrent reader (eg page_referenced()'s
1013          * PageAnon()) will not see one without the other.
1014          */
1015         WRITE_ONCE(page->mapping, (struct address_space *) anon_vma);
1016 }
1017 
1018 /**
1019  * __page_set_anon_rmap - set up new anonymous rmap
1020  * @page:       Page to add to rmap     
1021  * @vma:        VM area to add page to.
1022  * @address:    User virtual address of the mapping     
1023  * @exclusive:  the page is exclusively owned by the current process
1024  */
1025 static void __page_set_anon_rmap(struct page *page,
1026         struct vm_area_struct *vma, unsigned long address, int exclusive)
1027 {
1028         struct anon_vma *anon_vma = vma->anon_vma;
1029 
1030         BUG_ON(!anon_vma);
1031 
1032         if (PageAnon(page))
1033                 return;
1034 
1035         /*
1036          * If the page isn't exclusively mapped into this vma,
1037          * we must use the _oldest_ possible anon_vma for the
1038          * page mapping!
1039          */
1040         if (!exclusive)
1041                 anon_vma = anon_vma->root;
1042 
1043         anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1044         page->mapping = (struct address_space *) anon_vma;
1045         page->index = linear_page_index(vma, address);
1046 }
1047 
1048 /**
1049  * __page_check_anon_rmap - sanity check anonymous rmap addition
1050  * @page:       the page to add the mapping to
1051  * @vma:        the vm area in which the mapping is added
1052  * @address:    the user virtual address mapped
1053  */
1054 static void __page_check_anon_rmap(struct page *page,
1055         struct vm_area_struct *vma, unsigned long address)
1056 {
1057 #ifdef CONFIG_DEBUG_VM
1058         /*
1059          * The page's anon-rmap details (mapping and index) are guaranteed to
1060          * be set up correctly at this point.
1061          *
1062          * We have exclusion against page_add_anon_rmap because the caller
1063          * always holds the page locked, except if called from page_dup_rmap,
1064          * in which case the page is already known to be setup.
1065          *
1066          * We have exclusion against page_add_new_anon_rmap because those pages
1067          * are initially only visible via the pagetables, and the pte is locked
1068          * over the call to page_add_new_anon_rmap.
1069          */
1070         BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root);
1071         BUG_ON(page_to_pgoff(page) != linear_page_index(vma, address));
1072 #endif
1073 }
1074 
1075 /**
1076  * page_add_anon_rmap - add pte mapping to an anonymous page
1077  * @page:       the page to add the mapping to
1078  * @vma:        the vm area in which the mapping is added
1079  * @address:    the user virtual address mapped
1080  * @compound:   charge the page as compound or small page
1081  *
1082  * The caller needs to hold the pte lock, and the page must be locked in
1083  * the anon_vma case: to serialize mapping,index checking after setting,
1084  * and to ensure that PageAnon is not being upgraded racily to PageKsm
1085  * (but PageKsm is never downgraded to PageAnon).
1086  */
1087 void page_add_anon_rmap(struct page *page,
1088         struct vm_area_struct *vma, unsigned long address, bool compound)
1089 {
1090         do_page_add_anon_rmap(page, vma, address, compound ? RMAP_COMPOUND : 0);
1091 }
1092 
1093 /*
1094  * Special version of the above for do_swap_page, which often runs
1095  * into pages that are exclusively owned by the current process.
1096  * Everybody else should continue to use page_add_anon_rmap above.
1097  */
1098 void do_page_add_anon_rmap(struct page *page,
1099         struct vm_area_struct *vma, unsigned long address, int flags)
1100 {
1101         bool compound = flags & RMAP_COMPOUND;
1102         bool first;
1103 
1104         if (compound) {
1105                 atomic_t *mapcount;
1106                 VM_BUG_ON_PAGE(!PageLocked(page), page);
1107                 VM_BUG_ON_PAGE(!PageTransHuge(page), page);
1108                 mapcount = compound_mapcount_ptr(page);
1109                 first = atomic_inc_and_test(mapcount);
1110         } else {
1111                 first = atomic_inc_and_test(&page->_mapcount);
1112         }
1113 
1114         if (first) {
1115                 int nr = compound ? hpage_nr_pages(page) : 1;
1116                 /*
1117                  * We use the irq-unsafe __{inc|mod}_zone_page_stat because
1118                  * these counters are not modified in interrupt context, and
1119                  * pte lock(a spinlock) is held, which implies preemption
1120                  * disabled.
