Version:  2.0.40 2.2.26 2.4.37 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16

Linux/mm/rmap.c

  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->mutex
 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->mutex,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 
 60 #include <asm/tlbflush.h>
 61 
 62 #include "internal.h"
 63 
 64 static struct kmem_cache *anon_vma_cachep;
 65 static struct kmem_cache *anon_vma_chain_cachep;
 66 
 67 static inline struct anon_vma *anon_vma_alloc(void)
 68 {
 69         struct anon_vma *anon_vma;
 70 
 71         anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
 72         if (anon_vma) {
 73                 atomic_set(&anon_vma->refcount, 1);
 74                 /*
 75                  * Initialise the anon_vma root to point to itself. If called
 76                  * from fork, the root will be reset to the parents anon_vma.
 77                  */
 78                 anon_vma->root = anon_vma;
 79         }
 80 
 81         return anon_vma;
 82 }
 83 
 84 static inline void anon_vma_free(struct anon_vma *anon_vma)
 85 {
 86         VM_BUG_ON(atomic_read(&anon_vma->refcount));
 87 
 88         /*
 89          * Synchronize against page_lock_anon_vma() such that
 90          * we can safely hold the lock without the anon_vma getting
 91          * freed.
 92          *
 93          * Relies on the full mb implied by the atomic_dec_and_test() from
 94          * put_anon_vma() against the acquire barrier implied by
 95          * mutex_trylock() from page_lock_anon_vma(). This orders:
 96          *
 97          * page_lock_anon_vma()         VS      put_anon_vma()
 98          *   mutex_trylock()                      atomic_dec_and_test()
 99          *   LOCK                                 MB
100          *   atomic_read()                        mutex_is_locked()
101          *
102          * LOCK should suffice since the actual taking of the lock must
103          * happen _before_ what follows.
104          */
105         if (mutex_is_locked(&anon_vma->root->mutex)) {
106                 anon_vma_lock(anon_vma);
107                 anon_vma_unlock(anon_vma);
108         }
109 
110         kmem_cache_free(anon_vma_cachep, anon_vma);
111 }
112 
113 static inline struct anon_vma_chain *anon_vma_chain_alloc(gfp_t gfp)
114 {
115         return kmem_cache_alloc(anon_vma_chain_cachep, gfp);
116 }
117 
118 static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
119 {
120         kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain);
121 }
122 
123 static void anon_vma_chain_link(struct vm_area_struct *vma,
124                                 struct anon_vma_chain *avc,
125                                 struct anon_vma *anon_vma)
126 {
127         avc->vma = vma;
128         avc->anon_vma = anon_vma;
129         list_add(&avc->same_vma, &vma->anon_vma_chain);
130 
131         /*
132          * It's critical to add new vmas to the tail of the anon_vma,
133          * see comment in huge_memory.c:__split_huge_page().
134          */
135         list_add_tail(&avc->same_anon_vma, &anon_vma->head);
136 }
137 
138 /**
139  * anon_vma_prepare - attach an anon_vma to a memory region
140  * @vma: the memory region in question
141  *
142  * This makes sure the memory mapping described by 'vma' has
143  * an 'anon_vma' attached to it, so that we can associate the
144  * anonymous pages mapped into it with that anon_vma.
145  *
146  * The common case will be that we already have one, but if
147  * not we either need to find an adjacent mapping that we
148  * can re-use the anon_vma from (very common when the only
149  * reason for splitting a vma has been mprotect()), or we
150  * allocate a new one.
151  *
152  * Anon-vma allocations are very subtle, because we may have
153  * optimistically looked up an anon_vma in page_lock_anon_vma()
154  * and that may actually touch the spinlock even in the newly
155  * allocated vma (it depends on RCU to make sure that the
156  * anon_vma isn't actually destroyed).
157  *
158  * As a result, we need to do proper anon_vma locking even
159  * for the new allocation. At the same time, we do not want
160  * to do any locking for the common case of already having
161  * an anon_vma.
162  *
163  * This must be called with the mmap_sem held for reading.
164  */
165 int anon_vma_prepare(struct vm_area_struct *vma)
166 {
167         struct anon_vma *anon_vma = vma->anon_vma;
168         struct anon_vma_chain *avc;
169 
170         might_sleep();
171         if (unlikely(!anon_vma)) {
172                 struct mm_struct *mm = vma->vm_mm;
173                 struct anon_vma *allocated;
174 
175                 avc = anon_vma_chain_alloc(GFP_KERNEL);
176                 if (!avc)
177                         goto out_enomem;
178 
179                 anon_vma = find_mergeable_anon_vma(vma);
180                 allocated = NULL;
181                 if (!anon_vma) {
182                         anon_vma = anon_vma_alloc();
183                         if (unlikely(!anon_vma))
184                                 goto out_enomem_free_avc;
185                         allocated = anon_vma;
186                 }
187 
188                 anon_vma_lock(anon_vma);
189                 /* page_table_lock to protect against threads */
190                 spin_lock(&mm->page_table_lock);
191                 if (likely(!vma->anon_vma)) {
192                         vma->anon_vma = anon_vma;
193                         anon_vma_chain_link(vma, avc, anon_vma);
194                         allocated = NULL;
195                         avc = NULL;
196                 }
197                 spin_unlock(&mm->page_table_lock);
198                 anon_vma_unlock(anon_vma);
199 
200                 if (unlikely(allocated))
201                         put_anon_vma(allocated);
202                 if (unlikely(avc))
203                         anon_vma_chain_free(avc);
204         }
205         return 0;
206 
207  out_enomem_free_avc:
208         anon_vma_chain_free(avc);
209  out_enomem:
210         return -ENOMEM;
211 }
212 
213 /*
214  * This is a useful helper function for locking the anon_vma root as
215  * we traverse the vma->anon_vma_chain, looping over anon_vma's that
216  * have the same vma.
217  *
218  * Such anon_vma's should have the same root, so you'd expect to see
219  * just a single mutex_lock for the whole traversal.
220  */
221 static inline struct anon_vma *lock_anon_vma_root(struct anon_vma *root, struct anon_vma *anon_vma)
222 {
223         struct anon_vma *new_root = anon_vma->root;
224         if (new_root != root) {
225                 if (WARN_ON_ONCE(root))
226                         mutex_unlock(&root->mutex);
227                 root = new_root;
228                 mutex_lock(&root->mutex);
229         }
230         return root;
231 }
232 
233 static inline void unlock_anon_vma_root(struct anon_vma *root)
234 {
235         if (root)
236                 mutex_unlock(&root->mutex);
237 }
238 
239 /*
240  * Attach the anon_vmas from src to dst.
241  * Returns 0 on success, -ENOMEM on failure.
242  */
243 int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
244 {
245         struct anon_vma_chain *avc, *pavc;
246         struct anon_vma *root = NULL;
247 
248         list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
249                 struct anon_vma *anon_vma;
250 
251                 avc = anon_vma_chain_alloc(GFP_NOWAIT | __GFP_NOWARN);
252                 if (unlikely(!avc)) {
253                         unlock_anon_vma_root(root);
254                         root = NULL;
255                         avc = anon_vma_chain_alloc(GFP_KERNEL);
256                         if (!avc)
257                                 goto enomem_failure;
258                 }
259                 anon_vma = pavc->anon_vma;
260                 root = lock_anon_vma_root(root, anon_vma);
261                 anon_vma_chain_link(dst, avc, anon_vma);
262         }
263         unlock_anon_vma_root(root);
264         return 0;
265 
266  enomem_failure:
267         unlink_anon_vmas(dst);
268         return -ENOMEM;
269 }
270 
271 /*
272  * Some rmap walk that needs to find all ptes/hugepmds without false
273  * negatives (like migrate and split_huge_page) running concurrent
274  * with operations that copy or move pagetables (like mremap() and
275  * fork()) to be safe. They depend on the anon_vma "same_anon_vma"
276  * list to be in a certain order: the dst_vma must be placed after the
277  * src_vma in the list. This is always guaranteed by fork() but
278  * mremap() needs to call this function to enforce it in case the
279  * dst_vma isn't newly allocated and chained with the anon_vma_clone()
280  * function but just an extension of a pre-existing vma through
281  * vma_merge.
