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TOMOYO Linux Cross Reference
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  *       mapping->i_mmap_mutex
 27  *         anon_vma->rwsem
 28  *           mm->page_table_lock or pte_lock
 29  *             zone->lru_lock (in mark_page_accessed, isolate_lru_page)
 30  *             swap_lock (in swap_duplicate, swap_info_get)
 31  *               mmlist_lock (in mmput, drain_mmlist and others)
 32  *               mapping->private_lock (in __set_page_dirty_buffers)
 33  *               inode->i_lock (in set_page_dirty's __mark_inode_dirty)
 34  *               bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
 35  *                 sb_lock (within inode_lock in fs/fs-writeback.c)
 36  *                 mapping->tree_lock (widely used, in set_page_dirty,
 37  *                           in arch-dependent flush_dcache_mmap_lock,
 38  *                           within bdi.wb->list_lock in __sync_single_inode)
 39  *
 40  * anon_vma->rwsem,mapping->i_mutex      (memory_failure, collect_procs_anon)
 41  *   ->tasklist_lock
 42  *     pte map lock
 43  */
 44 
 45 #include <linux/mm.h>
 46 #include <linux/pagemap.h>
 47 #include <linux/swap.h>
 48 #include <linux/swapops.h>
 49 #include <linux/slab.h>
 50 #include <linux/init.h>
 51 #include <linux/ksm.h>
 52 #include <linux/rmap.h>
 53 #include <linux/rcupdate.h>
 54 #include <linux/export.h>
 55 #include <linux/memcontrol.h>
 56 #include <linux/mmu_notifier.h>
 57 #include <linux/migrate.h>
 58 #include <linux/hugetlb.h>
 59 #include <linux/backing-dev.h>
 60 
 61 #include <asm/tlbflush.h>
 62 
 63 #include "internal.h"
 64 
 65 static struct kmem_cache *anon_vma_cachep;
 66 static struct kmem_cache *anon_vma_chain_cachep;
 67 
 68 static inline struct anon_vma *anon_vma_alloc(void)
 69 {
 70         struct anon_vma *anon_vma;
 71 
 72         anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
 73         if (anon_vma) {
 74                 atomic_set(&anon_vma->refcount, 1);
 75                 /*
 76                  * Initialise the anon_vma root to point to itself. If called
 77                  * from fork, the root will be reset to the parents anon_vma.
 78                  */
 79                 anon_vma->root = anon_vma;
 80         }
 81 
 82         return anon_vma;
 83 }
 84 
 85 static inline void anon_vma_free(struct anon_vma *anon_vma)
 86 {
 87         VM_BUG_ON(atomic_read(&anon_vma->refcount));
 88 
 89         /*
 90          * Synchronize against page_lock_anon_vma_read() such that
 91          * we can safely hold the lock without the anon_vma getting
 92          * freed.
 93          *
 94          * Relies on the full mb implied by the atomic_dec_and_test() from
 95          * put_anon_vma() against the acquire barrier implied by
 96          * down_read_trylock() from page_lock_anon_vma_read(). This orders:
 97          *
 98          * page_lock_anon_vma_read()    VS      put_anon_vma()
 99          *   down_read_trylock()                  atomic_dec_and_test()
100          *   LOCK                                 MB
101          *   atomic_read()                        rwsem_is_locked()
102          *
103          * LOCK should suffice since the actual taking of the lock must
104          * happen _before_ what follows.
105          */
106         if (rwsem_is_locked(&anon_vma->root->rwsem)) {
107                 anon_vma_lock_write(anon_vma);
108                 anon_vma_unlock(anon_vma);
109         }
110 
111         kmem_cache_free(anon_vma_cachep, anon_vma);
112 }
113 
114 static inline struct anon_vma_chain *anon_vma_chain_alloc(gfp_t gfp)
115 {
116         return kmem_cache_alloc(anon_vma_chain_cachep, gfp);
117 }
118 
119 static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
120 {
121         kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain);
122 }
123 
124 static void anon_vma_chain_link(struct vm_area_struct *vma,
125                                 struct anon_vma_chain *avc,
126                                 struct anon_vma *anon_vma)
127 {
128         avc->vma = vma;
129         avc->anon_vma = anon_vma;
130         list_add(&avc->same_vma, &vma->anon_vma_chain);
131         anon_vma_interval_tree_insert(avc, &anon_vma->rb_root);
132 }
133 
134 /**
135  * anon_vma_prepare - attach an anon_vma to a memory region
136  * @vma: the memory region in question
137  *
138  * This makes sure the memory mapping described by 'vma' has
139  * an 'anon_vma' attached to it, so that we can associate the
140  * anonymous pages mapped into it with that anon_vma.
141  *
142  * The common case will be that we already have one, but if
143  * not we either need to find an adjacent mapping that we
144  * can re-use the anon_vma from (very common when the only
145  * reason for splitting a vma has been mprotect()), or we
146  * allocate a new one.
147  *
148  * Anon-vma allocations are very subtle, because we may have
149  * optimistically looked up an anon_vma in page_lock_anon_vma_read()
150  * and that may actually touch the spinlock even in the newly
151  * allocated vma (it depends on RCU to make sure that the
152  * anon_vma isn't actually destroyed).
153  *
154  * As a result, we need to do proper anon_vma locking even
155  * for the new allocation. At the same time, we do not want
156  * to do any locking for the common case of already having
157  * an anon_vma.
158  *
159  * This must be called with the mmap_sem held for reading.
160  */
161 int anon_vma_prepare(struct vm_area_struct *vma)
162 {
163         struct anon_vma *anon_vma = vma->anon_vma;
164         struct anon_vma_chain *avc;
165 
166         might_sleep();
167         if (unlikely(!anon_vma)) {
168                 struct mm_struct *mm = vma->vm_mm;
169                 struct anon_vma *allocated;
170 
171                 avc = anon_vma_chain_alloc(GFP_KERNEL);
172                 if (!avc)
173                         goto out_enomem;
174 
175                 anon_vma = find_mergeable_anon_vma(vma);
176                 allocated = NULL;
177                 if (!anon_vma) {
178                         anon_vma = anon_vma_alloc();
179                         if (unlikely(!anon_vma))
180                                 goto out_enomem_free_avc;
181                         allocated = anon_vma;
182                 }
183 
184                 anon_vma_lock_write(anon_vma);
185                 /* page_table_lock to protect against threads */
186                 spin_lock(&mm->page_table_lock);
187                 if (likely(!vma->anon_vma)) {
188                         vma->anon_vma = anon_vma;
189                         anon_vma_chain_link(vma, avc, anon_vma);
190                         allocated = NULL;
191                         avc = NULL;
192                 }
193                 spin_unlock(&mm->page_table_lock);
194                 anon_vma_unlock(anon_vma);
195 
196                 if (unlikely(allocated))
197                         put_anon_vma(allocated);
198                 if (unlikely(avc))
199                         anon_vma_chain_free(avc);
200         }
201         return 0;
202 
203  out_enomem_free_avc:
204         anon_vma_chain_free(avc);
205  out_enomem:
206         return -ENOMEM;
207 }
208 
209 /*
210  * This is a useful helper function for locking the anon_vma root as
211  * we traverse the vma->anon_vma_chain, looping over anon_vma's that
212  * have the same vma.
213  *
214  * Such anon_vma's should have the same root, so you'd expect to see
215  * just a single mutex_lock for the whole traversal.
216  */
217 static inline struct anon_vma *lock_anon_vma_root(struct anon_vma *root, struct anon_vma *anon_vma)
218 {
219         struct anon_vma *new_root = anon_vma->root;
220         if (new_root != root) {
221                 if (WARN_ON_ONCE(root))
222                         up_write(&root->rwsem);
223                 root = new_root;
224                 down_write(&root->rwsem);
225         }
226         return root;
227 }
228 
229 static inline void unlock_anon_vma_root(struct anon_vma *root)
230 {
231         if (root)
232                 up_write(&root->rwsem);
233 }
234 
235 /*
236  * Attach the anon_vmas from src to dst.
237  * Returns 0 on success, -ENOMEM on failure.
