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Linux/mm/rmap.c

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

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