282  *
283  * NOTE: the same_anon_vma list can still be changed by other
284  * processes while mremap runs because mremap doesn't hold the
285  * anon_vma mutex to prevent modifications to the list while it
286  * runs. All we need to enforce is that the relative order of this
287  * process vmas isn't changing (we don't care about other vmas
288  * order). Each vma corresponds to an anon_vma_chain structure so
289  * there's no risk that other processes calling anon_vma_moveto_tail()
290  * and changing the same_anon_vma list under mremap() will screw with
291  * the relative order of this process vmas in the list, because we
292  * they can't alter the order of any vma that belongs to this
293  * process. And there can't be another anon_vma_moveto_tail() running
294  * concurrently with mremap() coming from this process because we hold
295  * the mmap_sem for the whole mremap(). fork() ordering dependency
296  * also shouldn't be affected because fork() only cares that the
297  * parent vmas are placed in the list before the child vmas and
298  * anon_vma_moveto_tail() won't reorder vmas from either the fork()
299  * parent or child.
300  */
301 void anon_vma_moveto_tail(struct vm_area_struct *dst)
302 {
303         struct anon_vma_chain *pavc;
304         struct anon_vma *root = NULL;
305 
306         list_for_each_entry_reverse(pavc, &dst->anon_vma_chain, same_vma) {
307                 struct anon_vma *anon_vma = pavc->anon_vma;
308                 VM_BUG_ON(pavc->vma != dst);
309                 root = lock_anon_vma_root(root, anon_vma);
310                 list_del(&pavc->same_anon_vma);
311                 list_add_tail(&pavc->same_anon_vma, &anon_vma->head);
312         }
313         unlock_anon_vma_root(root);
314 }
315 
316 /*
317  * Attach vma to its own anon_vma, as well as to the anon_vmas that
318  * the corresponding VMA in the parent process is attached to.
319  * Returns 0 on success, non-zero on failure.
320  */
321 int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
322 {
323         struct anon_vma_chain *avc;
324         struct anon_vma *anon_vma;
325 
326         /* Don't bother if the parent process has no anon_vma here. */
327         if (!pvma->anon_vma)
328                 return 0;
329 
330         /*
331          * First, attach the new VMA to the parent VMA's anon_vmas,
332          * so rmap can find non-COWed pages in child processes.
333          */
334         if (anon_vma_clone(vma, pvma))
335                 return -ENOMEM;
336 
337         /* Then add our own anon_vma. */
338         anon_vma = anon_vma_alloc();
339         if (!anon_vma)
340                 goto out_error;
341         avc = anon_vma_chain_alloc(GFP_KERNEL);
342         if (!avc)
343                 goto out_error_free_anon_vma;
344 
345         /*
346          * The root anon_vma's spinlock is the lock actually used when we
347          * lock any of the anon_vmas in this anon_vma tree.
348          */
349         anon_vma->root = pvma->anon_vma->root;
350         /*
351          * With refcounts, an anon_vma can stay around longer than the
352          * process it belongs to. The root anon_vma needs to be pinned until
353          * this anon_vma is freed, because the lock lives in the root.
354          */
355         get_anon_vma(anon_vma->root);
356         /* Mark this anon_vma as the one where our new (COWed) pages go. */
357         vma->anon_vma = anon_vma;
358         anon_vma_lock(anon_vma);
359         anon_vma_chain_link(vma, avc, anon_vma);
360         anon_vma_unlock(anon_vma);
361 
362         return 0;
363 
364  out_error_free_anon_vma:
365         put_anon_vma(anon_vma);
366  out_error:
367         unlink_anon_vmas(vma);
368         return -ENOMEM;
369 }
370 
371 void unlink_anon_vmas(struct vm_area_struct *vma)
372 {
373         struct anon_vma_chain *avc, *next;
374         struct anon_vma *root = NULL;
375 
376         /*
377          * Unlink each anon_vma chained to the VMA.  This list is ordered
378          * from newest to oldest, ensuring the root anon_vma gets freed last.
379          */
380         list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
381                 struct anon_vma *anon_vma = avc->anon_vma;
382 
383                 root = lock_anon_vma_root(root, anon_vma);
384                 list_del(&avc->same_anon_vma);
385 
386                 /*
387                  * Leave empty anon_vmas on the list - we'll need
388                  * to free them outside the lock.
389                  */
390                 if (list_empty(&anon_vma->head))
391                         continue;
392 
393                 list_del(&avc->same_vma);
394                 anon_vma_chain_free(avc);
395         }
396         unlock_anon_vma_root(root);
397 
398         /*
399          * Iterate the list once more, it now only contains empty and unlinked
400          * anon_vmas, destroy them. Could not do before due to __put_anon_vma()
401          * needing to acquire the anon_vma->root->mutex.
402          */
403         list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
404                 struct anon_vma *anon_vma = avc->anon_vma;
405 
406                 put_anon_vma(anon_vma);
407 
408                 list_del(&avc->same_vma);
409                 anon_vma_chain_free(avc);
410         }
411 }
412 
413 static void anon_vma_ctor(void *data)
414 {
415         struct anon_vma *anon_vma = data;
416 
417         mutex_init(&anon_vma->mutex);
418         atomic_set(&anon_vma->refcount, 0);
419         INIT_LIST_HEAD(&anon_vma->head);
420 }
421 
422 void __init anon_vma_init(void)
423 {
424         anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
425                         0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor);
426         anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC);
427 }
428 
429 /*
430  * Getting a lock on a stable anon_vma from a page off the LRU is tricky!
431  *
432  * Since there is no serialization what so ever against page_remove_rmap()
433  * the best this function can do is return a locked anon_vma that might
434  * have been relevant to this page.
435  *
436  * The page might have been remapped to a different anon_vma or the anon_vma
437  * returned may already be freed (and even reused).
438  *
439  * In case it was remapped to a different anon_vma, the new anon_vma will be a
440  * child of the old anon_vma, and the anon_vma lifetime rules will therefore
441  * ensure that any anon_vma obtained from the page will still be valid for as
442  * long as we observe page_mapped() [ hence all those page_mapped() tests ].
443  *
444  * All users of this function must be very careful when walking the anon_vma
445  * chain and verify that the page in question is indeed mapped in it
446  * [ something equivalent to page_mapped_in_vma() ].
447  *
448  * Since anon_vma's slab is DESTROY_BY_RCU and we know from page_remove_rmap()
449  * that the anon_vma pointer from page->mapping is valid if there is a
450  * mapcount, we can dereference the anon_vma after observing those.
451  */
452 struct anon_vma *page_get_anon_vma(struct page *page)
453 {
454         struct anon_vma *anon_vma = NULL;
455         unsigned long anon_mapping;
456 
457         rcu_read_lock();
458         anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
459         if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
460                 goto out;
461         if (!page_mapped(page))
462                 goto out;
463 
464         anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
465         if (!atomic_inc_not_zero(&anon_vma->refcount)) {
466                 anon_vma = NULL;
467                 goto out;
468         }
469 
470         /*
471          * If this page is still mapped, then its anon_vma cannot have been
472          * freed.  But if it has been unmapped, we have no security against the
473          * anon_vma structure being freed and reused (for another anon_vma:
474          * SLAB_DESTROY_BY_RCU guarantees that - so the atomic_inc_not_zero()
475          * above cannot corrupt).
476          */
477         if (!page_mapped(page)) {
478                 put_anon_vma(anon_vma);
479                 anon_vma = NULL;
480         }
481 out:
482         rcu_read_unlock();
483 
484         return anon_vma;
485 }
486 
487 /*
488  * Similar to page_get_anon_vma() except it locks the anon_vma.
489  *
490  * Its a little more complex as it tries to keep the fast path to a single
491  * atomic op -- the trylock. If we fail the trylock, we fall back to getting a
492  * reference like with page_get_anon_vma() and then block on the mutex.