238  */
239 int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
240 {
241         struct anon_vma_chain *avc, *pavc;
242         struct anon_vma *root = NULL;
243 
244         list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
245                 struct anon_vma *anon_vma;
246 
247                 avc = anon_vma_chain_alloc(GFP_NOWAIT | __GFP_NOWARN);
248                 if (unlikely(!avc)) {
249                         unlock_anon_vma_root(root);
250                         root = NULL;
251                         avc = anon_vma_chain_alloc(GFP_KERNEL);
252                         if (!avc)
253                                 goto enomem_failure;
254                 }
255                 anon_vma = pavc->anon_vma;
256                 root = lock_anon_vma_root(root, anon_vma);
257                 anon_vma_chain_link(dst, avc, anon_vma);
258         }
259         unlock_anon_vma_root(root);
260         return 0;
261 
262  enomem_failure:
263         unlink_anon_vmas(dst);
264         return -ENOMEM;
265 }
266 
267 /*
268  * Attach vma to its own anon_vma, as well as to the anon_vmas that
269  * the corresponding VMA in the parent process is attached to.
270  * Returns 0 on success, non-zero on failure.
271  */
272 int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
273 {
274         struct anon_vma_chain *avc;
275         struct anon_vma *anon_vma;
276 
277         /* Don't bother if the parent process has no anon_vma here. */
278         if (!pvma->anon_vma)
279                 return 0;
280 
281         /*
282          * First, attach the new VMA to the parent VMA's anon_vmas,
283          * so rmap can find non-COWed pages in child processes.
284          */
285         if (anon_vma_clone(vma, pvma))
286                 return -ENOMEM;
287 
288         /* Then add our own anon_vma. */
289         anon_vma = anon_vma_alloc();
290         if (!anon_vma)
291                 goto out_error;
292         avc = anon_vma_chain_alloc(GFP_KERNEL);
293         if (!avc)
294                 goto out_error_free_anon_vma;
295 
296         /*
297          * The root anon_vma's spinlock is the lock actually used when we
298          * lock any of the anon_vmas in this anon_vma tree.
299          */
300         anon_vma->root = pvma->anon_vma->root;
301         /*
302          * With refcounts, an anon_vma can stay around longer than the
303          * process it belongs to. The root anon_vma needs to be pinned until
304          * this anon_vma is freed, because the lock lives in the root.
305          */
306         get_anon_vma(anon_vma->root);
307         /* Mark this anon_vma as the one where our new (COWed) pages go. */
308         vma->anon_vma = anon_vma;
309         anon_vma_lock_write(anon_vma);
310         anon_vma_chain_link(vma, avc, anon_vma);
311         anon_vma_unlock(anon_vma);
312 
313         return 0;
314 
315  out_error_free_anon_vma:
316         put_anon_vma(anon_vma);
317  out_error:
318         unlink_anon_vmas(vma);
319         return -ENOMEM;
320 }
321 
322 void unlink_anon_vmas(struct vm_area_struct *vma)
323 {
324         struct anon_vma_chain *avc, *next;
325         struct anon_vma *root = NULL;
326 
327         /*
328          * Unlink each anon_vma chained to the VMA.  This list is ordered
329          * from newest to oldest, ensuring the root anon_vma gets freed last.
330          */
331         list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
332                 struct anon_vma *anon_vma = avc->anon_vma;
333 
334                 root = lock_anon_vma_root(root, anon_vma);
335                 anon_vma_interval_tree_remove(avc, &anon_vma->rb_root);
336 
337                 /*
338                  * Leave empty anon_vmas on the list - we'll need
339                  * to free them outside the lock.
340                  */
341                 if (RB_EMPTY_ROOT(&anon_vma->rb_root))
342                         continue;
343 
344                 list_del(&avc->same_vma);
345                 anon_vma_chain_free(avc);
346         }
347         unlock_anon_vma_root(root);
348 
349         /*
350          * Iterate the list once more, it now only contains empty and unlinked
351          * anon_vmas, destroy them. Could not do before due to __put_anon_vma()
352          * needing to write-acquire the anon_vma->root->rwsem.
353          */
354         list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
355                 struct anon_vma *anon_vma = avc->anon_vma;
356 
357                 put_anon_vma(anon_vma);
358 
359                 list_del(&avc->same_vma);
360                 anon_vma_chain_free(avc);
361         }
362 }
363 
364 static void anon_vma_ctor(void *data)
365 {
366         struct anon_vma *anon_vma = data;
367 
368         init_rwsem(&anon_vma->rwsem);
369         atomic_set(&anon_vma->refcount, 0);
370         anon_vma->rb_root = RB_ROOT;
371 }
372 
373 void __init anon_vma_init(void)
374 {
375         anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
376                         0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor);
377         anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC);
378 }
379 
380 /*
381  * Getting a lock on a stable anon_vma from a page off the LRU is tricky!
382  *
383  * Since there is no serialization what so ever against page_remove_rmap()
384  * the best this function can do is return a locked anon_vma that might
385  * have been relevant to this page.
386  *
387  * The page might have been remapped to a different anon_vma or the anon_vma
388  * returned may already be freed (and even reused).
389  *
390  * In case it was remapped to a different anon_vma, the new anon_vma will be a
391  * child of the old anon_vma, and the anon_vma lifetime rules will therefore
392  * ensure that any anon_vma obtained from the page will still be valid for as
393  * long as we observe page_mapped() [ hence all those page_mapped() tests ].
394  *
395  * All users of this function must be very careful when walking the anon_vma
396  * chain and verify that the page in question is indeed mapped in it
397  * [ something equivalent to page_mapped_in_vma() ].
398  *
399  * Since anon_vma's slab is DESTROY_BY_RCU and we know from page_remove_rmap()
400  * that the anon_vma pointer from page->mapping is valid if there is a
401  * mapcount, we can dereference the anon_vma after observing those.
402  */
403 struct anon_vma *page_get_anon_vma(struct page *page)
404 {
405         struct anon_vma *anon_vma = NULL;
406         unsigned long anon_mapping;
407 
408         rcu_read_lock();
409         anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
410         if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
411                 goto out;
412         if (!page_mapped(page))
413                 goto out;
414 
415         anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
416         if (!atomic_inc_not_zero(&anon_vma->refcount)) {
417                 anon_vma = NULL;
418                 goto out;
419         }
420 
421         /*
422          * If this page is still mapped, then its anon_vma cannot have been
423          * freed.  But if it has been unmapped, we have no security against the
424          * anon_vma structure being freed and reused (for another anon_vma:
425          * SLAB_DESTROY_BY_RCU guarantees that - so the atomic_inc_not_zero()
426          * above cannot corrupt).
427          */
428         if (!page_mapped(page)) {
429                 put_anon_vma(anon_vma);
430                 anon_vma = NULL;
431         }
432 out:
433         rcu_read_unlock();
434 
435         return anon_vma;
436 }
437 
438 /*
439  * Similar to page_get_anon_vma() except it locks the anon_vma.
440  *
441  * Its a little more complex as it tries to keep the fast path to a single
442  * atomic op -- the trylock. If we fail the trylock, we fall back to getting a
443  * reference like with page_get_anon_vma() and then block on the mutex.
444  */
445 struct anon_vma *page_lock_anon_vma_read(struct page *page)
446 {
447         struct anon_vma *anon_vma = NULL;
448         struct anon_vma *root_anon_vma;
449         unsigned long anon_mapping;
450 
451         rcu_read_lock();
452         anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
453         if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
454                 goto out;
455         if (!page_mapped(page))
456                 goto out;
457 
458         anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
459         root_anon_vma = ACCESS_ONCE(anon_vma->root);
460         if (down_read_trylock(&root_anon_vma->rwsem)) {
461                 /*
462                  * If the page is still mapped, then this anon_vma is still
463                  * its anon_vma, and holding the mutex ensures that it will
464                  * not go away, see anon_vma_free().
