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Root/mm/rmap.c

1	/*
2	* mm/rmap.c - physical to virtual reverse mappings
3	*
4	* Copyright 2001, Rik van Riel <riel@conectiva.com.br>
5	* Released under the General Public License (GPL).
6	*
7	* Simple, low overhead reverse mapping scheme.
8	* Please try to keep this thing as modular as possible.
9	*
10	* Provides methods for unmapping each kind of mapped page:
11	* the anon methods track anonymous pages, and
12	* the file methods track pages belonging to an inode.
13	*
14	* Original design by Rik van Riel <riel@conectiva.com.br> 2001
15	* File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004
16	* Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004
17	* Contributions by Hugh Dickins 2003, 2004
18	*/
19
20	/*
21	* Lock ordering in mm:
22	*
23	* inode->i_mutex (while writing or truncating, not reading or faulting)
24	* mm->mmap_sem
25	* page->flags PG_locked (lock_page)
26	* mapping->i_mmap_mutex
27	* anon_vma->mutex
28	* mm->page_table_lock or pte_lock
29	* zone->lru_lock (in mark_page_accessed, isolate_lru_page)
30	* swap_lock (in swap_duplicate, swap_info_get)
31	* mmlist_lock (in mmput, drain_mmlist and others)
32	* mapping->private_lock (in __set_page_dirty_buffers)
33	* inode->i_lock (in set_page_dirty's __mark_inode_dirty)
34	* bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
35	* sb_lock (within inode_lock in fs/fs-writeback.c)
36	* mapping->tree_lock (widely used, in set_page_dirty,
37	* in arch-dependent flush_dcache_mmap_lock,
38	* within bdi.wb->list_lock in __sync_single_inode)
39	*
40	* anon_vma->mutex,mapping->i_mutex (memory_failure, collect_procs_anon)
41	* ->tasklist_lock
42	* pte map lock
43	*/
44
45	#include <linux/mm.h>
46	#include <linux/pagemap.h>
47	#include <linux/swap.h>
48	#include <linux/swapops.h>
49	#include <linux/slab.h>
50	#include <linux/init.h>
51	#include <linux/ksm.h>
52	#include <linux/rmap.h>
53	#include <linux/rcupdate.h>
54	#include <linux/export.h>
55	#include <linux/memcontrol.h>
56	#include <linux/mmu_notifier.h>
57	#include <linux/migrate.h>
58	#include <linux/hugetlb.h>
59
60	#include <asm/tlbflush.h>
61
62	#include "internal.h"
63
64	static struct kmem_cache *anon_vma_cachep;
65	static struct kmem_cache *anon_vma_chain_cachep;
66
67	static inline struct anon_vma *anon_vma_alloc(void)
68	{
69	struct anon_vma *anon_vma;
70
71	anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
72	if (anon_vma) {
73	atomic_set(&anon_vma->refcount, 1);
74	/*
75	* Initialise the anon_vma root to point to itself. If called
76	* from fork, the root will be reset to the parents anon_vma.
77	*/
78	anon_vma->root = anon_vma;
79	}
80
81	return anon_vma;
82	}
83
84	static inline void anon_vma_free(struct anon_vma *anon_vma)
85	{
86	VM_BUG_ON(atomic_read(&anon_vma->refcount));
87
88	/*
89	* Synchronize against page_lock_anon_vma() such that
90	* we can safely hold the lock without the anon_vma getting
91	* freed.
92	*
93	* Relies on the full mb implied by the atomic_dec_and_test() from
94	* put_anon_vma() against the acquire barrier implied by
95	* mutex_trylock() from page_lock_anon_vma(). This orders:
96	*
97	* page_lock_anon_vma() VS put_anon_vma()
98	* mutex_trylock() atomic_dec_and_test()
99	* LOCK MB
100	* atomic_read() mutex_is_locked()
101	*
102	* LOCK should suffice since the actual taking of the lock must
103	* happen _before_ what follows.
104	*/
105	if (mutex_is_locked(&anon_vma->root->mutex)) {
106	anon_vma_lock(anon_vma);
107	anon_vma_unlock(anon_vma);
108	}
109
110	kmem_cache_free(anon_vma_cachep, anon_vma);
111	}
112
113	static inline struct anon_vma_chain *anon_vma_chain_alloc(gfp_t gfp)
114	{
115	return kmem_cache_alloc(anon_vma_chain_cachep, gfp);
116	}
117
118	static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
119	{
120	kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain);
121	}
122
123	static void anon_vma_chain_link(struct vm_area_struct *vma,
124	struct anon_vma_chain *avc,
125	struct anon_vma *anon_vma)
126	{
127	avc->vma = vma;
128	avc->anon_vma = anon_vma;
129	list_add(&avc->same_vma, &vma->anon_vma_chain);
130
131	/*
132	* It's critical to add new vmas to the tail of the anon_vma,
133	* see comment in huge_memory.c:__split_huge_page().