493  */
494 struct anon_vma *page_lock_anon_vma(struct page *page)
495 {
496         struct anon_vma *anon_vma = NULL;
497         struct anon_vma *root_anon_vma;
498         unsigned long anon_mapping;
499 
500         rcu_read_lock();
501         anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
502         if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
503                 goto out;
504         if (!page_mapped(page))
505                 goto out;
506 
507         anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
508         root_anon_vma = ACCESS_ONCE(anon_vma->root);
509         if (mutex_trylock(&root_anon_vma->mutex)) {
510                 /*
511                  * If the page is still mapped, then this anon_vma is still
512                  * its anon_vma, and holding the mutex ensures that it will
513                  * not go away, see anon_vma_free().
514                  */
515                 if (!page_mapped(page)) {
516                         mutex_unlock(&root_anon_vma->mutex);
517                         anon_vma = NULL;
518                 }
519                 goto out;
520         }
521 
522         /* trylock failed, we got to sleep */
523         if (!atomic_inc_not_zero(&anon_vma->refcount)) {
524                 anon_vma = NULL;
525                 goto out;
526         }
527 
528         if (!page_mapped(page)) {
529                 put_anon_vma(anon_vma);
530                 anon_vma = NULL;
531                 goto out;
532         }
533 
534         /* we pinned the anon_vma, its safe to sleep */
535         rcu_read_unlock();
536         anon_vma_lock(anon_vma);
537 
538         if (atomic_dec_and_test(&anon_vma->refcount)) {
539                 /*
540                  * Oops, we held the last refcount, release the lock
541                  * and bail -- can't simply use put_anon_vma() because
542                  * we'll deadlock on the anon_vma_lock() recursion.
543                  */
544                 anon_vma_unlock(anon_vma);
545                 __put_anon_vma(anon_vma);
546                 anon_vma = NULL;
547         }
548 
549         return anon_vma;
550 
551 out:
552         rcu_read_unlock();
553         return anon_vma;
554 }
555 
556 void page_unlock_anon_vma(struct anon_vma *anon_vma)
557 {
558         anon_vma_unlock(anon_vma);
559 }
560 
561 /*
562  * At what user virtual address is page expected in @vma?
563  * Returns virtual address or -EFAULT if page's index/offset is not
564  * within the range mapped the @vma.
565  */
566 inline unsigned long
567 vma_address(struct page *page, struct vm_area_struct *vma)
568 {
569         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
570         unsigned long address;
571 
572         if (unlikely(is_vm_hugetlb_page(vma)))
573                 pgoff = page->index << huge_page_order(page_hstate(page));
574         address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
575         if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
576                 /* page should be within @vma mapping range */
577                 return -EFAULT;
578         }
579         return address;
580 }
581 
582 /*
583  * At what user virtual address is page expected in vma?
584  * Caller should check the page is actually part of the vma.
585  */
586 unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
587 {
588         if (PageAnon(page)) {
589                 struct anon_vma *page__anon_vma = page_anon_vma(page);
590                 /*
591                  * Note: swapoff's unuse_vma() is more efficient with this
592                  * check, and needs it to match anon_vma when KSM is active.
593                  */
594                 if (!vma->anon_vma || !page__anon_vma ||
595                     vma->anon_vma->root != page__anon_vma->root)
596                         return -EFAULT;
597         } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
598                 if (!vma->vm_file ||
599                     vma->vm_file->f_mapping != page->mapping)
600                         return -EFAULT;
601         } else
602                 return -EFAULT;
603         return vma_address(page, vma);
604 }
605 
606 /*
607  * Check that @page is mapped at @address into @mm.
608  *
609  * If @sync is false, page_check_address may perform a racy check to avoid
610  * the page table lock when the pte is not present (helpful when reclaiming
611  * highly shared pages).
612  *
613  * On success returns with pte mapped and locked.
614  */
615 pte_t *__page_check_address(struct page *page, struct mm_struct *mm,
616                           unsigned long address, spinlock_t **ptlp, int sync)
617 {
618         pgd_t *pgd;
619         pud_t *pud;
620         pmd_t *pmd;
621         pte_t *pte;
622         spinlock_t *ptl;
623 
624         if (unlikely(PageHuge(page))) {
625                 pte = huge_pte_offset(mm, address);
626                 ptl = &mm->page_table_lock;
627                 goto check;
628         }
629 
630         pgd = pgd_offset(mm, address);
631         if (!pgd_present(*pgd))
632                 return NULL;
633 
634         pud = pud_offset(pgd, address);
635         if (!pud_present(*pud))
636                 return NULL;
637 
638         pmd = pmd_offset(pud, address);
639         if (!pmd_present(*pmd))
640                 return NULL;
641         if (pmd_trans_huge(*pmd))
642                 return NULL;
643 
644         pte = pte_offset_map(pmd, address);
645         /* Make a quick check before getting the lock */
646         if (!sync && !pte_present(*pte)) {
647                 pte_unmap(pte);
648                 return NULL;
649         }
650 
651         ptl = pte_lockptr(mm, pmd);
652 check:
653         spin_lock(ptl);
654         if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
655                 *ptlp = ptl;
656                 return pte;
657         }
658         pte_unmap_unlock(pte, ptl);
659         return NULL;
660 }
661 
662 /**
663  * page_mapped_in_vma - check whether a page is really mapped in a VMA
664  * @page: the page to test
665  * @vma: the VMA to test
666  *
667  * Returns 1 if the page is mapped into the page tables of the VMA, 0
668  * if the page is not mapped into the page tables of this VMA.  Only
669  * valid for normal file or anonymous VMAs.
670  */
671 int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
672 {
673         unsigned long address;
674         pte_t *pte;
675         spinlock_t *ptl;
676 
677         address = vma_address(page, vma);
678         if (address == -EFAULT)         /* out of vma range */
679                 return 0;
680         pte = page_check_address(page, vma->vm_mm, address, &ptl, 1);
681         if (!pte)                       /* the page is not in this mm */
682                 return 0;
683         pte_unmap_unlock(pte, ptl);
684 
685         return 1;
686 }
687 
688 /*
689  * Subfunctions of page_referenced: page_referenced_one called
690  * repeatedly from either page_referenced_anon or page_referenced_file.
691  */
692 int page_referenced_one(struct page *page, struct vm_area_struct *vma,
693                         unsigned long address, unsigned int *mapcount,
694                         unsigned long *vm_flags)
695 {
696         struct mm_struct *mm = vma->vm_mm;
697         int referenced = 0;
698 
699         if (unlikely(PageTransHuge(page))) {
700                 pmd_t *pmd;
701 
702                 spin_lock(&mm->page_table_lock);
703                 /*
704                  * rmap might return false positives; we must filter
705                  * these out using page_check_address_pmd().
706                  */
707                 pmd = page_check_address_pmd(page, mm, address,
708                                              PAGE_CHECK_ADDRESS_PMD_FLAG);
709                 if (!pmd) {
710                         spin_unlock(&mm->page_table_lock);
711                         goto out;
712                 }
713 
714                 if (vma->vm_flags & VM_LOCKED) {
715                         spin_unlock(&mm->page_table_lock);
716                         *mapcount = 0;  /* break early from loop */
717                         *vm_flags |= VM_LOCKED;
718                         goto out;
719                 }
720 
721                 /* go ahead even if the pmd is pmd_trans_splitting() */
722                 if (pmdp_clear_flush_young_notify(vma, address, pmd))
723                         referenced++;
724                 spin_unlock(&mm->page_table_lock);
725         } else {
726                 pte_t *pte;
727                 spinlock_t *ptl;
728 
729                 /*
730                  * rmap might return false positives; we must filter
731                  * these out using page_check_address().
732                  */
733                 pte = page_check_address(page, mm, address, &ptl, 0);
734                 if (!pte)
735                         goto out;
736 
737                 if (vma->vm_flags & VM_LOCKED) {
738                         pte_unmap_unlock(pte, ptl);
739                         *mapcount = 0;  /* break early from loop */
740                         *vm_flags |= VM_LOCKED;
741                         goto out;
742                 }
743 
744                 if (ptep_clear_flush_young_notify(vma, address, pte)) {
745                         /*
746                          * Don't treat a reference through a sequentially read
747                          * mapping as such.  If the page has been used in
748                          * another mapping, we will catch it; if this other
749                          * mapping is already gone, the unmap path will have
750                          * set PG_referenced or activated the page.