465                  */
466                 if (!page_mapped(page)) {
467                         up_read(&root_anon_vma->rwsem);
468                         anon_vma = NULL;
469                 }
470                 goto out;
471         }
472 
473         /* trylock failed, we got to sleep */
474         if (!atomic_inc_not_zero(&anon_vma->refcount)) {
475                 anon_vma = NULL;
476                 goto out;
477         }
478 
479         if (!page_mapped(page)) {
480                 put_anon_vma(anon_vma);
481                 anon_vma = NULL;
482                 goto out;
483         }
484 
485         /* we pinned the anon_vma, its safe to sleep */
486         rcu_read_unlock();
487         anon_vma_lock_read(anon_vma);
488 
489         if (atomic_dec_and_test(&anon_vma->refcount)) {
490                 /*
491                  * Oops, we held the last refcount, release the lock
492                  * and bail -- can't simply use put_anon_vma() because
493                  * we'll deadlock on the anon_vma_lock_write() recursion.
494                  */
495                 anon_vma_unlock_read(anon_vma);
496                 __put_anon_vma(anon_vma);
497                 anon_vma = NULL;
498         }
499 
500         return anon_vma;
501 
502 out:
503         rcu_read_unlock();
504         return anon_vma;
505 }
506 
507 void page_unlock_anon_vma_read(struct anon_vma *anon_vma)
508 {
509         anon_vma_unlock_read(anon_vma);
510 }
511 
512 /*
513  * At what user virtual address is page expected in @vma?
514  */
515 static inline unsigned long
516 __vma_address(struct page *page, struct vm_area_struct *vma)
517 {
518         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
519 
520         if (unlikely(is_vm_hugetlb_page(vma)))
521                 pgoff = page->index << huge_page_order(page_hstate(page));
522 
523         return vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
524 }
525 
526 inline unsigned long
527 vma_address(struct page *page, struct vm_area_struct *vma)
528 {
529         unsigned long address = __vma_address(page, vma);
530 
531         /* page should be within @vma mapping range */
532         VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
533 
534         return address;
535 }
536 
537 /*
538  * At what user virtual address is page expected in vma?
539  * Caller should check the page is actually part of the vma.
540  */
541 unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
542 {
543         unsigned long address;
544         if (PageAnon(page)) {
545                 struct anon_vma *page__anon_vma = page_anon_vma(page);
546                 /*
547                  * Note: swapoff's unuse_vma() is more efficient with this
548                  * check, and needs it to match anon_vma when KSM is active.
549                  */
550                 if (!vma->anon_vma || !page__anon_vma ||
551                     vma->anon_vma->root != page__anon_vma->root)
552                         return -EFAULT;
553         } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
554                 if (!vma->vm_file ||
555                     vma->vm_file->f_mapping != page->mapping)
556                         return -EFAULT;
557         } else
558                 return -EFAULT;
559         address = __vma_address(page, vma);
560         if (unlikely(address < vma->vm_start || address >= vma->vm_end))
561                 return -EFAULT;
562         return address;
563 }
564 
565 pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
566 {
567         pgd_t *pgd;
568         pud_t *pud;
569         pmd_t *pmd = NULL;
570 
571         pgd = pgd_offset(mm, address);
572         if (!pgd_present(*pgd))
573                 goto out;
574 
575         pud = pud_offset(pgd, address);
576         if (!pud_present(*pud))
577                 goto out;
578 
579         pmd = pmd_offset(pud, address);
580         if (!pmd_present(*pmd))
581                 pmd = NULL;
582 out:
583         return pmd;
584 }
585 
586 /*
587  * Check that @page is mapped at @address into @mm.
588  *
589  * If @sync is false, page_check_address may perform a racy check to avoid
590  * the page table lock when the pte is not present (helpful when reclaiming
591  * highly shared pages).
592  *
593  * On success returns with pte mapped and locked.
594  */
595 pte_t *__page_check_address(struct page *page, struct mm_struct *mm,
596                           unsigned long address, spinlock_t **ptlp, int sync)
597 {
598         pmd_t *pmd;
599         pte_t *pte;
600         spinlock_t *ptl;
601 
602         if (unlikely(PageHuge(page))) {
603                 pte = huge_pte_offset(mm, address);
604                 ptl = &mm->page_table_lock;
605                 goto check;
606         }
607 
608         pmd = mm_find_pmd(mm, address);
609         if (!pmd)
610                 return NULL;
611 
612         if (pmd_trans_huge(*pmd))
613                 return NULL;
614 
615         pte = pte_offset_map(pmd, address);
616         /* Make a quick check before getting the lock */
617         if (!sync && !pte_present(*pte)) {
618                 pte_unmap(pte);
619                 return NULL;
620         }
621 
622         ptl = pte_lockptr(mm, pmd);
623 check:
624         spin_lock(ptl);
625         if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
626                 *ptlp = ptl;
627                 return pte;
628         }
629         pte_unmap_unlock(pte, ptl);
630         return NULL;
631 }
632 
633 /**
634  * page_mapped_in_vma - check whether a page is really mapped in a VMA
635  * @page: the page to test
636  * @vma: the VMA to test
637  *
638  * Returns 1 if the page is mapped into the page tables of the VMA, 0
639  * if the page is not mapped into the page tables of this VMA.  Only
640  * valid for normal file or anonymous VMAs.
641  */
642 int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
643 {
644         unsigned long address;
645         pte_t *pte;
646         spinlock_t *ptl;
647 
648         address = __vma_address(page, vma);
649         if (unlikely(address < vma->vm_start || address >= vma->vm_end))
650                 return 0;
651         pte = page_check_address(page, vma->vm_mm, address, &ptl, 1);
652         if (!pte)                       /* the page is not in this mm */
653                 return 0;
654         pte_unmap_unlock(pte, ptl);
655 
656         return 1;
657 }
658 
659 /*
660  * Subfunctions of page_referenced: page_referenced_one called
661  * repeatedly from either page_referenced_anon or page_referenced_file.
662  */
663 int page_referenced_one(struct page *page, struct vm_area_struct *vma,
664                         unsigned long address, unsigned int *mapcount,
665                         unsigned long *vm_flags)
666 {
667         struct mm_struct *mm = vma->vm_mm;
668         int referenced = 0;
669 
670         if (unlikely(PageTransHuge(page))) {
671                 pmd_t *pmd;
672 
673                 spin_lock(&mm->page_table_lock);
674                 /*
675                  * rmap might return false positives; we must filter
676                  * these out using page_check_address_pmd().
677                  */
678                 pmd = page_check_address_pmd(page, mm, address,
679                                              PAGE_CHECK_ADDRESS_PMD_FLAG);
680                 if (!pmd) {
681                         spin_unlock(&mm->page_table_lock);
682                         goto out;
683                 }
684 
685                 if (vma->vm_flags & VM_LOCKED) {
686                         spin_unlock(&mm->page_table_lock);
687                         *mapcount = 0;  /* break early from loop */
688                         *vm_flags |= VM_LOCKED;
689                         goto out;
690                 }
691 
692                 /* go ahead even if the pmd is pmd_trans_splitting() */
693                 if (pmdp_clear_flush_young_notify(vma, address, pmd))
694                         referenced++;
695                 spin_unlock(&mm->page_table_lock);
696         } else {
697                 pte_t *pte;
698                 spinlock_t *ptl;
699 
700                 /*
701                  * rmap might return false positives; we must filter
702                  * these out using page_check_address().
703                  */
704                 pte = page_check_address(page, mm, address, &ptl, 0);
705                 if (!pte)
706                         goto out;
707 
708                 if (vma->vm_flags & VM_LOCKED) {
709                         pte_unmap_unlock(pte, ptl);
710                         *mapcount = 0;  /* break early from loop */
711                         *vm_flags |= VM_LOCKED;
712                         goto out;
713                 }
714 
715                 if (ptep_clear_flush_young_notify(vma, address, pte)) {
716                         /*
717                          * Don't treat a reference through a sequentially read
718                          * mapping as such.  If the page has been used in
719                          * another mapping, we will catch it; if this other
720                          * mapping is already gone, the unmap path will have
721                          * set PG_referenced or activated the page.