1121                  */
1122                 if (compound)
1123                         __inc_node_page_state(page, NR_ANON_THPS);
1124                 __mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, nr);
1125         }
1126         if (unlikely(PageKsm(page)))
1127                 return;
1128 
1129         VM_BUG_ON_PAGE(!PageLocked(page), page);
1130 
1131         /* address might be in next vma when migration races vma_adjust */
1132         if (first)
1133                 __page_set_anon_rmap(page, vma, address,
1134                                 flags & RMAP_EXCLUSIVE);
1135         else
1136                 __page_check_anon_rmap(page, vma, address);
1137 }
1138 
1139 /**
1140  * page_add_new_anon_rmap - add pte mapping to a new anonymous page
1141  * @page:       the page to add the mapping to
1142  * @vma:        the vm area in which the mapping is added
1143  * @address:    the user virtual address mapped
1144  * @compound:   charge the page as compound or small page
1145  *
1146  * Same as page_add_anon_rmap but must only be called on *new* pages.
1147  * This means the inc-and-test can be bypassed.
1148  * Page does not have to be locked.
1149  */
1150 void page_add_new_anon_rmap(struct page *page,
1151         struct vm_area_struct *vma, unsigned long address, bool compound)
1152 {
1153         int nr = compound ? hpage_nr_pages(page) : 1;
1154 
1155         VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
1156         __SetPageSwapBacked(page);
1157         if (compound) {
1158                 VM_BUG_ON_PAGE(!PageTransHuge(page), page);
1159                 /* increment count (starts at -1) */
1160                 atomic_set(compound_mapcount_ptr(page), 0);
1161                 __inc_node_page_state(page, NR_ANON_THPS);
1162         } else {
1163                 /* Anon THP always mapped first with PMD */
1164                 VM_BUG_ON_PAGE(PageTransCompound(page), page);
1165                 /* increment count (starts at -1) */
1166                 atomic_set(&page->_mapcount, 0);
1167         }
1168         __mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, nr);
1169         __page_set_anon_rmap(page, vma, address, 1);
1170 }
1171 
1172 /**
1173  * page_add_file_rmap - add pte mapping to a file page
1174  * @page: the page to add the mapping to
1175  * @compound: charge the page as compound or small page
1176  *
1177  * The caller needs to hold the pte lock.
1178  */
1179 void page_add_file_rmap(struct page *page, bool compound)
1180 {
1181         int i, nr = 1;
1182 
1183         VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
1184         lock_page_memcg(page);
1185         if (compound && PageTransHuge(page)) {
1186                 for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
1187                         if (atomic_inc_and_test(&page[i]._mapcount))
1188                                 nr++;
1189                 }
1190                 if (!atomic_inc_and_test(compound_mapcount_ptr(page)))
1191                         goto out;
1192                 VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
1193                 __inc_node_page_state(page, NR_SHMEM_PMDMAPPED);
1194         } else {
1195                 if (PageTransCompound(page) && page_mapping(page)) {
1196                         VM_WARN_ON_ONCE(!PageLocked(page));
1197 
1198                         SetPageDoubleMap(compound_head(page));
1199                         if (PageMlocked(page))
1200                                 clear_page_mlock(compound_head(page));
1201                 }
1202                 if (!atomic_inc_and_test(&page->_mapcount))
1203                         goto out;
1204         }
1205         __mod_lruvec_page_state(page, NR_FILE_MAPPED, nr);
1206 out:
1207         unlock_page_memcg(page);
1208 }
1209 
1210 static void page_remove_file_rmap(struct page *page, bool compound)
1211 {
1212         int i, nr = 1;
1213 
1214         VM_BUG_ON_PAGE(compound && !PageHead(page), page);
1215         lock_page_memcg(page);
1216 
1217         /* Hugepages are not counted in NR_FILE_MAPPED for now. */
1218         if (unlikely(PageHuge(page))) {
1219                 /* hugetlb pages are always mapped with pmds */
1220                 atomic_dec(compound_mapcount_ptr(page));
1221                 goto out;
1222         }
1223 
1224         /* page still mapped by someone else? */
1225         if (compound && PageTransHuge(page)) {
1226                 for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
1227                         if (atomic_add_negative(-1, &page[i]._mapcount))
1228                                 nr++;
1229                 }
1230                 if (!atomic_add_negative(-1, compound_mapcount_ptr(page)))
1231                         goto out;
1232                 VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
1233                 __dec_node_page_state(page, NR_SHMEM_PMDMAPPED);
1234         } else {
1235                 if (!atomic_add_negative(-1, &page->_mapcount))
1236                         goto out;
1237         }
1238 
1239         /*
1240          * We use the irq-unsafe __{inc|mod}_lruvec_page_state because
1241          * these counters are not modified in interrupt context, and
1242          * pte lock(a spinlock) is held, which implies preemption disabled.