751                          */
752                         if (likely(!VM_SequentialReadHint(vma)))
753                                 referenced++;
754                 }
755                 pte_unmap_unlock(pte, ptl);
756         }
757 
758         /* Pretend the page is referenced if the task has the
759            swap token and is in the middle of a page fault. */
760         if (mm != current->mm && has_swap_token(mm) &&
761                         rwsem_is_locked(&mm->mmap_sem))
762                 referenced++;
763 
764         (*mapcount)--;
765 
766         if (referenced)
767                 *vm_flags |= vma->vm_flags;
768 out:
769         return referenced;
770 }
771 
772 static int page_referenced_anon(struct page *page,
773                                 struct mem_cgroup *memcg,
774                                 unsigned long *vm_flags)
775 {
776         unsigned int mapcount;
777         struct anon_vma *anon_vma;
778         struct anon_vma_chain *avc;
779         int referenced = 0;
780 
781         anon_vma = page_lock_anon_vma(page);
782         if (!anon_vma)
783                 return referenced;
784 
785         mapcount = page_mapcount(page);
786         list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
787                 struct vm_area_struct *vma = avc->vma;
788                 unsigned long address = vma_address(page, vma);
789                 if (address == -EFAULT)
790                         continue;
791                 /*
792                  * If we are reclaiming on behalf of a cgroup, skip
793                  * counting on behalf of references from different
794                  * cgroups
795                  */
796                 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
797                         continue;
798                 referenced += page_referenced_one(page, vma, address,
799                                                   &mapcount, vm_flags);
800                 if (!mapcount)
801                         break;
802         }
803 
804         page_unlock_anon_vma(anon_vma);
805         return referenced;
806 }
807 
808 /**
809  * page_referenced_file - referenced check for object-based rmap
810  * @page: the page we're checking references on.
811  * @memcg: target memory control group
812  * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
813  *
814  * For an object-based mapped page, find all the places it is mapped and
815  * check/clear the referenced flag.  This is done by following the page->mapping
816  * pointer, then walking the chain of vmas it holds.  It returns the number
817  * of references it found.
818  *
819  * This function is only called from page_referenced for object-based pages.
820  */
821 static int page_referenced_file(struct page *page,
822                                 struct mem_cgroup *memcg,
823                                 unsigned long *vm_flags)
824 {
825         unsigned int mapcount;
826         struct address_space *mapping = page->mapping;
827         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
828         struct vm_area_struct *vma;
829         struct prio_tree_iter iter;
830         int referenced = 0;
831 
832         /*
833          * The caller's checks on page->mapping and !PageAnon have made
834          * sure that this is a file page: the check for page->mapping
835          * excludes the case just before it gets set on an anon page.
836          */
837         BUG_ON(PageAnon(page));
838 
839         /*
840          * The page lock not only makes sure that page->mapping cannot
841          * suddenly be NULLified by truncation, it makes sure that the
842          * structure at mapping cannot be freed and reused yet,
843          * so we can safely take mapping->i_mmap_mutex.
844          */
845         BUG_ON(!PageLocked(page));
846 
847         mutex_lock(&mapping->i_mmap_mutex);
848 
849         /*
850          * i_mmap_mutex does not stabilize mapcount at all, but mapcount
851          * is more likely to be accurate if we note it after spinning.
852          */
853         mapcount = page_mapcount(page);
854 
855         vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
856                 unsigned long address = vma_address(page, vma);
857                 if (address == -EFAULT)
858                         continue;
859                 /*
860                  * If we are reclaiming on behalf of a cgroup, skip
861                  * counting on behalf of references from different
862                  * cgroups
863                  */
864                 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
865                         continue;
866                 referenced += page_referenced_one(page, vma, address,
867                                                   &mapcount, vm_flags);
868                 if (!mapcount)
869                         break;
870         }
871 
872         mutex_unlock(&mapping->i_mmap_mutex);
873         return referenced;
874 }
875 
876 /**
877  * page_referenced - test if the page was referenced
878  * @page: the page to test
879  * @is_locked: caller holds lock on the page
880  * @memcg: target memory cgroup
881  * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
882  *
883  * Quick test_and_clear_referenced for all mappings to a page,
884  * returns the number of ptes which referenced the page.
885  */
886 int page_referenced(struct page *page,
887                     int is_locked,
888                     struct mem_cgroup *memcg,
889                     unsigned long *vm_flags)
890 {
891         int referenced = 0;
892         int we_locked = 0;
893 
894         *vm_flags = 0;
895         if (page_mapped(page) && page_rmapping(page)) {
896                 if (!is_locked && (!PageAnon(page) || PageKsm(page))) {
897                         we_locked = trylock_page(page);
898                         if (!we_locked) {
899                                 referenced++;
900                                 goto out;
901                         }
902                 }
903                 if (unlikely(PageKsm(page)))
904                         referenced += page_referenced_ksm(page, memcg,
905                                                                 vm_flags);
906                 else if (PageAnon(page))
907                         referenced += page_referenced_anon(page, memcg,
908                                                                 vm_flags);
909                 else if (page->mapping)
910                         referenced += page_referenced_file(page, memcg,
911                                                                 vm_flags);
912                 if (we_locked)
913                         unlock_page(page);
914 
915                 if (page_test_and_clear_young(page_to_pfn(page)))
916                         referenced++;
917         }
918 out:
919         return referenced;
920 }
921 
922 static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
923                             unsigned long address)
924 {
925         struct mm_struct *mm = vma->vm_mm;
926         pte_t *pte;
927         spinlock_t *ptl;
928         int ret = 0;
929 
930         pte = page_check_address(page, mm, address, &ptl, 1);
931         if (!pte)
932                 goto out;
933 
934         if (pte_dirty(*pte) || pte_write(*pte)) {
935                 pte_t entry;
936 
937                 flush_cache_page(vma, address, pte_pfn(*pte));
938                 entry = ptep_clear_flush_notify(vma, address, pte);
939                 entry = pte_wrprotect(entry);
940                 entry = pte_mkclean(entry);
941                 set_pte_at(mm, address, pte, entry);
942                 ret = 1;
943         }
944 
945         pte_unmap_unlock(pte, ptl);
946 out:
947         return ret;
948 }
949 
950 static int page_mkclean_file(struct address_space *mapping, struct page *page)
951 {
952         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
953         struct vm_area_struct *vma;
954         struct prio_tree_iter iter;
955         int ret = 0;
956 
957         BUG_ON(PageAnon(page));
958 
959         mutex_lock(&mapping->i_mmap_mutex);
960         vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
961                 if (vma->vm_flags & VM_SHARED) {
962                         unsigned long address = vma_address(page, vma);
963                         if (address == -EFAULT)
964                                 continue;
965                         ret += page_mkclean_one(page, vma, address);
966                 }
967         }
968         mutex_unlock(&mapping->i_mmap_mutex);
969         return ret;
970 }
971 
972 int page_mkclean(struct page *page)
973 {
974         int ret = 0;
975 
976         BUG_ON(!PageLocked(page));
977 
978         if (page_mapped(page)) {
979                 struct address_space *mapping = page_mapping(page);
980                 if (mapping) {
981                         ret = page_mkclean_file(mapping, page);
982                         if (page_test_and_clear_dirty(page_to_pfn(page), 1))
983                                 ret = 1;
984                 }
985         }
986 
987         return ret;
988 }
989 EXPORT_SYMBOL_GPL(page_mkclean);
990 
991 /**
992  * page_move_anon_rmap - move a page to our anon_vma
993  * @page:       the page to move to our anon_vma
994  * @vma:        the vma the page belongs to
995  * @address:    the user virtual address mapped
996  *
997  * When a page belongs exclusively to one process after a COW event,
998  * that page can be moved into the anon_vma that belongs to just that
999  * process, so the rmap code will not search the parent or sibling
1000  * processes.