722                          */
723                         if (likely(!VM_SequentialReadHint(vma)))
724                                 referenced++;
725                 }
726                 pte_unmap_unlock(pte, ptl);
727         }
728 
729         (*mapcount)--;
730 
731         if (referenced)
732                 *vm_flags |= vma->vm_flags;
733 out:
734         return referenced;
735 }
736 
737 static int page_referenced_anon(struct page *page,
738                                 struct mem_cgroup *memcg,
739                                 unsigned long *vm_flags)
740 {
741         unsigned int mapcount;
742         struct anon_vma *anon_vma;
743         pgoff_t pgoff;
744         struct anon_vma_chain *avc;
745         int referenced = 0;
746 
747         anon_vma = page_lock_anon_vma_read(page);
748         if (!anon_vma)
749                 return referenced;
750 
751         mapcount = page_mapcount(page);
752         pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
753         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
754                 struct vm_area_struct *vma = avc->vma;
755                 unsigned long address = vma_address(page, vma);
756                 /*
757                  * If we are reclaiming on behalf of a cgroup, skip
758                  * counting on behalf of references from different
759                  * cgroups
760                  */
761                 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
762                         continue;
763                 referenced += page_referenced_one(page, vma, address,
764                                                   &mapcount, vm_flags);
765                 if (!mapcount)
766                         break;
767         }
768 
769         page_unlock_anon_vma_read(anon_vma);
770         return referenced;
771 }
772 
773 /**
774  * page_referenced_file - referenced check for object-based rmap
775  * @page: the page we're checking references on.
776  * @memcg: target memory control group
777  * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
778  *
779  * For an object-based mapped page, find all the places it is mapped and
780  * check/clear the referenced flag.  This is done by following the page->mapping
781  * pointer, then walking the chain of vmas it holds.  It returns the number
782  * of references it found.
783  *
784  * This function is only called from page_referenced for object-based pages.
785  */
786 static int page_referenced_file(struct page *page,
787                                 struct mem_cgroup *memcg,
788                                 unsigned long *vm_flags)
789 {
790         unsigned int mapcount;
791         struct address_space *mapping = page->mapping;
792         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
793         struct vm_area_struct *vma;
794         int referenced = 0;
795 
796         /*
797          * The caller's checks on page->mapping and !PageAnon have made
798          * sure that this is a file page: the check for page->mapping
799          * excludes the case just before it gets set on an anon page.
800          */
801         BUG_ON(PageAnon(page));
802 
803         /*
804          * The page lock not only makes sure that page->mapping cannot
805          * suddenly be NULLified by truncation, it makes sure that the
806          * structure at mapping cannot be freed and reused yet,
807          * so we can safely take mapping->i_mmap_mutex.
808          */
809         BUG_ON(!PageLocked(page));
810 
811         mutex_lock(&mapping->i_mmap_mutex);
812 
813         /*
814          * i_mmap_mutex does not stabilize mapcount at all, but mapcount
815          * is more likely to be accurate if we note it after spinning.
816          */
817         mapcount = page_mapcount(page);
818 
819         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
820                 unsigned long address = vma_address(page, vma);
821                 /*
822                  * If we are reclaiming on behalf of a cgroup, skip
823                  * counting on behalf of references from different
824                  * cgroups
825                  */
826                 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
827                         continue;
828                 referenced += page_referenced_one(page, vma, address,
829                                                   &mapcount, vm_flags);
830                 if (!mapcount)
831                         break;
832         }
833 
834         mutex_unlock(&mapping->i_mmap_mutex);
835         return referenced;
836 }
837 
838 /**
839  * page_referenced - test if the page was referenced
840  * @page: the page to test
841  * @is_locked: caller holds lock on the page
842  * @memcg: target memory cgroup
843  * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
844  *
845  * Quick test_and_clear_referenced for all mappings to a page,
846  * returns the number of ptes which referenced the page.
847  */
848 int page_referenced(struct page *page,
849                     int is_locked,
850                     struct mem_cgroup *memcg,
851                     unsigned long *vm_flags)
852 {
853         int referenced = 0;
854         int we_locked = 0;
855 
856         *vm_flags = 0;
857         if (page_mapped(page) && page_rmapping(page)) {
858                 if (!is_locked && (!PageAnon(page) || PageKsm(page))) {
859                         we_locked = trylock_page(page);
860                         if (!we_locked) {
861                                 referenced++;
862                                 goto out;
863                         }
864                 }
865                 if (unlikely(PageKsm(page)))
866                         referenced += page_referenced_ksm(page, memcg,
867                                                                 vm_flags);
868                 else if (PageAnon(page))
869                         referenced += page_referenced_anon(page, memcg,
870                                                                 vm_flags);
871                 else if (page->mapping)
872                         referenced += page_referenced_file(page, memcg,
873                                                                 vm_flags);
874                 if (we_locked)
875                         unlock_page(page);
876 
877                 if (page_test_and_clear_young(page_to_pfn(page)))
878                         referenced++;
879         }
880 out:
881         return referenced;
882 }
883 
884 static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
885                             unsigned long address)
886 {
887         struct mm_struct *mm = vma->vm_mm;
888         pte_t *pte;
889         spinlock_t *ptl;
890         int ret = 0;
891 
892         pte = page_check_address(page, mm, address, &ptl, 1);
893         if (!pte)
894                 goto out;
895 
896         if (pte_dirty(*pte) || pte_write(*pte)) {
897                 pte_t entry;
898 
899                 flush_cache_page(vma, address, pte_pfn(*pte));
900                 entry = ptep_clear_flush(vma, address, pte);
901                 entry = pte_wrprotect(entry);
902                 entry = pte_mkclean(entry);
903                 set_pte_at(mm, address, pte, entry);
904                 ret = 1;
905         }
906 
907         pte_unmap_unlock(pte, ptl);
908 
909         if (ret)
910                 mmu_notifier_invalidate_page(mm, address);
911 out:
912         return ret;
913 }
914 
915 static int page_mkclean_file(struct address_space *mapping, struct page *page)
916 {
917         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
918         struct vm_area_struct *vma;
919         int ret = 0;
920 
921         BUG_ON(PageAnon(page));
922 
923         mutex_lock(&mapping->i_mmap_mutex);
924         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
925                 if (vma->vm_flags & VM_SHARED) {
926                         unsigned long address = vma_address(page, vma);
927                         ret += page_mkclean_one(page, vma, address);
928                 }
929         }
930         mutex_unlock(&mapping->i_mmap_mutex);
931         return ret;
932 }
933 
934 int page_mkclean(struct page *page)
935 {
936         int ret = 0;
937 
938         BUG_ON(!PageLocked(page));
939 
940         if (page_mapped(page)) {
941                 struct address_space *mapping = page_mapping(page);
942                 if (mapping)
943                         ret = page_mkclean_file(mapping, page);
944         }
945 
946         return ret;
947 }
948 EXPORT_SYMBOL_GPL(page_mkclean);
949 
950 /**
951  * page_move_anon_rmap - move a page to our anon_vma
952  * @page:       the page to move to our anon_vma
953  * @vma:        the vma the page belongs to
954  * @address:    the user virtual address mapped
955  *
956  * When a page belongs exclusively to one process after a COW event,
957  * that page can be moved into the anon_vma that belongs to just that
958  * process, so the rmap code will not search the parent or sibling
959  * processes.
960  */
961 void page_move_anon_rmap(struct page *page,
962         struct vm_area_struct *vma, unsigned long address)
963 {
964         struct anon_vma *anon_vma = vma->anon_vma;
965 
966         VM_BUG_ON(!PageLocked(page));
967         VM_BUG_ON(!anon_vma);
968         VM_BUG_ON(page->index != linear_page_index(vma, address));
969 
970         anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
971         page->mapping = (struct address_space *) anon_vma;
972 }
973 
974 /**
975  * __page_set_anon_rmap - set up new anonymous rmap
976  * @page:       Page to add to rmap     
977  * @vma:        VM area to add page to.