134	*/
135	list_add_tail(&avc->same_anon_vma, &anon_vma->head);
136	}
137
138	/**
139	* anon_vma_prepare - attach an anon_vma to a memory region
140	* @vma: the memory region in question
141	*
142	* This makes sure the memory mapping described by 'vma' has
143	* an 'anon_vma' attached to it, so that we can associate the
144	* anonymous pages mapped into it with that anon_vma.
145	*
146	* The common case will be that we already have one, but if
147	* not we either need to find an adjacent mapping that we
148	* can re-use the anon_vma from (very common when the only
149	* reason for splitting a vma has been mprotect()), or we
150	* allocate a new one.
151	*
152	* Anon-vma allocations are very subtle, because we may have
153	* optimistically looked up an anon_vma in page_lock_anon_vma()
154	* and that may actually touch the spinlock even in the newly
155	* allocated vma (it depends on RCU to make sure that the
156	* anon_vma isn't actually destroyed).
157	*
158	* As a result, we need to do proper anon_vma locking even
159	* for the new allocation. At the same time, we do not want
160	* to do any locking for the common case of already having
161	* an anon_vma.
162	*
163	* This must be called with the mmap_sem held for reading.
164	*/
165	int anon_vma_prepare(struct vm_area_struct *vma)
166	{
167	struct anon_vma *anon_vma = vma->anon_vma;
168	struct anon_vma_chain *avc;
169
170	might_sleep();
171	if (unlikely(!anon_vma)) {
172	struct mm_struct *mm = vma->vm_mm;
173	struct anon_vma *allocated;
174
175	avc = anon_vma_chain_alloc(GFP_KERNEL);
176	if (!avc)
177	goto out_enomem;
178
179	anon_vma = find_mergeable_anon_vma(vma);
180	allocated = NULL;
181	if (!anon_vma) {
182	anon_vma = anon_vma_alloc();
183	if (unlikely(!anon_vma))
184	goto out_enomem_free_avc;
185	allocated = anon_vma;
186	}
187
188	anon_vma_lock(anon_vma);
189	/* page_table_lock to protect against threads */
190	spin_lock(&mm->page_table_lock);
191	if (likely(!vma->anon_vma)) {
192	vma->anon_vma = anon_vma;
193	anon_vma_chain_link(vma, avc, anon_vma);
194	allocated = NULL;
195	avc = NULL;
196	}
197	spin_unlock(&mm->page_table_lock);
198	anon_vma_unlock(anon_vma);
199
200	if (unlikely(allocated))
201	put_anon_vma(allocated);
202	if (unlikely(avc))
203	anon_vma_chain_free(avc);
204	}
205	return 0;
206
207	out_enomem_free_avc:
208	anon_vma_chain_free(avc);
209	out_enomem:
210	return -ENOMEM;
211	}
212
213	/*
214	* This is a useful helper function for locking the anon_vma root as
215	* we traverse the vma->anon_vma_chain, looping over anon_vma's that
216	* have the same vma.
217	*
218	* Such anon_vma's should have the same root, so you'd expect to see
219	* just a single mutex_lock for the whole traversal.
220	*/
221	static inline struct anon_vma lock_anon_vma_root(struct anon_vma root, struct anon_vma *anon_vma)
222	{
223	struct anon_vma *new_root = anon_vma->root;
224	if (new_root != root) {
225	if (WARN_ON_ONCE(root))
226	mutex_unlock(&root->mutex);
227	root = new_root;
228	mutex_lock(&root->mutex);
229	}
230	return root;
231	}
232
233	static inline void unlock_anon_vma_root(struct anon_vma *root)
234	{
235	if (root)
236	mutex_unlock(&root->mutex);
237	}
238
239	/*
240	* Attach the anon_vmas from src to dst.
241	* Returns 0 on success, -ENOMEM on failure.
242	*/
243	int anon_vma_clone(struct vm_area_struct dst, struct vm_area_struct src)
244	{
245	struct anon_vma_chain avc, pavc;
246	struct anon_vma *root = NULL;
247
248	list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
249	struct anon_vma *anon_vma;
250
251	avc = anon_vma_chain_alloc(GFP_NOWAIT \| __GFP_NOWARN);
252	if (unlikely(!avc)) {
253	unlock_anon_vma_root(root);
254	root = NULL;
255	avc = anon_vma_chain_alloc(GFP_KERNEL);
256	if (!avc)
257	goto enomem_failure;
258	}
259	anon_vma = pavc->anon_vma;
260	root = lock_anon_vma_root(root, anon_vma);
261	anon_vma_chain_link(dst, avc, anon_vma);
262	}
263	unlock_anon_vma_root(root);
264	return 0;
265
266	enomem_failure:
267	unlink_anon_vmas(dst);
268	return -ENOMEM;
269	}
270
271	/*
272	* Some rmap walk that needs to find all ptes/hugepmds without false
273	* negatives (like migrate and split_huge_page) running concurrent
274	* with operations that copy or move pagetables (like mremap() and
275	* fork()) to be safe. They depend on the anon_vma "same_anon_vma"
276	* list to be in a certain order: the dst_vma must be placed after the
277	* src_vma in the list. This is always guaranteed by fork() but
278	* mremap() needs to call this function to enforce it in case the
279	* dst_vma isn't newly allocated and chained with the anon_vma_clone()
280	* function but just an extension of a pre-existing vma through
281	* vma_merge.