1243          */
1244         __mod_lruvec_page_state(page, NR_FILE_MAPPED, -nr);
1245 
1246         if (unlikely(PageMlocked(page)))
1247                 clear_page_mlock(page);
1248 out:
1249         unlock_page_memcg(page);
1250 }
1251 
1252 static void page_remove_anon_compound_rmap(struct page *page)
1253 {
1254         int i, nr;
1255 
1256         if (!atomic_add_negative(-1, compound_mapcount_ptr(page)))
1257                 return;
1258 
1259         /* Hugepages are not counted in NR_ANON_PAGES for now. */
1260         if (unlikely(PageHuge(page)))
1261                 return;
1262 
1263         if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
1264                 return;
1265 
1266         __dec_node_page_state(page, NR_ANON_THPS);
1267 
1268         if (TestClearPageDoubleMap(page)) {
1269                 /*
1270                  * Subpages can be mapped with PTEs too. Check how many of
1271                  * themi are still mapped.
1272                  */
1273                 for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
1274                         if (atomic_add_negative(-1, &page[i]._mapcount))
1275                                 nr++;
1276                 }
1277         } else {
1278                 nr = HPAGE_PMD_NR;
1279         }
1280 
1281         if (unlikely(PageMlocked(page)))
1282                 clear_page_mlock(page);
1283 
1284         if (nr) {
1285                 __mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr);
1286                 deferred_split_huge_page(page);
1287         }
1288 }
1289 
1290 /**
1291  * page_remove_rmap - take down pte mapping from a page
1292  * @page:       page to remove mapping from
1293  * @compound:   uncharge the page as compound or small page
1294  *
1295  * The caller needs to hold the pte lock.
1296  */
1297 void page_remove_rmap(struct page *page, bool compound)
1298 {
1299         if (!PageAnon(page))
1300                 return page_remove_file_rmap(page, compound);
1301 
1302         if (compound)
1303                 return page_remove_anon_compound_rmap(page);
1304 
1305         /* page still mapped by someone else? */
1306         if (!atomic_add_negative(-1, &page->_mapcount))
1307                 return;
1308 
1309         /*
1310          * We use the irq-unsafe __{inc|mod}_zone_page_stat because
1311          * these counters are not modified in interrupt context, and
1312          * pte lock(a spinlock) is held, which implies preemption disabled.
1313          */
1314         __dec_node_page_state(page, NR_ANON_MAPPED);
1315 
1316         if (unlikely(PageMlocked(page)))
1317                 clear_page_mlock(page);
1318 
1319         if (PageTransCompound(page))
1320                 deferred_split_huge_page(compound_head(page));
1321 
1322         /*
1323          * It would be tidy to reset the PageAnon mapping here,
1324          * but that might overwrite a racing page_add_anon_rmap
1325          * which increments mapcount after us but sets mapping
1326          * before us: so leave the reset to free_unref_page,
1327          * and remember that it's only reliable while mapped.
1328          * Leaving it set also helps swapoff to reinstate ptes
1329          * faster for those pages still in swapcache.
1330          */
1331 }
1332 
1333 /*
1334  * @arg: enum ttu_flags will be passed to this argument
1335  */
1336 static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
1337                      unsigned long address, void *arg)
1338 {
1339         struct mm_struct *mm = vma->vm_mm;
1340         struct page_vma_mapped_walk pvmw = {
1341                 .page = page,
1342                 .vma = vma,
1343                 .address = address,
1344         };
1345         pte_t pteval;
1346         struct page *subpage;
1347         bool ret = true;
1348         unsigned long start = address, end;
1349         enum ttu_flags flags = (enum ttu_flags)arg;
1350 
1351         /* munlock has nothing to gain from examining un-locked vmas */
1352         if ((flags & TTU_MUNLOCK) && !(vma->vm_flags & VM_LOCKED))
1353                 return true;
1354 
1355         if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) &&
1356             is_zone_device_page(page) && !is_device_private_page(page))
1357                 return true;
1358 
1359         if (flags & TTU_SPLIT_HUGE_PMD) {
1360                 split_huge_pmd_address(vma, address,
1361                                 flags & TTU_SPLIT_FREEZE, page);
1362         }
1363 
1364         /*
1365          * For THP, we have to assume the worse case ie pmd for invalidation.
1366          * For hugetlb, it could be much worse if we need to do pud
1367          * invalidation in the case of pmd sharing.
1368          *
1369          * Note that the page can not be free in this function as call of
1370          * try_to_unmap() must hold a reference on the page.
1371          */
1372         end = min(vma->vm_end, start + (PAGE_SIZE << compound_order(page)));
1373         if (PageHuge(page)) {
1374                 /*
1375                  * If sharing is possible, start and end will be adjusted
1376                  * accordingly.