978  * @address:    User virtual address of the mapping     
979  * @exclusive:  the page is exclusively owned by the current process
980  */
981 static void __page_set_anon_rmap(struct page *page,
982         struct vm_area_struct *vma, unsigned long address, int exclusive)
983 {
984         struct anon_vma *anon_vma = vma->anon_vma;
985 
986         BUG_ON(!anon_vma);
987 
988         if (PageAnon(page))
989                 return;
990 
991         /*
992          * If the page isn't exclusively mapped into this vma,
993          * we must use the _oldest_ possible anon_vma for the
994          * page mapping!
995          */
996         if (!exclusive)
997                 anon_vma = anon_vma->root;
998 
999         anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1000         page->mapping = (struct address_space *) anon_vma;
1001         page->index = linear_page_index(vma, address);
1002 }
1003 
1004 /**
1005  * __page_check_anon_rmap - sanity check anonymous rmap addition
1006  * @page:       the page to add the mapping to
1007  * @vma:        the vm area in which the mapping is added
1008  * @address:    the user virtual address mapped
1009  */
1010 static void __page_check_anon_rmap(struct page *page,
1011         struct vm_area_struct *vma, unsigned long address)
1012 {
1013 #ifdef CONFIG_DEBUG_VM
1014         /*
1015          * The page's anon-rmap details (mapping and index) are guaranteed to
1016          * be set up correctly at this point.
1017          *
1018          * We have exclusion against page_add_anon_rmap because the caller
1019          * always holds the page locked, except if called from page_dup_rmap,
1020          * in which case the page is already known to be setup.
1021          *
1022          * We have exclusion against page_add_new_anon_rmap because those pages
1023          * are initially only visible via the pagetables, and the pte is locked
1024          * over the call to page_add_new_anon_rmap.
1025          */
1026         BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root);
1027         BUG_ON(page->index != linear_page_index(vma, address));
1028 #endif
1029 }
1030 
1031 /**
1032  * page_add_anon_rmap - add pte mapping to an anonymous page
1033  * @page:       the page to add the mapping to
1034  * @vma:        the vm area in which the mapping is added
1035  * @address:    the user virtual address mapped
1036  *
1037  * The caller needs to hold the pte lock, and the page must be locked in
1038  * the anon_vma case: to serialize mapping,index checking after setting,
1039  * and to ensure that PageAnon is not being upgraded racily to PageKsm
1040  * (but PageKsm is never downgraded to PageAnon).
1041  */
1042 void page_add_anon_rmap(struct page *page,
1043         struct vm_area_struct *vma, unsigned long address)
1044 {
1045         do_page_add_anon_rmap(page, vma, address, 0);
1046 }
1047 
1048 /*
1049  * Special version of the above for do_swap_page, which often runs
1050  * into pages that are exclusively owned by the current process.
1051  * Everybody else should continue to use page_add_anon_rmap above.
1052  */
1053 void do_page_add_anon_rmap(struct page *page,
1054         struct vm_area_struct *vma, unsigned long address, int exclusive)
1055 {
1056         int first = atomic_inc_and_test(&page->_mapcount);
1057         if (first) {
1058                 if (!PageTransHuge(page))
1059                         __inc_zone_page_state(page, NR_ANON_PAGES);
1060                 else
1061                         __inc_zone_page_state(page,
1062                                               NR_ANON_TRANSPARENT_HUGEPAGES);
1063         }
1064         if (unlikely(PageKsm(page)))
1065                 return;
1066 
1067         VM_BUG_ON(!PageLocked(page));
1068         /* address might be in next vma when migration races vma_adjust */
1069         if (first)
1070                 __page_set_anon_rmap(page, vma, address, exclusive);
1071         else
1072                 __page_check_anon_rmap(page, vma, address);
1073 }
1074 
1075 /**
1076  * page_add_new_anon_rmap - add pte mapping to a new 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  *
1081  * Same as page_add_anon_rmap but must only be called on *new* pages.
1082  * This means the inc-and-test can be bypassed.
1083  * Page does not have to be locked.
1084  */
1085 void page_add_new_anon_rmap(struct page *page,
1086         struct vm_area_struct *vma, unsigned long address)
1087 {
1088         VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
1089         SetPageSwapBacked(page);
1090         atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
1091         if (!PageTransHuge(page))
1092                 __inc_zone_page_state(page, NR_ANON_PAGES);
1093         else
1094                 __inc_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
1095         __page_set_anon_rmap(page, vma, address, 1);
1096         if (!mlocked_vma_newpage(vma, page))
1097                 lru_cache_add_lru(page, LRU_ACTIVE_ANON);
1098         else
1099                 add_page_to_unevictable_list(page);
1100 }
1101 
1102 /**
1103  * page_add_file_rmap - add pte mapping to a file page
1104  * @page: the page to add the mapping to
1105  *
1106  * The caller needs to hold the pte lock.
1107  */
1108 void page_add_file_rmap(struct page *page)
1109 {
1110         bool locked;
1111         unsigned long flags;
1112 
1113         mem_cgroup_begin_update_page_stat(page, &locked, &flags);
1114         if (atomic_inc_and_test(&page->_mapcount)) {
1115                 __inc_zone_page_state(page, NR_FILE_MAPPED);
1116                 mem_cgroup_inc_page_stat(page, MEMCG_NR_FILE_MAPPED);
1117         }
1118         mem_cgroup_end_update_page_stat(page, &locked, &flags);
1119 }
1120 
1121 /**
1122  * page_remove_rmap - take down pte mapping from a page
1123  * @page: page to remove mapping from
1124  *
1125  * The caller needs to hold the pte lock.
1126  */
1127 void page_remove_rmap(struct page *page)
1128 {
1129         struct address_space *mapping = page_mapping(page);
1130         bool anon = PageAnon(page);
1131         bool locked;
1132         unsigned long flags;
1133 
1134         /*
1135          * The anon case has no mem_cgroup page_stat to update; but may
1136          * uncharge_page() below, where the lock ordering can deadlock if
1137          * we hold the lock against page_stat move: so avoid it on anon.
1138          */
1139         if (!anon)
1140                 mem_cgroup_begin_update_page_stat(page, &locked, &flags);
1141 
1142         /* page still mapped by someone else? */
1143         if (!atomic_add_negative(-1, &page->_mapcount))
1144                 goto out;
1145 
1146         /*
1147          * Now that the last pte has gone, s390 must transfer dirty
1148          * flag from storage key to struct page.  We can usually skip
1149          * this if the page is anon, so about to be freed; but perhaps
1150          * not if it's in swapcache - there might be another pte slot
1151          * containing the swap entry, but page not yet written to swap.
1152          *
1153          * And we can skip it on file pages, so long as the filesystem
1154          * participates in dirty tracking (note that this is not only an
1155          * optimization but also solves problems caused by dirty flag in
1156          * storage key getting set by a write from inside kernel); but need to
1157          * catch shm and tmpfs and ramfs pages which have been modified since
1158          * creation by read fault.
1159          *
1160          * Note that mapping must be decided above, before decrementing
1161          * mapcount (which luckily provides a barrier): once page is unmapped,
1162          * it could be truncated and page->mapping reset to NULL at any moment.
1163          * Note also that we are relying on page_mapping(page) to set mapping
1164          * to &swapper_space when PageSwapCache(page).
1165          */
1166         if (mapping && !mapping_cap_account_dirty(mapping) &&
1167             page_test_and_clear_dirty(page_to_pfn(page), 1))
1168                 set_page_dirty(page);
1169         /*
1170          * Hugepages are not counted in NR_ANON_PAGES nor NR_FILE_MAPPED
1171          * and not charged by memcg for now.
1172          */
1173         if (unlikely(PageHuge(page)))
1174                 goto out;
1175         if (anon) {
1176                 mem_cgroup_uncharge_page(page);
1177                 if (!PageTransHuge(page))
1178                         __dec_zone_page_state(page, NR_ANON_PAGES);
1179                 else
1180                         __dec_zone_page_state(page,
1181                                               NR_ANON_TRANSPARENT_HUGEPAGES);
1182         } else {
1183                 __dec_zone_page_state(page, NR_FILE_MAPPED);
1184                 mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
1185                 mem_cgroup_end_update_page_stat(page, &locked, &flags);
1186         }
1187         if (unlikely(PageMlocked(page)))
1188                 clear_page_mlock(page);
1189         /*
1190          * It would be tidy to reset the PageAnon mapping here,
1191          * but that might overwrite a racing page_add_anon_rmap
1192          * which increments mapcount after us but sets mapping
1193          * before us: so leave the reset to free_hot_cold_page,
1194          * and remember that it's only reliable while mapped.
