xref: /openbmc/linux/mm/rmap.c (revision ae3473231e77a3f1909d48cd144cebe5e1d049b3)
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