1377                  */
1378                 adjust_range_if_pmd_sharing_possible(vma, &start, &end);
1379         }
1380         mmu_notifier_invalidate_range_start(vma->vm_mm, start, end);
1381 
1382         while (page_vma_mapped_walk(&pvmw)) {
1383 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
1384                 /* PMD-mapped THP migration entry */
1385                 if (!pvmw.pte && (flags & TTU_MIGRATION)) {
1386                         VM_BUG_ON_PAGE(PageHuge(page) || !PageTransCompound(page), page);
1387 
1388                         set_pmd_migration_entry(&pvmw, page);
1389                         continue;
1390                 }
1391 #endif
1392 
1393                 /*
1394                  * If the page is mlock()d, we cannot swap it out.
1395                  * If it's recently referenced (perhaps page_referenced
1396                  * skipped over this mm) then we should reactivate it.
1397                  */
1398                 if (!(flags & TTU_IGNORE_MLOCK)) {
1399                         if (vma->vm_flags & VM_LOCKED) {
1400                                 /* PTE-mapped THP are never mlocked */
1401                                 if (!PageTransCompound(page)) {
1402                                         /*
1403                                          * Holding pte lock, we do *not* need
1404                                          * mmap_sem here
1405                                          */
1406                                         mlock_vma_page(page);
1407                                 }
1408                                 ret = false;
1409                                 page_vma_mapped_walk_done(&pvmw);
1410                                 break;
1411                         }
1412                         if (flags & TTU_MUNLOCK)
1413                                 continue;
1414                 }
1415 
1416                 /* Unexpected PMD-mapped THP? */
1417                 VM_BUG_ON_PAGE(!pvmw.pte, page);
1418 
1419                 subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte);
1420                 address = pvmw.address;
1421 
1422                 if (PageHuge(page)) {
1423                         if (huge_pmd_unshare(mm, &address, pvmw.pte)) {
1424                                 /*
1425                                  * huge_pmd_unshare unmapped an entire PMD
1426                                  * page.  There is no way of knowing exactly
1427                                  * which PMDs may be cached for this mm, so
1428                                  * we must flush them all.  start/end were
1429                                  * already adjusted above to cover this range.
1430                                  */
1431                                 flush_cache_range(vma, start, end);
1432                                 flush_tlb_range(vma, start, end);
1433                                 mmu_notifier_invalidate_range(mm, start, end);
1434 
1435                                 /*
1436                                  * The ref count of the PMD page was dropped
1437                                  * which is part of the way map counting
1438                                  * is done for shared PMDs.  Return 'true'
1439                                  * here.  When there is no other sharing,
1440                                  * huge_pmd_unshare returns false and we will
1441                                  * unmap the actual page and drop map count
1442                                  * to zero.
1443                                  */
1444                                 page_vma_mapped_walk_done(&pvmw);
1445                                 break;
1446                         }
1447                 }
1448 
1449                 if (IS_ENABLED(CONFIG_MIGRATION) &&
1450                     (flags & TTU_MIGRATION) &&
1451                     is_zone_device_page(page)) {
1452                         swp_entry_t entry;
1453                         pte_t swp_pte;
1454 
1455                         pteval = ptep_get_and_clear(mm, pvmw.address, pvmw.pte);
1456 
1457                         /*
1458                          * Store the pfn of the page in a special migration
1459                          * pte. do_swap_page() will wait until the migration
1460                          * pte is removed and then restart fault handling.
1461                          */
1462                         entry = make_migration_entry(page, 0);
1463                         swp_pte = swp_entry_to_pte(entry);
1464                         if (pte_soft_dirty(pteval))
1465                                 swp_pte = pte_swp_mksoft_dirty(swp_pte);
1466                         set_pte_at(mm, pvmw.address, pvmw.pte, swp_pte);
1467                         /*
1468                          * No need to invalidate here it will synchronize on
1469                          * against the special swap migration pte.
1470                          */
1471                         goto discard;
1472                 }
1473 
1474                 if (!(flags & TTU_IGNORE_ACCESS)) {
1475                         if (ptep_clear_flush_young_notify(vma, address,
1476                                                 pvmw.pte)) {
1477                                 ret = false;
1478                                 page_vma_mapped_walk_done(&pvmw);
1479                                 break;
1480                         }
1481                 }
1482 
1483                 /* Nuke the page table entry. */
1484                 flush_cache_page(vma, address, pte_pfn(*pvmw.pte));
1485                 if (should_defer_flush(mm, flags)) {
1486                         /*
1487                          * We clear the PTE but do not flush so potentially
1488                          * a remote CPU could still be writing to the page.