1195          * Leaving it set also helps swapoff to reinstate ptes
1196          * faster for those pages still in swapcache.
1197          */
1198         return;
1199 out:
1200         if (!anon)
1201                 mem_cgroup_end_update_page_stat(page, &locked, &flags);
1202 }
1203 
1204 /*
1205  * Subfunctions of try_to_unmap: try_to_unmap_one called
1206  * repeatedly from try_to_unmap_ksm, try_to_unmap_anon or try_to_unmap_file.
1207  */
1208 int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
1209                      unsigned long address, enum ttu_flags flags)
1210 {
1211         struct mm_struct *mm = vma->vm_mm;
1212         pte_t *pte;
1213         pte_t pteval;
1214         spinlock_t *ptl;
1215         int ret = SWAP_AGAIN;
1216 
1217         pte = page_check_address(page, mm, address, &ptl, 0);
1218         if (!pte)
1219                 goto out;
1220 
1221         /*
1222          * If the page is mlock()d, we cannot swap it out.
1223          * If it's recently referenced (perhaps page_referenced
1224          * skipped over this mm) then we should reactivate it.
1225          */
1226         if (!(flags & TTU_IGNORE_MLOCK)) {
1227                 if (vma->vm_flags & VM_LOCKED)
1228                         goto out_mlock;
1229 
1230                 if (TTU_ACTION(flags) == TTU_MUNLOCK)
1231                         goto out_unmap;
1232         }
1233         if (!(flags & TTU_IGNORE_ACCESS)) {
1234                 if (ptep_clear_flush_young_notify(vma, address, pte)) {
1235                         ret = SWAP_FAIL;
1236                         goto out_unmap;
1237                 }
1238         }
1239 
1240         /* Nuke the page table entry. */
1241         flush_cache_page(vma, address, page_to_pfn(page));
1242         pteval = ptep_clear_flush(vma, address, pte);
1243 
1244         /* Move the dirty bit to the physical page now the pte is gone. */
1245         if (pte_dirty(pteval))
1246                 set_page_dirty(page);
1247 
1248         /* Update high watermark before we lower rss */
1249         update_hiwater_rss(mm);
1250 
1251         if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {
1252                 if (!PageHuge(page)) {
1253                         if (PageAnon(page))
1254                                 dec_mm_counter(mm, MM_ANONPAGES);
1255                         else
1256                                 dec_mm_counter(mm, MM_FILEPAGES);
1257                 }
1258                 set_pte_at(mm, address, pte,
1259                            swp_entry_to_pte(make_hwpoison_entry(page)));
1260         } else if (PageAnon(page)) {
1261                 swp_entry_t entry = { .val = page_private(page) };
1262 
1263                 if (PageSwapCache(page)) {
1264                         /*
1265                          * Store the swap location in the pte.
1266                          * See handle_pte_fault() ...
1267                          */
1268                         if (swap_duplicate(entry) < 0) {
1269                                 set_pte_at(mm, address, pte, pteval);
1270                                 ret = SWAP_FAIL;
1271                                 goto out_unmap;
1272                         }
1273                         if (list_empty(&mm->mmlist)) {
1274                                 spin_lock(&mmlist_lock);
1275                                 if (list_empty(&mm->mmlist))
1276                                         list_add(&mm->mmlist, &init_mm.mmlist);
1277                                 spin_unlock(&mmlist_lock);
1278                         }
1279                         dec_mm_counter(mm, MM_ANONPAGES);
1280                         inc_mm_counter(mm, MM_SWAPENTS);
1281                 } else if (IS_ENABLED(CONFIG_MIGRATION)) {
1282                         /*
1283                          * Store the pfn of the page in a special migration
1284                          * pte. do_swap_page() will wait until the migration
1285                          * pte is removed and then restart fault handling.
1286                          */
1287                         BUG_ON(TTU_ACTION(flags) != TTU_MIGRATION);
1288                         entry = make_migration_entry(page, pte_write(pteval));
1289                 }
1290                 set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
1291                 BUG_ON(pte_file(*pte));
1292         } else if (IS_ENABLED(CONFIG_MIGRATION) &&
1293                    (TTU_ACTION(flags) == TTU_MIGRATION)) {
1294                 /* Establish migration entry for a file page */
1295                 swp_entry_t entry;
1296                 entry = make_migration_entry(page, pte_write(pteval));
1297                 set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
1298         } else
1299                 dec_mm_counter(mm, MM_FILEPAGES);
1300 
1301         page_remove_rmap(page);
1302         page_cache_release(page);
1303 
1304 out_unmap:
1305         pte_unmap_unlock(pte, ptl);
1306         if (ret != SWAP_FAIL)
1307                 mmu_notifier_invalidate_page(mm, address);
1308 out:
1309         return ret;
1310 
1311 out_mlock:
1312         pte_unmap_unlock(pte, ptl);
1313 
1314 
1315         /*
1316          * We need mmap_sem locking, Otherwise VM_LOCKED check makes
1317          * unstable result and race. Plus, We can't wait here because
1318          * we now hold anon_vma->rwsem or mapping->i_mmap_mutex.
1319          * if trylock failed, the page remain in evictable lru and later
1320          * vmscan could retry to move the page to unevictable lru if the
1321          * page is actually mlocked.
1322          */
1323         if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
1324                 if (vma->vm_flags & VM_LOCKED) {
1325                         mlock_vma_page(page);
1326                         ret = SWAP_MLOCK;
1327                 }
1328                 up_read(&vma->vm_mm->mmap_sem);
1329         }
1330         return ret;
1331 }
1332 
1333 /*
1334  * objrmap doesn't work for nonlinear VMAs because the assumption that
1335  * offset-into-file correlates with offset-into-virtual-addresses does not hold.
1336  * Consequently, given a particular page and its ->index, we cannot locate the
1337  * ptes which are mapping that page without an exhaustive linear search.
1338  *
1339  * So what this code does is a mini "virtual scan" of each nonlinear VMA which
1340  * maps the file to which the target page belongs.  The ->vm_private_data field
1341  * holds the current cursor into that scan.  Successive searches will circulate
1342  * around the vma's virtual address space.
1343  *
1344  * So as more replacement pressure is applied to the pages in a nonlinear VMA,
1345  * more scanning pressure is placed against them as well.   Eventually pages
1346  * will become fully unmapped and are eligible for eviction.
1347  *
1348  * For very sparsely populated VMAs this is a little inefficient - chances are
1349  * there there won't be many ptes located within the scan cluster.  In this case
1350  * maybe we could scan further - to the end of the pte page, perhaps.
1351  *
1352  * Mlocked pages:  check VM_LOCKED under mmap_sem held for read, if we can
1353  * acquire it without blocking.  If vma locked, mlock the pages in the cluster,
1354  * rather than unmapping them.  If we encounter the "check_page" that vmscan is
1355  * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN.
1356  */
1357 #define CLUSTER_SIZE    min(32*PAGE_SIZE, PMD_SIZE)
1358 #define CLUSTER_MASK    (~(CLUSTER_SIZE - 1))
1359 
1360 static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
1361                 struct vm_area_struct *vma, struct page *check_page)
1362 {
1363         struct mm_struct *mm = vma->vm_mm;
1364         pmd_t *pmd;
1365         pte_t *pte;
1366         pte_t pteval;
1367         spinlock_t *ptl;
1368         struct page *page;
1369         unsigned long address;
1370         unsigned long mmun_start;       /* For mmu_notifiers */
1371         unsigned long mmun_end;         /* For mmu_notifiers */
1372         unsigned long end;
1373         int ret = SWAP_AGAIN;
1374         int locked_vma = 0;
1375 
1376         address = (vma->vm_start + cursor) & CLUSTER_MASK;
1377         end = address + CLUSTER_SIZE;
1378         if (address < vma->vm_start)
1379                 address = vma->vm_start;
1380         if (end > vma->vm_end)
1381                 end = vma->vm_end;
1382 
1383         pmd = mm_find_pmd(mm, address);
1384         if (!pmd)
1385                 return ret;
1386 
1387         mmun_start = address;
1388         mmun_end   = end;
1389         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1390 
1391         /*
1392          * If we can acquire the mmap_sem for read, and vma is VM_LOCKED,
1393          * keep the sem while scanning the cluster for mlocking pages.