1001  */
1002 void page_move_anon_rmap(struct page *page,
1003         struct vm_area_struct *vma, unsigned long address)
1004 {
1005         struct anon_vma *anon_vma = vma->anon_vma;
1006 
1007         VM_BUG_ON(!PageLocked(page));
1008         VM_BUG_ON(!anon_vma);
1009         VM_BUG_ON(page->index != linear_page_index(vma, address));
1010 
1011         anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1012         page->mapping = (struct address_space *) anon_vma;
1013 }
1014 
1015 /**
1016  * __page_set_anon_rmap - set up new anonymous rmap
1017  * @page:       Page to add to rmap     
1018  * @vma:        VM area to add page to.
1019  * @address:    User virtual address of the mapping     
1020  * @exclusive:  the page is exclusively owned by the current process
1021  */
1022 static void __page_set_anon_rmap(struct page *page,
1023         struct vm_area_struct *vma, unsigned long address, int exclusive)
1024 {
1025         struct anon_vma *anon_vma = vma->anon_vma;
1026 
1027         BUG_ON(!anon_vma);
1028 
1029         if (PageAnon(page))
1030                 return;
1031 
1032         /*
1033          * If the page isn't exclusively mapped into this vma,
1034          * we must use the _oldest_ possible anon_vma for the
1035          * page mapping!
1036          */
1037         if (!exclusive)
1038                 anon_vma = anon_vma->root;
1039 
1040         anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1041         page->mapping = (struct address_space *) anon_vma;
1042         page->index = linear_page_index(vma, address);
1043 }
1044 
1045 /**
1046  * __page_check_anon_rmap - sanity check anonymous rmap addition
1047  * @page:       the page to add the mapping to
1048  * @vma:        the vm area in which the mapping is added
1049  * @address:    the user virtual address mapped
1050  */
1051 static void __page_check_anon_rmap(struct page *page,
1052         struct vm_area_struct *vma, unsigned long address)
1053 {
1054 #ifdef CONFIG_DEBUG_VM
1055         /*
1056          * The page's anon-rmap details (mapping and index) are guaranteed to
1057          * be set up correctly at this point.
1058          *
1059          * We have exclusion against page_add_anon_rmap because the caller
1060          * always holds the page locked, except if called from page_dup_rmap,
1061          * in which case the page is already known to be setup.
1062          *
1063          * We have exclusion against page_add_new_anon_rmap because those pages
1064          * are initially only visible via the pagetables, and the pte is locked
1065          * over the call to page_add_new_anon_rmap.
1066          */
1067         BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root);
1068         BUG_ON(page->index != linear_page_index(vma, address));
1069 #endif
1070 }
1071 
1072 /**
1073  * page_add_anon_rmap - add pte mapping to an anonymous page
1074  * @page:       the page to add the mapping to
1075  * @vma:        the vm area in which the mapping is added
1076  * @address:    the user virtual address mapped
1077  *
1078  * The caller needs to hold the pte lock, and the page must be locked in
1079  * the anon_vma case: to serialize mapping,index checking after setting,
1080  * and to ensure that PageAnon is not being upgraded racily to PageKsm
1081  * (but PageKsm is never downgraded to PageAnon).
1082  */
1083 void page_add_anon_rmap(struct page *page,
1084         struct vm_area_struct *vma, unsigned long address)
1085 {
1086         do_page_add_anon_rmap(page, vma, address, 0);
1087 }
1088 
1089 /*
1090  * Special version of the above for do_swap_page, which often runs
1091  * into pages that are exclusively owned by the current process.
1092  * Everybody else should continue to use page_add_anon_rmap above.
1093  */
1094 void do_page_add_anon_rmap(struct page *page,
1095         struct vm_area_struct *vma, unsigned long address, int exclusive)
1096 {
1097         int first = atomic_inc_and_test(&page->_mapcount);
1098         if (first) {
1099                 if (!PageTransHuge(page))
1100                         __inc_zone_page_state(page, NR_ANON_PAGES);
1101                 else
1102                         __inc_zone_page_state(page,
1103                                               NR_ANON_TRANSPARENT_HUGEPAGES);
1104         }
1105         if (unlikely(PageKsm(page)))
1106                 return;
1107 
1108         VM_BUG_ON(!PageLocked(page));
1109         /* address might be in next vma when migration races vma_adjust */
1110         if (first)
1111                 __page_set_anon_rmap(page, vma, address, exclusive);
1112         else
1113                 __page_check_anon_rmap(page, vma, address);
1114 }
1115 
1116 /**
1117  * page_add_new_anon_rmap - add pte mapping to a new anonymous page
1118  * @page:       the page to add the mapping to
1119  * @vma:        the vm area in which the mapping is added
1120  * @address:    the user virtual address mapped
1121  *
1122  * Same as page_add_anon_rmap but must only be called on *new* pages.
1123  * This means the inc-and-test can be bypassed.
1124  * Page does not have to be locked.
1125  */
1126 void page_add_new_anon_rmap(struct page *page,
1127         struct vm_area_struct *vma, unsigned long address)
1128 {
1129         VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
1130         SetPageSwapBacked(page);
1131         atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
1132         if (!PageTransHuge(page))
1133                 __inc_zone_page_state(page, NR_ANON_PAGES);
1134         else
1135                 __inc_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
1136         __page_set_anon_rmap(page, vma, address, 1);
1137         if (page_evictable(page, vma))
1138                 lru_cache_add_lru(page, LRU_ACTIVE_ANON);
1139         else
1140                 add_page_to_unevictable_list(page);
1141 }
1142 
1143 /**
1144  * page_add_file_rmap - add pte mapping to a file page
1145  * @page: the page to add the mapping to
1146  *
1147  * The caller needs to hold the pte lock.
1148  */
1149 void page_add_file_rmap(struct page *page)
1150 {
1151         bool locked;
1152         unsigned long flags;
1153 
1154         mem_cgroup_begin_update_page_stat(page, &locked, &flags);
1155         if (atomic_inc_and_test(&page->_mapcount)) {
1156                 __inc_zone_page_state(page, NR_FILE_MAPPED);
1157                 mem_cgroup_inc_page_stat(page, MEMCG_NR_FILE_MAPPED);
1158         }
1159         mem_cgroup_end_update_page_stat(page, &locked, &flags);
1160 }
1161 
1162 /**
1163  * page_remove_rmap - take down pte mapping from a page
1164  * @page: page to remove mapping from
1165  *
1166  * The caller needs to hold the pte lock.
1167  */
1168 void page_remove_rmap(struct page *page)
1169 {
1170         bool anon = PageAnon(page);
1171         bool locked;
1172         unsigned long flags;
1173 
1174         /*
1175          * The anon case has no mem_cgroup page_stat to update; but may
1176          * uncharge_page() below, where the lock ordering can deadlock if
1177          * we hold the lock against page_stat move: so avoid it on anon.
1178          */
1179         if (!anon)
1180                 mem_cgroup_begin_update_page_stat(page, &locked, &flags);
1181 
1182         /* page still mapped by someone else? */
1183         if (!atomic_add_negative(-1, &page->_mapcount))
1184                 goto out;
1185 
1186         /*
1187          * Now that the last pte has gone, s390 must transfer dirty
1188          * flag from storage key to struct page.  We can usually skip
1189          * this if the page is anon, so about to be freed; but perhaps
1190          * not if it's in swapcache - there might be another pte slot
1191          * containing the swap entry, but page not yet written to swap.
1192          */
1193         if ((!anon || PageSwapCache(page)) &&
1194             page_test_and_clear_dirty(page_to_pfn(page), 1))
1195                 set_page_dirty(page);
1196         /*
1197          * Hugepages are not counted in NR_ANON_PAGES nor NR_FILE_MAPPED
1198          * and not charged by memcg for now.
1199          */
1200         if (unlikely(PageHuge(page)))
1201                 goto out;
1202         if (anon) {
1203                 mem_cgroup_uncharge_page(page);
1204                 if (!PageTransHuge(page))
1205                         __dec_zone_page_state(page, NR_ANON_PAGES);
1206                 else
1207                         __dec_zone_page_state(page,
1208                                               NR_ANON_TRANSPARENT_HUGEPAGES);
1209         } else {
1210                 __dec_zone_page_state(page, NR_FILE_MAPPED);
1211                 mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
1212         }
1213         /*
1214          * It would be tidy to reset the PageAnon mapping here,
1215          * but that might overwrite a racing page_add_anon_rmap
1216          * which increments mapcount after us but sets mapping
1217          * before us: so leave the reset to free_hot_cold_page,
1218          * and remember that it's only reliable while mapped.
