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

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