1394          */
1395         if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
1396                 locked_vma = (vma->vm_flags & VM_LOCKED);
1397                 if (!locked_vma)
1398                         up_read(&vma->vm_mm->mmap_sem); /* don't need it */
1399         }
1400 
1401         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1402 
1403         /* Update high watermark before we lower rss */
1404         update_hiwater_rss(mm);
1405 
1406         for (; address < end; pte++, address += PAGE_SIZE) {
1407                 if (!pte_present(*pte))
1408                         continue;
1409                 page = vm_normal_page(vma, address, *pte);
1410                 BUG_ON(!page || PageAnon(page));
1411 
1412                 if (locked_vma) {
1413                         mlock_vma_page(page);   /* no-op if already mlocked */
1414                         if (page == check_page)
1415                                 ret = SWAP_MLOCK;
1416                         continue;       /* don't unmap */
1417                 }
1418 
1419                 if (ptep_clear_flush_young_notify(vma, address, pte))
1420                         continue;
1421 
1422                 /* Nuke the page table entry. */
1423                 flush_cache_page(vma, address, pte_pfn(*pte));
1424                 pteval = ptep_clear_flush(vma, address, pte);
1425 
1426                 /* If nonlinear, store the file page offset in the pte. */
1427                 if (page->index != linear_page_index(vma, address))
1428                         set_pte_at(mm, address, pte, pgoff_to_pte(page->index));
1429 
1430                 /* Move the dirty bit to the physical page now the pte is gone. */
1431                 if (pte_dirty(pteval))
1432                         set_page_dirty(page);
1433 
1434                 page_remove_rmap(page);
1435                 page_cache_release(page);
1436                 dec_mm_counter(mm, MM_FILEPAGES);
1437                 (*mapcount)--;
1438         }
1439         pte_unmap_unlock(pte - 1, ptl);
1440         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1441         if (locked_vma)
1442                 up_read(&vma->vm_mm->mmap_sem);
1443         return ret;
1444 }
1445 
1446 bool is_vma_temporary_stack(struct vm_area_struct *vma)
1447 {
1448         int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);
1449 
1450         if (!maybe_stack)
1451                 return false;
1452 
1453         if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
1454                                                 VM_STACK_INCOMPLETE_SETUP)
1455                 return true;
1456 
1457         return false;
1458 }
1459 
1460 /**
1461  * try_to_unmap_anon - unmap or unlock anonymous page using the object-based
1462  * rmap method
1463  * @page: the page to unmap/unlock
1464  * @flags: action and flags
1465  *
1466  * Find all the mappings of a page using the mapping pointer and the vma chains
1467  * contained in the anon_vma struct it points to.
1468  *
1469  * This function is only called from try_to_unmap/try_to_munlock for
1470  * anonymous pages.
1471  * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
1472  * where the page was found will be held for write.  So, we won't recheck
1473  * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
1474  * 'LOCKED.
1475  */
1476 static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
1477 {
1478         struct anon_vma *anon_vma;
1479         pgoff_t pgoff;
1480         struct anon_vma_chain *avc;
1481         int ret = SWAP_AGAIN;
1482 
1483         anon_vma = page_lock_anon_vma_read(page);
1484         if (!anon_vma)
1485                 return ret;
1486 
1487         pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1488         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1489                 struct vm_area_struct *vma = avc->vma;
1490                 unsigned long address;
1491 
1492                 /*
1493                  * During exec, a temporary VMA is setup and later moved.
1494                  * The VMA is moved under the anon_vma lock but not the
1495                  * page tables leading to a race where migration cannot
1496                  * find the migration ptes. Rather than increasing the
1497                  * locking requirements of exec(), migration skips
1498                  * temporary VMAs until after exec() completes.
1499                  */
1500                 if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) &&
1501                                 is_vma_temporary_stack(vma))
1502                         continue;
1503 
1504                 address = vma_address(page, vma);
1505                 ret = try_to_unmap_one(page, vma, address, flags);
1506                 if (ret != SWAP_AGAIN || !page_mapped(page))
1507                         break;
1508         }
1509 
1510         page_unlock_anon_vma_read(anon_vma);
1511         return ret;
1512 }
1513 
1514 /**
1515  * try_to_unmap_file - unmap/unlock file page using the object-based rmap method
1516  * @page: the page to unmap/unlock
1517  * @flags: action and flags
1518  *
1519  * Find all the mappings of a page using the mapping pointer and the vma chains
1520  * contained in the address_space struct it points to.
1521  *
1522  * This function is only called from try_to_unmap/try_to_munlock for
1523  * object-based pages.
1524  * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
1525  * where the page was found will be held for write.  So, we won't recheck
1526  * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
1527  * 'LOCKED.
1528  */
1529 static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
1530 {
1531         struct address_space *mapping = page->mapping;
1532         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1533         struct vm_area_struct *vma;
1534         int ret = SWAP_AGAIN;
1535         unsigned long cursor;
1536         unsigned long max_nl_cursor = 0;
1537         unsigned long max_nl_size = 0;
1538         unsigned int mapcount;
1539 
1540         mutex_lock(&mapping->i_mmap_mutex);
1541         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1542                 unsigned long address = vma_address(page, vma);
1543                 ret = try_to_unmap_one(page, vma, address, flags);
1544                 if (ret != SWAP_AGAIN || !page_mapped(page))
1545                         goto out;
1546         }
1547 
1548         if (list_empty(&mapping->i_mmap_nonlinear))
1549                 goto out;
1550 
1551         /*
1552          * We don't bother to try to find the munlocked page in nonlinears.
1553          * It's costly. Instead, later, page reclaim logic may call
1554          * try_to_unmap(TTU_MUNLOCK) and recover PG_mlocked lazily.
1555          */
1556         if (TTU_ACTION(flags) == TTU_MUNLOCK)
1557                 goto out;
1558 
1559         list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
1560                                                         shared.nonlinear) {
1561                 cursor = (unsigned long) vma->vm_private_data;
1562                 if (cursor > max_nl_cursor)
1563                         max_nl_cursor = cursor;
1564                 cursor = vma->vm_end - vma->vm_start;
1565                 if (cursor > max_nl_size)
1566                         max_nl_size = cursor;
1567         }
1568 
1569         if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */
1570                 ret = SWAP_FAIL;
1571                 goto out;
1572         }
1573 
1574         /*
1575          * We don't try to search for this page in the nonlinear vmas,
1576          * and page_referenced wouldn't have found it anyway.  Instead
1577          * just walk the nonlinear vmas trying to age and unmap some.
1578          * The mapcount of the page we came in with is irrelevant,
1579          * but even so use it as a guide to how hard we should try?
1580          */
1581         mapcount = page_mapcount(page);
1582         if (!mapcount)
1583                 goto out;
1584         cond_resched();
1585 
1586         max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
1587         if (max_nl_cursor == 0)
1588                 max_nl_cursor = CLUSTER_SIZE;
1589 
1590         do {
1591                 list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
1592                                                         shared.nonlinear) {
1593                         cursor = (unsigned long) vma->vm_private_data;
1594                         while ( cursor < max_nl_cursor &&
1595                                 cursor < vma->vm_end - vma->vm_start) {
1596                                 if (try_to_unmap_cluster(cursor, &mapcount,
1597                                                 vma, page) == SWAP_MLOCK)
1598                                         ret = SWAP_MLOCK;
1599                                 cursor += CLUSTER_SIZE;
1600                                 vma->vm_private_data = (void *) cursor;
1601                                 if ((int)mapcount <= 0)
1602                                         goto out;
1603                         }
1604                         vma->vm_private_data = (void *) max_nl_cursor;
1605                 }
1606                 cond_resched();
1607                 max_nl_cursor += CLUSTER_SIZE;
1608         } while (max_nl_cursor <= max_nl_size);
1609 
1610         /*
1611          * Don't loop forever (perhaps all the remaining pages are
1612          * in locked vmas).  Reset cursor on all unreserved nonlinear
1613          * vmas, now forgetting on which ones it had fallen behind.