1219          * Leaving it set also helps swapoff to reinstate ptes
1220          * faster for those pages still in swapcache.
1221          */
1222 out:
1223         if (!anon)
1224                 mem_cgroup_end_update_page_stat(page, &locked, &flags);
1225 }
1226 
1227 /*
1228  * Subfunctions of try_to_unmap: try_to_unmap_one called
1229  * repeatedly from try_to_unmap_ksm, try_to_unmap_anon or try_to_unmap_file.
1230  */
1231 int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
1232                      unsigned long address, enum ttu_flags flags)
1233 {
1234         struct mm_struct *mm = vma->vm_mm;
1235         pte_t *pte;
1236         pte_t pteval;
1237         spinlock_t *ptl;
1238         int ret = SWAP_AGAIN;
1239 
1240         pte = page_check_address(page, mm, address, &ptl, 0);
1241         if (!pte)
1242                 goto out;
1243 
1244         /*
1245          * If the page is mlock()d, we cannot swap it out.
1246          * If it's recently referenced (perhaps page_referenced
1247          * skipped over this mm) then we should reactivate it.
1248          */
1249         if (!(flags & TTU_IGNORE_MLOCK)) {
1250                 if (vma->vm_flags & VM_LOCKED)
1251                         goto out_mlock;
1252 
1253                 if (TTU_ACTION(flags) == TTU_MUNLOCK)
1254                         goto out_unmap;
1255         }
1256         if (!(flags & TTU_IGNORE_ACCESS)) {
1257                 if (ptep_clear_flush_young_notify(vma, address, pte)) {
1258                         ret = SWAP_FAIL;
1259                         goto out_unmap;
1260                 }
1261         }
1262 
1263         /* Nuke the page table entry. */
1264         flush_cache_page(vma, address, page_to_pfn(page));
1265         pteval = ptep_clear_flush_notify(vma, address, pte);
1266 
1267         /* Move the dirty bit to the physical page now the pte is gone. */
1268         if (pte_dirty(pteval))
1269                 set_page_dirty(page);
1270 
1271         /* Update high watermark before we lower rss */
1272         update_hiwater_rss(mm);
1273 
1274         if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {
1275                 if (PageAnon(page))
1276                         dec_mm_counter(mm, MM_ANONPAGES);
1277                 else
1278                         dec_mm_counter(mm, MM_FILEPAGES);
1279                 set_pte_at(mm, address, pte,
1280                                 swp_entry_to_pte(make_hwpoison_entry(page)));
1281         } else if (PageAnon(page)) {
1282                 swp_entry_t entry = { .val = page_private(page) };
1283 
1284                 if (PageSwapCache(page)) {
1285                         /*
1286                          * Store the swap location in the pte.
1287                          * See handle_pte_fault() ...
1288                          */
1289                         if (swap_duplicate(entry) < 0) {
1290                                 set_pte_at(mm, address, pte, pteval);
1291                                 ret = SWAP_FAIL;
1292                                 goto out_unmap;
1293                         }
1294                         if (list_empty(&mm->mmlist)) {
1295                                 spin_lock(&mmlist_lock);
1296                                 if (list_empty(&mm->mmlist))
1297                                         list_add(&mm->mmlist, &init_mm.mmlist);
1298                                 spin_unlock(&mmlist_lock);
1299                         }
1300                         dec_mm_counter(mm, MM_ANONPAGES);
1301                         inc_mm_counter(mm, MM_SWAPENTS);
1302                 } else if (IS_ENABLED(CONFIG_MIGRATION)) {
1303                         /*
1304                          * Store the pfn of the page in a special migration
1305                          * pte. do_swap_page() will wait until the migration
1306                          * pte is removed and then restart fault handling.
1307                          */
1308                         BUG_ON(TTU_ACTION(flags) != TTU_MIGRATION);
1309                         entry = make_migration_entry(page, pte_write(pteval));
1310                 }
1311                 set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
1312                 BUG_ON(pte_file(*pte));
1313         } else if (IS_ENABLED(CONFIG_MIGRATION) &&
1314                    (TTU_ACTION(flags) == TTU_MIGRATION)) {
1315                 /* Establish migration entry for a file page */
1316                 swp_entry_t entry;
1317                 entry = make_migration_entry(page, pte_write(pteval));
1318                 set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
1319         } else
1320                 dec_mm_counter(mm, MM_FILEPAGES);
1321 
1322         page_remove_rmap(page);
1323         page_cache_release(page);
1324 
1325 out_unmap:
1326         pte_unmap_unlock(pte, ptl);
1327 out:
1328         return ret;
1329 
1330 out_mlock:
1331         pte_unmap_unlock(pte, ptl);
1332 
1333 
1334         /*
1335          * We need mmap_sem locking, Otherwise VM_LOCKED check makes
1336          * unstable result and race. Plus, We can't wait here because
1337          * we now hold anon_vma->mutex or mapping->i_mmap_mutex.
1338          * if trylock failed, the page remain in evictable lru and later
1339          * vmscan could retry to move the page to unevictable lru if the
1340          * page is actually mlocked.
1341          */
1342         if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
1343                 if (vma->vm_flags & VM_LOCKED) {
1344                         mlock_vma_page(page);
1345                         ret = SWAP_MLOCK;
1346                 }
1347                 up_read(&vma->vm_mm->mmap_sem);
1348         }
1349         return ret;
1350 }
1351 
1352 /*
1353  * objrmap doesn't work for nonlinear VMAs because the assumption that
1354  * offset-into-file correlates with offset-into-virtual-addresses does not hold.
1355  * Consequently, given a particular page and its ->index, we cannot locate the
1356  * ptes which are mapping that page without an exhaustive linear search.
1357  *
1358  * So what this code does is a mini "virtual scan" of each nonlinear VMA which
1359  * maps the file to which the target page belongs.  The ->vm_private_data field
1360  * holds the current cursor into that scan.  Successive searches will circulate
1361  * around the vma's virtual address space.
1362  *
1363  * So as more replacement pressure is applied to the pages in a nonlinear VMA,
1364  * more scanning pressure is placed against them as well.   Eventually pages
1365  * will become fully unmapped and are eligible for eviction.
1366  *
1367  * For very sparsely populated VMAs this is a little inefficient - chances are
1368  * there there won't be many ptes located within the scan cluster.  In this case
1369  * maybe we could scan further - to the end of the pte page, perhaps.
1370  *
1371  * Mlocked pages:  check VM_LOCKED under mmap_sem held for read, if we can
1372  * acquire it without blocking.  If vma locked, mlock the pages in the cluster,
1373  * rather than unmapping them.  If we encounter the "check_page" that vmscan is
1374  * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN.
1375  */
1376 #define CLUSTER_SIZE    min(32*PAGE_SIZE, PMD_SIZE)
1377 #define CLUSTER_MASK    (~(CLUSTER_SIZE - 1))
1378 
1379 static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
1380                 struct vm_area_struct *vma, struct page *check_page)
1381 {
1382         struct mm_struct *mm = vma->vm_mm;
1383         pgd_t *pgd;
1384         pud_t *pud;
1385         pmd_t *pmd;
1386         pte_t *pte;
1387         pte_t pteval;
1388         spinlock_t *ptl;
1389         struct page *page;
1390         unsigned long address;
1391         unsigned long end;
1392         int ret = SWAP_AGAIN;
1393         int locked_vma = 0;
1394 
1395         address = (vma->vm_start + cursor) & CLUSTER_MASK;
1396         end = address + CLUSTER_SIZE;
1397         if (address < vma->vm_start)
1398                 address = vma->vm_start;
1399         if (end > vma->vm_end)
1400                 end = vma->vm_end;
1401 
1402         pgd = pgd_offset(mm, address);
1403         if (!pgd_present(*pgd))
1404                 return ret;
1405 
1406         pud = pud_offset(pgd, address);
1407         if (!pud_present(*pud))
1408                 return ret;
1409 
1410         pmd = pmd_offset(pud, address);
1411         if (!pmd_present(*pmd))
1412                 return ret;
1413 
1414         /*
1415          * If we can acquire the mmap_sem for read, and vma is VM_LOCKED,
1416          * keep the sem while scanning the cluster for mlocking pages.