1489                          * If the entry was previously clean then the
1490                          * architecture must guarantee that a clear->dirty
1491                          * transition on a cached TLB entry is written through
1492                          * and traps if the PTE is unmapped.
1493                          */
1494                         pteval = ptep_get_and_clear(mm, address, pvmw.pte);
1495 
1496                         set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
1497                 } else {
1498                         pteval = ptep_clear_flush(vma, address, pvmw.pte);
1499                 }
1500 
1501                 /* Move the dirty bit to the page. Now the pte is gone. */
1502                 if (pte_dirty(pteval))
1503                         set_page_dirty(page);
1504 
1505                 /* Update high watermark before we lower rss */
1506                 update_hiwater_rss(mm);
1507 
1508                 if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {
1509                         pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
1510                         if (PageHuge(page)) {
1511                                 int nr = 1 << compound_order(page);
1512                                 hugetlb_count_sub(nr, mm);
1513                                 set_huge_swap_pte_at(mm, address,
1514                                                      pvmw.pte, pteval,
1515                                                      vma_mmu_pagesize(vma));
1516                         } else {
1517                                 dec_mm_counter(mm, mm_counter(page));
1518                                 set_pte_at(mm, address, pvmw.pte, pteval);
1519                         }
1520 
1521                 } else if (pte_unused(pteval) && !userfaultfd_armed(vma)) {
1522                         /*
1523                          * The guest indicated that the page content is of no
1524                          * interest anymore. Simply discard the pte, vmscan
1525                          * will take care of the rest.
1526                          * A future reference will then fault in a new zero
1527                          * page. When userfaultfd is active, we must not drop
1528                          * this page though, as its main user (postcopy
1529                          * migration) will not expect userfaults on already
1530                          * copied pages.
1531                          */
1532                         dec_mm_counter(mm, mm_counter(page));
1533                         /* We have to invalidate as we cleared the pte */
1534                         mmu_notifier_invalidate_range(mm, address,
1535                                                       address + PAGE_SIZE);
1536                 } else if (IS_ENABLED(CONFIG_MIGRATION) &&
1537                                 (flags & (TTU_MIGRATION|TTU_SPLIT_FREEZE))) {
1538                         swp_entry_t entry;
1539                         pte_t swp_pte;
1540 
1541                         if (arch_unmap_one(mm, vma, address, pteval) < 0) {
1542                                 set_pte_at(mm, address, pvmw.pte, pteval);
1543                                 ret = false;
1544                                 page_vma_mapped_walk_done(&pvmw);
1545                                 break;
1546                         }
1547 
1548                         /*
1549                          * Store the pfn of the page in a special migration
1550                          * pte. do_swap_page() will wait until the migration
1551                          * pte is removed and then restart fault handling.
1552                          */
1553                         entry = make_migration_entry(subpage,
1554                                         pte_write(pteval));
1555                         swp_pte = swp_entry_to_pte(entry);
1556                         if (pte_soft_dirty(pteval))
1557                                 swp_pte = pte_swp_mksoft_dirty(swp_pte);
1558                         set_pte_at(mm, address, pvmw.pte, swp_pte);
1559                         /*
1560                          * No need to invalidate here it will synchronize on
1561                          * against the special swap migration pte.
1562                          */
1563                 } else if (PageAnon(page)) {
1564                         swp_entry_t entry = { .val = page_private(subpage) };
1565                         pte_t swp_pte;
1566                         /*
1567                          * Store the swap location in the pte.
1568                          * See handle_pte_fault() ...
1569                          */
1570                         if (unlikely(PageSwapBacked(page) != PageSwapCache(page))) {
1571                                 WARN_ON_ONCE(1);
1572                                 ret = false;
1573                                 /* We have to invalidate as we cleared the pte */
1574                                 mmu_notifier_invalidate_range(mm, address,
1575                                                         address + PAGE_SIZE);
1576                                 page_vma_mapped_walk_done(&pvmw);
1577                                 break;
1578                         }
1579 
1580                         /* MADV_FREE page check */
1581                         if (!PageSwapBacked(page)) {
1582                                 if (!PageDirty(page)) {
1583                                         /* Invalidate as we cleared the pte */
1584                                         mmu_notifier_invalidate_range(mm,
1585                                                 address, address + PAGE_SIZE);
1586                                         dec_mm_counter(mm, MM_ANONPAGES);
1587                                         goto discard;
1588                                 }
1589 
1590                                 /*
1591                                  * If the page was redirtied, it cannot be
1592                                  * discarded. Remap the page to page table.