1614          */
1615         list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.nonlinear)
1616                 vma->vm_private_data = NULL;
1617 out:
1618         mutex_unlock(&mapping->i_mmap_mutex);
1619         return ret;
1620 }
1621 
1622 /**
1623  * try_to_unmap - try to remove all page table mappings to a page
1624  * @page: the page to get unmapped
1625  * @flags: action and flags
1626  *
1627  * Tries to remove all the page table entries which are mapping this
1628  * page, used in the pageout path.  Caller must hold the page lock.
1629  * Return values are:
1630  *
1631  * SWAP_SUCCESS - we succeeded in removing all mappings
1632  * SWAP_AGAIN   - we missed a mapping, try again later
1633  * SWAP_FAIL    - the page is unswappable
1634  * SWAP_MLOCK   - page is mlocked.
1635  */
1636 int try_to_unmap(struct page *page, enum ttu_flags flags)
1637 {
1638         int ret;
1639 
1640         BUG_ON(!PageLocked(page));
1641         VM_BUG_ON(!PageHuge(page) && PageTransHuge(page));
1642 
1643         if (unlikely(PageKsm(page)))
1644                 ret = try_to_unmap_ksm(page, flags);
1645         else if (PageAnon(page))
1646                 ret = try_to_unmap_anon(page, flags);
1647         else
1648                 ret = try_to_unmap_file(page, flags);
1649         if (ret != SWAP_MLOCK && !page_mapped(page))
1650                 ret = SWAP_SUCCESS;
1651         return ret;
1652 }
1653 
1654 /**
1655  * try_to_munlock - try to munlock a page
1656  * @page: the page to be munlocked
1657  *
1658  * Called from munlock code.  Checks all of the VMAs mapping the page
1659  * to make sure nobody else has this page mlocked. The page will be
1660  * returned with PG_mlocked cleared if no other vmas have it mlocked.
1661  *
1662  * Return values are:
1663  *
1664  * SWAP_AGAIN   - no vma is holding page mlocked, or,
1665  * SWAP_AGAIN   - page mapped in mlocked vma -- couldn't acquire mmap sem
1666  * SWAP_FAIL    - page cannot be located at present
1667  * SWAP_MLOCK   - page is now mlocked.
1668  */
1669 int try_to_munlock(struct page *page)
1670 {
1671         VM_BUG_ON(!PageLocked(page) || PageLRU(page));
1672 
1673         if (unlikely(PageKsm(page)))
1674                 return try_to_unmap_ksm(page, TTU_MUNLOCK);
1675         else if (PageAnon(page))
1676                 return try_to_unmap_anon(page, TTU_MUNLOCK);
1677         else
1678                 return try_to_unmap_file(page, TTU_MUNLOCK);
1679 }
1680 
1681 void __put_anon_vma(struct anon_vma *anon_vma)
1682 {
1683         struct anon_vma *root = anon_vma->root;
1684 
1685         if (root != anon_vma && atomic_dec_and_test(&root->refcount))
1686                 anon_vma_free(root);
1687 
1688         anon_vma_free(anon_vma);
1689 }
1690 
1691 #ifdef CONFIG_MIGRATION
1692 /*
1693  * rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file():
1694  * Called by migrate.c to remove migration ptes, but might be used more later.
1695  */
1696 static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
1697                 struct vm_area_struct *, unsigned long, void *), void *arg)
1698 {
1699         struct anon_vma *anon_vma;
1700         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1701         struct anon_vma_chain *avc;
1702         int ret = SWAP_AGAIN;
1703 
1704         /*
1705          * Note: remove_migration_ptes() cannot use page_lock_anon_vma_read()
1706          * because that depends on page_mapped(); but not all its usages
1707          * are holding mmap_sem. Users without mmap_sem are required to
1708          * take a reference count to prevent the anon_vma disappearing
1709          */
1710         anon_vma = page_anon_vma(page);
1711         if (!anon_vma)
1712                 return ret;
1713         anon_vma_lock_read(anon_vma);
1714         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1715                 struct vm_area_struct *vma = avc->vma;
1716                 unsigned long address = vma_address(page, vma);
1717                 ret = rmap_one(page, vma, address, arg);
1718                 if (ret != SWAP_AGAIN)
1719                         break;
1720         }
1721         anon_vma_unlock_read(anon_vma);
1722         return ret;
1723 }
1724 
1725 static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *,
1726                 struct vm_area_struct *, unsigned long, void *), void *arg)
1727 {
1728         struct address_space *mapping = page->mapping;
1729         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1730         struct vm_area_struct *vma;
1731         int ret = SWAP_AGAIN;
1732 
1733         if (!mapping)
1734                 return ret;
1735         mutex_lock(&mapping->i_mmap_mutex);
1736         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1737                 unsigned long address = vma_address(page, vma);
1738                 ret = rmap_one(page, vma, address, arg);
1739                 if (ret != SWAP_AGAIN)
1740                         break;
1741         }
1742         /*
1743          * No nonlinear handling: being always shared, nonlinear vmas
1744          * never contain migration ptes.  Decide what to do about this
1745          * limitation to linear when we need rmap_walk() on nonlinear.
1746          */
1747         mutex_unlock(&mapping->i_mmap_mutex);
1748         return ret;
1749 }
1750 
1751 int rmap_walk(struct page *page, int (*rmap_one)(struct page *,
1752                 struct vm_area_struct *, unsigned long, void *), void *arg)
1753 {
1754         VM_BUG_ON(!PageLocked(page));
1755 
1756         if (unlikely(PageKsm(page)))
1757                 return rmap_walk_ksm(page, rmap_one, arg);
1758         else if (PageAnon(page))
1759                 return rmap_walk_anon(page, rmap_one, arg);
1760         else
1761                 return rmap_walk_file(page, rmap_one, arg);
1762 }
1763 #endif /* CONFIG_MIGRATION */
1764 
1765 #ifdef CONFIG_HUGETLB_PAGE
1766 /*
1767  * The following three functions are for anonymous (private mapped) hugepages.
1768  * Unlike common anonymous pages, anonymous hugepages have no accounting code
1769  * and no lru code, because we handle hugepages differently from common pages.
1770  */
1771 static void __hugepage_set_anon_rmap(struct page *page,
1772         struct vm_area_struct *vma, unsigned long address, int exclusive)
1773 {
1774         struct anon_vma *anon_vma = vma->anon_vma;
1775 
1776         BUG_ON(!anon_vma);
1777 
1778         if (PageAnon(page))
1779                 return;
1780         if (!exclusive)
1781                 anon_vma = anon_vma->root;
1782 
1783         anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1784         page->mapping = (struct address_space *) anon_vma;
1785         page->index = linear_page_index(vma, address);
1786 }
1787 
1788 void hugepage_add_anon_rmap(struct page *page,
1789                             struct vm_area_struct *vma, unsigned long address)
1790 {
1791         struct anon_vma *anon_vma = vma->anon_vma;
1792         int first;
1793 
1794         BUG_ON(!PageLocked(page));
1795         BUG_ON(!anon_vma);
1796         /* address might be in next vma when migration races vma_adjust */
1797         first = atomic_inc_and_test(&page->_mapcount);
1798         if (first)
1799                 __hugepage_set_anon_rmap(page, vma, address, 0);
1800 }
1801 
1802 void hugepage_add_new_anon_rmap(struct page *page,
1803                         struct vm_area_struct *vma, unsigned long address)
1804 {
1805         BUG_ON(address < vma->vm_start || address >= vma->vm_end);
1806         atomic_set(&page->_mapcount, 0);
1807         __hugepage_set_anon_rmap(page, vma, address, 1);
1808 }
1809 #endif /* CONFIG_HUGETLB_PAGE */
1810 

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