1417          */
1418         if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
1419                 locked_vma = (vma->vm_flags & VM_LOCKED);
1420                 if (!locked_vma)
1421                         up_read(&vma->vm_mm->mmap_sem); /* don't need it */
1422         }
1423 
1424         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1425 
1426         /* Update high watermark before we lower rss */
1427         update_hiwater_rss(mm);
1428 
1429         for (; address < end; pte++, address += PAGE_SIZE) {
1430                 if (!pte_present(*pte))
1431                         continue;
1432                 page = vm_normal_page(vma, address, *pte);
1433                 BUG_ON(!page || PageAnon(page));
1434 
1435                 if (locked_vma) {
1436                         mlock_vma_page(page);   /* no-op if already mlocked */
1437                         if (page == check_page)
1438                                 ret = SWAP_MLOCK;
1439                         continue;       /* don't unmap */
1440                 }
1441 
1442                 if (ptep_clear_flush_young_notify(vma, address, pte))
1443                         continue;
1444 
1445                 /* Nuke the page table entry. */
1446                 flush_cache_page(vma, address, pte_pfn(*pte));
1447                 pteval = ptep_clear_flush_notify(vma, address, pte);
1448 
1449                 /* If nonlinear, store the file page offset in the pte. */
1450                 if (page->index != linear_page_index(vma, address))
1451                         set_pte_at(mm, address, pte, pgoff_to_pte(page->index));
1452 
1453                 /* Move the dirty bit to the physical page now the pte is gone. */
1454                 if (pte_dirty(pteval))
1455                         set_page_dirty(page);
1456 
1457                 page_remove_rmap(page);
1458                 page_cache_release(page);
1459                 dec_mm_counter(mm, MM_FILEPAGES);
1460                 (*mapcount)--;
1461         }
1462         pte_unmap_unlock(pte - 1, ptl);
1463         if (locked_vma)
1464                 up_read(&vma->vm_mm->mmap_sem);
1465         return ret;
1466 }
1467 
1468 bool is_vma_temporary_stack(struct vm_area_struct *vma)
1469 {
1470         int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);
1471 
1472         if (!maybe_stack)
1473                 return false;
1474 
1475         if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
1476                                                 VM_STACK_INCOMPLETE_SETUP)
1477                 return true;
1478 
1479         return false;
1480 }
1481 
1482 /**
1483  * try_to_unmap_anon - unmap or unlock anonymous page using the object-based
1484  * rmap method
1485  * @page: the page to unmap/unlock
1486  * @flags: action and flags
1487  *
1488  * Find all the mappings of a page using the mapping pointer and the vma chains
1489  * contained in the anon_vma struct it points to.
1490  *
1491  * This function is only called from try_to_unmap/try_to_munlock for
1492  * anonymous pages.
1493  * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
1494  * where the page was found will be held for write.  So, we won't recheck
1495  * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
1496  * 'LOCKED.
1497  */
1498 static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
1499 {
1500         struct anon_vma *anon_vma;
1501         struct anon_vma_chain *avc;
1502         int ret = SWAP_AGAIN;
1503 
1504         anon_vma = page_lock_anon_vma(page);
1505         if (!anon_vma)
1506                 return ret;
1507 
1508         list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
1509                 struct vm_area_struct *vma = avc->vma;
1510                 unsigned long address;
1511 
1512                 /*
1513                  * During exec, a temporary VMA is setup and later moved.
1514                  * The VMA is moved under the anon_vma lock but not the
1515                  * page tables leading to a race where migration cannot
1516                  * find the migration ptes. Rather than increasing the
1517                  * locking requirements of exec(), migration skips
1518                  * temporary VMAs until after exec() completes.
1519                  */
1520                 if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) &&
1521                                 is_vma_temporary_stack(vma))
1522                         continue;
1523 
1524                 address = vma_address(page, vma);
1525                 if (address == -EFAULT)
1526                         continue;
1527                 ret = try_to_unmap_one(page, vma, address, flags);
1528                 if (ret != SWAP_AGAIN || !page_mapped(page))
1529                         break;
1530         }
1531 
1532         page_unlock_anon_vma(anon_vma);
1533         return ret;
1534 }
1535 
1536 /**
1537  * try_to_unmap_file - unmap/unlock file page using the object-based rmap method
1538  * @page: the page to unmap/unlock
1539  * @flags: action and flags
1540  *
1541  * Find all the mappings of a page using the mapping pointer and the vma chains
1542  * contained in the address_space struct it points to.
1543  *
1544  * This function is only called from try_to_unmap/try_to_munlock for
1545  * object-based pages.
1546  * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
1547  * where the page was found will be held for write.  So, we won't recheck
1548  * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
1549  * 'LOCKED.
1550  */
1551 static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
1552 {
1553         struct address_space *mapping = page->mapping;
1554         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1555         struct vm_area_struct *vma;
1556         struct prio_tree_iter iter;
1557         int ret = SWAP_AGAIN;
1558         unsigned long cursor;
1559         unsigned long max_nl_cursor = 0;
1560         unsigned long max_nl_size = 0;
1561         unsigned int mapcount;
1562 
1563         mutex_lock(&mapping->i_mmap_mutex);
1564         vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
1565                 unsigned long address = vma_address(page, vma);
1566                 if (address == -EFAULT)
1567                         continue;
1568                 ret = try_to_unmap_one(page, vma, address, flags);
1569                 if (ret != SWAP_AGAIN || !page_mapped(page))
1570                         goto out;
1571         }
1572 
1573         if (list_empty(&mapping->i_mmap_nonlinear))
1574                 goto out;
1575 
1576         /*
1577          * We don't bother to try to find the munlocked page in nonlinears.
1578          * It's costly. Instead, later, page reclaim logic may call
1579          * try_to_unmap(TTU_MUNLOCK) and recover PG_mlocked lazily.
1580          */
1581         if (TTU_ACTION(flags) == TTU_MUNLOCK)
1582                 goto out;
1583 
1584         list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
1585                                                 shared.vm_set.list) {
1586                 cursor = (unsigned long) vma->vm_private_data;
1587                 if (cursor > max_nl_cursor)
1588                         max_nl_cursor = cursor;
1589                 cursor = vma->vm_end - vma->vm_start;
1590                 if (cursor > max_nl_size)
1591                         max_nl_size = cursor;
1592         }
1593 
1594         if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */
1595                 ret = SWAP_FAIL;
1596                 goto out;
1597         }
1598 
1599         /*
1600          * We don't try to search for this page in the nonlinear vmas,
1601          * and page_referenced wouldn't have found it anyway.  Instead
1602          * just walk the nonlinear vmas trying to age and unmap some.
1603          * The mapcount of the page we came in with is irrelevant,
1604          * but even so use it as a guide to how hard we should try?
1605          */
1606         mapcount = page_mapcount(page);
1607         if (!mapcount)
1608                 goto out;
1609         cond_resched();
1610 
1611         max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
1612         if (max_nl_cursor == 0)
1613                 max_nl_cursor = CLUSTER_SIZE;
1614 
1615         do {
1616                 list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
1617                                                 shared.vm_set.list) {
1618                         cursor = (unsigned long) vma->vm_private_data;
1619                         while ( cursor < max_nl_cursor &&
1620                                 cursor < vma->vm_end - vma->vm_start) {
1621                                 if (try_to_unmap_cluster(cursor, &mapcount,
1622                                                 vma, page) == SWAP_MLOCK)
1623                                         ret = SWAP_MLOCK;
1624                                 cursor += CLUSTER_SIZE;
1625                                 vma->vm_private_data = (void *) cursor;
1626                                 if ((int)mapcount <= 0)
1627                                         goto out;
1628                         }
1629                         vma->vm_private_data = (void *) max_nl_cursor;
1630                 }
1631                 cond_resched();
1632                 max_nl_cursor += CLUSTER_SIZE;
1633         } while (max_nl_cursor <= max_nl_size);
1634 
1635         /*
1636          * Don't loop forever (perhaps all the remaining pages are
1637          * in locked vmas).  Reset cursor on all unreserved nonlinear
1638          * vmas, now forgetting on which ones it had fallen behind.