1593                                  */
1594                                 set_pte_at(mm, address, pvmw.pte, pteval);
1595                                 SetPageSwapBacked(page);
1596                                 ret = false;
1597                                 page_vma_mapped_walk_done(&pvmw);
1598                                 break;
1599                         }
1600 
1601                         if (swap_duplicate(entry) < 0) {
1602                                 set_pte_at(mm, address, pvmw.pte, pteval);
1603                                 ret = false;
1604                                 page_vma_mapped_walk_done(&pvmw);
1605                                 break;
1606                         }
1607                         if (arch_unmap_one(mm, vma, address, pteval) < 0) {
1608                                 set_pte_at(mm, address, pvmw.pte, pteval);
1609                                 ret = false;
1610                                 page_vma_mapped_walk_done(&pvmw);
1611                                 break;
1612                         }
1613                         if (list_empty(&mm->mmlist)) {
1614                                 spin_lock(&mmlist_lock);
1615                                 if (list_empty(&mm->mmlist))
1616                                         list_add(&mm->mmlist, &init_mm.mmlist);
1617                                 spin_unlock(&mmlist_lock);
1618                         }
1619                         dec_mm_counter(mm, MM_ANONPAGES);
1620                         inc_mm_counter(mm, MM_SWAPENTS);
1621                         swp_pte = swp_entry_to_pte(entry);
1622                         if (pte_soft_dirty(pteval))
1623                                 swp_pte = pte_swp_mksoft_dirty(swp_pte);
1624                         set_pte_at(mm, address, pvmw.pte, swp_pte);
1625                         /* Invalidate as we cleared the pte */
1626                         mmu_notifier_invalidate_range(mm, address,
1627                                                       address + PAGE_SIZE);
1628                 } else {
1629                         /*
1630                          * We should not need to notify here as we reach this
1631                          * case only from freeze_page() itself only call from
1632                          * split_huge_page_to_list() so everything below must
1633                          * be true:
1634                          *   - page is not anonymous
1635                          *   - page is locked
1636                          *
1637                          * So as it is a locked file back page thus it can not
1638                          * be remove from the page cache and replace by a new
1639                          * page before mmu_notifier_invalidate_range_end so no
1640                          * concurrent thread might update its page table to
1641                          * point at new page while a device still is using this
1642                          * page.
1643                          *
1644                          * See Documentation/vm/mmu_notifier.rst
1645                          */
1646                         dec_mm_counter(mm, mm_counter_file(page));
1647                 }
1648 discard:
1649                 /*
1650                  * No need to call mmu_notifier_invalidate_range() it has be
1651                  * done above for all cases requiring it to happen under page
1652                  * table lock before mmu_notifier_invalidate_range_end()
1653                  *
1654                  * See Documentation/vm/mmu_notifier.rst
1655                  */
1656                 page_remove_rmap(subpage, PageHuge(page));
1657                 put_page(page);
1658         }
1659 
1660         mmu_notifier_invalidate_range_end(vma->vm_mm, start, end);
1661 
1662         return ret;
1663 }
1664 
1665 bool is_vma_temporary_stack(struct vm_area_struct *vma)
1666 {
1667         int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);
1668 
1669         if (!maybe_stack)
1670                 return false;
1671 
1672         if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
1673                                                 VM_STACK_INCOMPLETE_SETUP)
1674                 return true;
1675 
1676         return false;
1677 }
1678 
1679 static bool invalid_migration_vma(struct vm_area_struct *vma, void *arg)
1680 {
1681         return is_vma_temporary_stack(vma);
1682 }
1683 
1684 static int page_mapcount_is_zero(struct page *page)
1685 {
1686         return !total_mapcount(page);
1687 }
1688 
1689 /**
1690  * try_to_unmap - try to remove all page table mappings to a page
1691  * @page: the page to get unmapped
1692  * @flags: action and flags
1693  *
1694  * Tries to remove all the page table entries which are mapping this
1695  * page, used in the pageout path.  Caller must hold the page lock.
1696  *
1697  * If unmap is successful, return true. Otherwise, false.
1698  */
1699 bool try_to_unmap(struct page *page, enum ttu_flags flags)
1700 {
1701         struct rmap_walk_control rwc = {
1702                 .rmap_one = try_to_unmap_one,
1703                 .arg = (void *)flags,
1704                 .done = page_mapcount_is_zero,
1705                 .anon_lock = page_lock_anon_vma_read,
1706         };
1707 
1708         /*
1709          * During exec, a temporary VMA is setup and later moved.
1710          * The VMA is moved under the anon_vma lock but not the
1711          * page tables leading to a race where migration cannot
1712          * find the migration ptes. Rather than increasing the
1713          * locking requirements of exec(), migration skips
1714          * temporary VMAs until after exec() completes.