1639          */
1640         list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
1641                 vma->vm_private_data = NULL;
1642 out:
1643         mutex_unlock(&mapping->i_mmap_mutex);
1644         return ret;
1645 }
1646 
1647 /**
1648  * try_to_unmap - try to remove all page table mappings to a page
1649  * @page: the page to get unmapped
1650  * @flags: action and flags
1651  *
1652  * Tries to remove all the page table entries which are mapping this
1653  * page, used in the pageout path.  Caller must hold the page lock.
1654  * Return values are:
1655  *
1656  * SWAP_SUCCESS - we succeeded in removing all mappings
1657  * SWAP_AGAIN   - we missed a mapping, try again later
1658  * SWAP_FAIL    - the page is unswappable
1659  * SWAP_MLOCK   - page is mlocked.
1660  */
1661 int try_to_unmap(struct page *page, enum ttu_flags flags)
1662 {
1663         int ret;
1664 
1665         BUG_ON(!PageLocked(page));
1666         VM_BUG_ON(!PageHuge(page) && PageTransHuge(page));
1667 
1668         if (unlikely(PageKsm(page)))
1669                 ret = try_to_unmap_ksm(page, flags);
1670         else if (PageAnon(page))
1671                 ret = try_to_unmap_anon(page, flags);
1672         else
1673                 ret = try_to_unmap_file(page, flags);
1674         if (ret != SWAP_MLOCK && !page_mapped(page))
1675                 ret = SWAP_SUCCESS;
1676         return ret;
1677 }
1678 
1679 /**
1680  * try_to_munlock - try to munlock a page
1681  * @page: the page to be munlocked
1682  *
1683  * Called from munlock code.  Checks all of the VMAs mapping the page
1684  * to make sure nobody else has this page mlocked. The page will be
1685  * returned with PG_mlocked cleared if no other vmas have it mlocked.
1686  *
1687  * Return values are:
1688  *
1689  * SWAP_AGAIN   - no vma is holding page mlocked, or,
1690  * SWAP_AGAIN   - page mapped in mlocked vma -- couldn't acquire mmap sem
1691  * SWAP_FAIL    - page cannot be located at present
1692  * SWAP_MLOCK   - page is now mlocked.
1693  */
1694 int try_to_munlock(struct page *page)
1695 {
1696         VM_BUG_ON(!PageLocked(page) || PageLRU(page));
1697 
1698         if (unlikely(PageKsm(page)))
1699                 return try_to_unmap_ksm(page, TTU_MUNLOCK);
1700         else if (PageAnon(page))
1701                 return try_to_unmap_anon(page, TTU_MUNLOCK);
1702         else
1703                 return try_to_unmap_file(page, TTU_MUNLOCK);
1704 }
1705 
1706 void __put_anon_vma(struct anon_vma *anon_vma)
1707 {
1708         struct anon_vma *root = anon_vma->root;
1709 
1710         if (root != anon_vma && atomic_dec_and_test(&root->refcount))
1711                 anon_vma_free(root);
1712 
1713         anon_vma_free(anon_vma);
1714 }
1715 
1716 #ifdef CONFIG_MIGRATION
1717 /*
1718  * rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file():
1719  * Called by migrate.c to remove migration ptes, but might be used more later.
1720  */
1721 static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
1722                 struct vm_area_struct *, unsigned long, void *), void *arg)
1723 {
1724         struct anon_vma *anon_vma;
1725         struct anon_vma_chain *avc;
1726         int ret = SWAP_AGAIN;
1727 
1728         /*
1729          * Note: remove_migration_ptes() cannot use page_lock_anon_vma()
1730          * because that depends on page_mapped(); but not all its usages
1731          * are holding mmap_sem. Users without mmap_sem are required to
1732          * take a reference count to prevent the anon_vma disappearing
1733          */
1734         anon_vma = page_anon_vma(page);
1735         if (!anon_vma)
1736                 return ret;
1737         anon_vma_lock(anon_vma);
1738         list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
1739                 struct vm_area_struct *vma = avc->vma;
1740                 unsigned long address = vma_address(page, vma);
1741                 if (address == -EFAULT)
1742                         continue;
1743                 ret = rmap_one(page, vma, address, arg);
1744                 if (ret != SWAP_AGAIN)
1745                         break;
1746         }
1747         anon_vma_unlock(anon_vma);
1748         return ret;
1749 }
1750 
1751 static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *,
1752                 struct vm_area_struct *, unsigned long, void *), void *arg)
1753 {
1754         struct address_space *mapping = page->mapping;
1755         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1756         struct vm_area_struct *vma;
1757         struct prio_tree_iter iter;
1758         int ret = SWAP_AGAIN;
1759 
1760         if (!mapping)
1761                 return ret;
1762         mutex_lock(&mapping->i_mmap_mutex);
1763         vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
1764                 unsigned long address = vma_address(page, vma);
1765                 if (address == -EFAULT)
1766                         continue;
1767                 ret = rmap_one(page, vma, address, arg);
1768                 if (ret != SWAP_AGAIN)
1769                         break;
1770         }
1771         /*
1772          * No nonlinear handling: being always shared, nonlinear vmas
1773          * never contain migration ptes.  Decide what to do about this
1774          * limitation to linear when we need rmap_walk() on nonlinear.
1775          */
1776         mutex_unlock(&mapping->i_mmap_mutex);
1777         return ret;
1778 }
1779 
1780 int rmap_walk(struct page *page, int (*rmap_one)(struct page *,
1781                 struct vm_area_struct *, unsigned long, void *), void *arg)
1782 {
1783         VM_BUG_ON(!PageLocked(page));
1784 
1785         if (unlikely(PageKsm(page)))
1786                 return rmap_walk_ksm(page, rmap_one, arg);
1787         else if (PageAnon(page))
1788                 return rmap_walk_anon(page, rmap_one, arg);
1789         else
1790                 return rmap_walk_file(page, rmap_one, arg);
1791 }
1792 #endif /* CONFIG_MIGRATION */
1793 
1794 #ifdef CONFIG_HUGETLB_PAGE
1795 /*
1796  * The following three functions are for anonymous (private mapped) hugepages.
1797  * Unlike common anonymous pages, anonymous hugepages have no accounting code
1798  * and no lru code, because we handle hugepages differently from common pages.
1799  */
1800 static void __hugepage_set_anon_rmap(struct page *page,
1801         struct vm_area_struct *vma, unsigned long address, int exclusive)
1802 {
1803         struct anon_vma *anon_vma = vma->anon_vma;
1804 
1805         BUG_ON(!anon_vma);
1806 
1807         if (PageAnon(page))
1808                 return;
1809         if (!exclusive)
1810                 anon_vma = anon_vma->root;
1811 
1812         anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1813         page->mapping = (struct address_space *) anon_vma;
1814         page->index = linear_page_index(vma, address);
1815 }
1816 
1817 void hugepage_add_anon_rmap(struct page *page,
1818                             struct vm_area_struct *vma, unsigned long address)
1819 {
1820         struct anon_vma *anon_vma = vma->anon_vma;
1821         int first;
1822 
1823         BUG_ON(!PageLocked(page));
1824         BUG_ON(!anon_vma);
1825         /* address might be in next vma when migration races vma_adjust */
1826         first = atomic_inc_and_test(&page->_mapcount);
1827         if (first)
1828                 __hugepage_set_anon_rmap(page, vma, address, 0);
1829 }
1830 
1831 void hugepage_add_new_anon_rmap(struct page *page,
1832                         struct vm_area_struct *vma, unsigned long address)
1833 {
1834         BUG_ON(address < vma->vm_start || address >= vma->vm_end);
1835         atomic_set(&page->_mapcount, 0);
1836         __hugepage_set_anon_rmap(page, vma, address, 1);
1837 }
1838 #endif /* CONFIG_HUGETLB_PAGE */
1839 

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