1715          */
1716         if ((flags & (TTU_MIGRATION|TTU_SPLIT_FREEZE))
1717             && !PageKsm(page) && PageAnon(page))
1718                 rwc.invalid_vma = invalid_migration_vma;
1719 
1720         if (flags & TTU_RMAP_LOCKED)
1721                 rmap_walk_locked(page, &rwc);
1722         else
1723                 rmap_walk(page, &rwc);
1724 
1725         return !page_mapcount(page) ? true : false;
1726 }
1727 
1728 static int page_not_mapped(struct page *page)
1729 {
1730         return !page_mapped(page);
1731 };
1732 
1733 /**
1734  * try_to_munlock - try to munlock a page
1735  * @page: the page to be munlocked
1736  *
1737  * Called from munlock code.  Checks all of the VMAs mapping the page
1738  * to make sure nobody else has this page mlocked. The page will be
1739  * returned with PG_mlocked cleared if no other vmas have it mlocked.
1740  */
1741 
1742 void try_to_munlock(struct page *page)
1743 {
1744         struct rmap_walk_control rwc = {
1745                 .rmap_one = try_to_unmap_one,
1746                 .arg = (void *)TTU_MUNLOCK,
1747                 .done = page_not_mapped,
1748                 .anon_lock = page_lock_anon_vma_read,
1749 
1750         };
1751 
1752         VM_BUG_ON_PAGE(!PageLocked(page) || PageLRU(page), page);
1753         VM_BUG_ON_PAGE(PageCompound(page) && PageDoubleMap(page), page);
1754 
1755         rmap_walk(page, &rwc);
1756 }
1757 
1758 void __put_anon_vma(struct anon_vma *anon_vma)
1759 {
1760         struct anon_vma *root = anon_vma->root;
1761 
1762         anon_vma_free(anon_vma);
1763         if (root != anon_vma && atomic_dec_and_test(&root->refcount))
1764                 anon_vma_free(root);
1765 }
1766 
1767 static struct anon_vma *rmap_walk_anon_lock(struct page *page,
1768                                         struct rmap_walk_control *rwc)
1769 {
1770         struct anon_vma *anon_vma;
1771 
1772         if (rwc->anon_lock)
1773                 return rwc->anon_lock(page);
1774 
1775         /*
1776          * Note: remove_migration_ptes() cannot use page_lock_anon_vma_read()
1777          * because that depends on page_mapped(); but not all its usages
1778          * are holding mmap_sem. Users without mmap_sem are required to
1779          * take a reference count to prevent the anon_vma disappearing
1780          */
1781         anon_vma = page_anon_vma(page);
1782         if (!anon_vma)
1783                 return NULL;
1784 
1785         anon_vma_lock_read(anon_vma);
1786         return anon_vma;
1787 }
1788 
1789 /*
1790  * rmap_walk_anon - do something to anonymous page using the object-based
1791  * rmap method
1792  * @page: the page to be handled
1793  * @rwc: control variable according to each walk type
1794  *
1795  * Find all the mappings of a page using the mapping pointer and the vma chains
1796  * contained in the anon_vma struct it points to.
1797  *
1798  * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
1799  * where the page was found will be held for write.  So, we won't recheck
1800  * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
1801  * LOCKED.
1802  */
1803 static void rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc,
1804                 bool locked)
1805 {
1806         struct anon_vma *anon_vma;
1807         pgoff_t pgoff_start, pgoff_end;
1808         struct anon_vma_chain *avc;
1809 
1810         if (locked) {
1811                 anon_vma = page_anon_vma(page);
1812                 /* anon_vma disappear under us? */
1813                 VM_BUG_ON_PAGE(!anon_vma, page);
1814         } else {
1815                 anon_vma = rmap_walk_anon_lock(page, rwc);
1816         }
1817         if (!anon_vma)
1818                 return;
1819 
1820         pgoff_start = page_to_pgoff(page);
1821         pgoff_end = pgoff_start + hpage_nr_pages(page) - 1;
1822         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root,
1823                         pgoff_start, pgoff_end) {
1824                 struct vm_area_struct *vma = avc->vma;
1825                 unsigned long address = vma_address(page, vma);
1826 
1827                 cond_resched();
1828 
1829                 if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
1830                         continue;
1831 
1832                 if (!rwc->rmap_one(page, vma, address, rwc->arg))
1833                         break;
1834                 if (rwc->done && rwc->done(page))
1835                         break;
1836         }
1837 
1838         if (!locked)
1839                 anon_vma_unlock_read(anon_vma);
1840 }
1841 
1842 /*
1843  * rmap_walk_file - do something to file page using the object-based rmap method
1844  * @page: the page to be handled
1845  * @rwc: control variable according to each walk type
1846  *
1847  * Find all the mappings of a page using the mapping pointer and the vma chains
1848  * contained in the address_space struct it points to.
1849  *
1850  * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
1851  * where the page was found will be held for write.  So, we won't recheck
1852  * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
1853  * LOCKED.
1854  */
1855 static void rmap_walk_file(struct page *page, struct rmap_walk_control *rwc,
1856                 bool locked)
1857 {
1858         struct address_space *mapping = page_mapping(page);
1859         pgoff_t pgoff_start, pgoff_end;
1860         struct vm_area_struct *vma;
1861 
1862         /*
1863          * The page lock not only makes sure that page->mapping cannot
1864          * suddenly be NULLified by truncation, it makes sure that the
1865          * structure at mapping cannot be freed and reused yet,
1866          * so we can safely take mapping->i_mmap_rwsem.
1867          */
1868         VM_BUG_ON_PAGE(!PageLocked(page), page);
1869 
1870         if (!mapping)
1871                 return;
1872 
1873         pgoff_start = page_to_pgoff(page);
1874         pgoff_end = pgoff_start + hpage_nr_pages(page) - 1;
1875         if (!locked)
1876                 i_mmap_lock_read(mapping);
1877         vma_interval_tree_foreach(vma, &mapping->i_mmap,
1878                         pgoff_start, pgoff_end) {
1879                 unsigned long address = vma_address(page, vma);
1880 
1881                 cond_resched();
1882 
1883                 if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
1884                         continue;
1885 
1886                 if (!rwc->rmap_one(page, vma, address, rwc->arg))
1887                         goto done;
1888                 if (rwc->done && rwc->done(page))
1889                         goto done;
1890         }
1891 
1892 done:
1893         if (!locked)
1894                 i_mmap_unlock_read(mapping);
1895 }
1896 
1897 void rmap_walk(struct page *page, struct rmap_walk_control *rwc)
1898 {
1899         if (unlikely(PageKsm(page)))
1900                 rmap_walk_ksm(page, rwc);
1901         else if (PageAnon(page))
1902                 rmap_walk_anon(page, rwc, false);
1903         else
1904                 rmap_walk_file(page, rwc, false);
1905 }
1906 
1907 /* Like rmap_walk, but caller holds relevant rmap lock */
1908 void rmap_walk_locked(struct page *page, struct rmap_walk_control *rwc)
1909 {
1910         /* no ksm support for now */
1911         VM_BUG_ON_PAGE(PageKsm(page), page);
1912         if (PageAnon(page))
1913                 rmap_walk_anon(page, rwc, true);
1914         else
1915                 rmap_walk_file(page, rwc, true);
1916 }
1917 
1918 #ifdef CONFIG_HUGETLB_PAGE
1919 /*
1920  * The following three functions are for anonymous (private mapped) hugepages.
1921  * Unlike common anonymous pages, anonymous hugepages have no accounting code
1922  * and no lru code, because we handle hugepages differently from common pages.
1923  */
1924 static void __hugepage_set_anon_rmap(struct page *page,
1925         struct vm_area_struct *vma, unsigned long address, int exclusive)
1926 {
1927         struct anon_vma *anon_vma = vma->anon_vma;
1928 
1929         BUG_ON(!anon_vma);
1930 
1931         if (PageAnon(page))
1932                 return;
1933         if (!exclusive)
1934                 anon_vma = anon_vma->root;
1935 
1936         anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1937         page->mapping = (struct address_space *) anon_vma;
1938         page->index = linear_page_index(vma, address);
1939 }
1940 
1941 void hugepage_add_anon_rmap(struct page *page,
1942                             struct vm_area_struct *vma, unsigned long address)
1943 {
1944         struct anon_vma *anon_vma = vma->anon_vma;
1945         int first;
1946 
1947         BUG_ON(!PageLocked(page));
1948         BUG_ON(!anon_vma);
1949         /* address might be in next vma when migration races vma_adjust */
1950         first = atomic_inc_and_test(compound_mapcount_ptr(page));
1951         if (first)
1952                 __hugepage_set_anon_rmap(page, vma, address, 0);
1953 }
1954 
1955 void hugepage_add_new_anon_rmap(struct page *page,
1956                         struct vm_area_struct *vma, unsigned long address)
1957 {
1958         BUG_ON(address < vma->vm_start || address >= vma->vm_end);
1959         atomic_set(compound_mapcount_ptr(page), 0);
1960         __hugepage_set_anon_rmap(page, vma, address, 1);
1961 }
1962 #endif /* CONFIG_HUGETLB_PAGE */
1963 

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