282	*
283	* NOTE: the same_anon_vma list can still be changed by other
284	* processes while mremap runs because mremap doesn't hold the
285	* anon_vma mutex to prevent modifications to the list while it
286	* runs. All we need to enforce is that the relative order of this
287	* process vmas isn't changing (we don't care about other vmas
288	* order). Each vma corresponds to an anon_vma_chain structure so
289	* there's no risk that other processes calling anon_vma_moveto_tail()
290	* and changing the same_anon_vma list under mremap() will screw with
291	* the relative order of this process vmas in the list, because we
292	* they can't alter the order of any vma that belongs to this
293	* process. And there can't be another anon_vma_moveto_tail() running
294	* concurrently with mremap() coming from this process because we hold
295	* the mmap_sem for the whole mremap(). fork() ordering dependency
296	* also shouldn't be affected because fork() only cares that the
297	* parent vmas are placed in the list before the child vmas and
298	* anon_vma_moveto_tail() won't reorder vmas from either the fork()
299	* parent or child.
300	*/
301	void anon_vma_moveto_tail(struct vm_area_struct *dst)
302	{
303	struct anon_vma_chain *pavc;
304	struct anon_vma *root = NULL;
305
306	list_for_each_entry_reverse(pavc, &dst->anon_vma_chain, same_vma) {
307	struct anon_vma *anon_vma = pavc->anon_vma;
308	VM_BUG_ON(pavc->vma != dst);
309	root = lock_anon_vma_root(root, anon_vma);
310	list_del(&pavc->same_anon_vma);
311	list_add_tail(&pavc->same_anon_vma, &anon_vma->head);
312	}
313	unlock_anon_vma_root(root);
314	}
315
316	/*
317	* Attach vma to its own anon_vma, as well as to the anon_vmas that
318	* the corresponding VMA in the parent process is attached to.
319	* Returns 0 on success, non-zero on failure.
320	*/
321	int anon_vma_fork(struct vm_area_struct vma, struct vm_area_struct pvma)
322	{
323	struct anon_vma_chain *avc;
324	struct anon_vma *anon_vma;
325
326	/* Don't bother if the parent process has no anon_vma here. */
327	if (!pvma->anon_vma)
328	return 0;
329
330	/*
331	* First, attach the new VMA to the parent VMA's anon_vmas,
332	* so rmap can find non-COWed pages in child processes.
333	*/
334	if (anon_vma_clone(vma, pvma))
335	return -ENOMEM;
336
337	/* Then add our own anon_vma. */
338	anon_vma = anon_vma_alloc();
339	if (!anon_vma)
340	goto out_error;
341	avc = anon_vma_chain_alloc(GFP_KERNEL);
342	if (!avc)
343	goto out_error_free_anon_vma;
344
345	/*
346	* The root anon_vma's spinlock is the lock actually used when we
347	* lock any of the anon_vmas in this anon_vma tree.
348	*/
349	anon_vma->root = pvma->anon_vma->root;
350	/*
351	* With refcounts, an anon_vma can stay around longer than the
352	* process it belongs to. The root anon_vma needs to be pinned until
353	* this anon_vma is freed, because the lock lives in the root.
354	*/
355	get_anon_vma(anon_vma->root);
356	/* Mark this anon_vma as the one where our new (COWed) pages go. */
357	vma->anon_vma = anon_vma;
358	anon_vma_lock(anon_vma);
359	anon_vma_chain_link(vma, avc, anon_vma);
360	anon_vma_unlock(anon_vma);
361
362	return 0;
363
364	out_error_free_anon_vma:
365	put_anon_vma(anon_vma);
366	out_error:
367	unlink_anon_vmas(vma);
368	return -ENOMEM;
369	}
370
371	void unlink_anon_vmas(struct vm_area_struct *vma)
372	{
373	struct anon_vma_chain avc, next;
374	struct anon_vma *root = NULL;
375
376	/*
377	* Unlink each anon_vma chained to the VMA. This list is ordered
378	* from newest to oldest, ensuring the root anon_vma gets freed last.
379	*/
380	list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
381	struct anon_vma *anon_vma = avc->anon_vma;
382
383	root = lock_anon_vma_root(root, anon_vma);
384	list_del(&avc->same_anon_vma);
385
386	/*
387	* Leave empty anon_vmas on the list - we'll need
388	* to free them outside the lock.
389	*/
390	if (list_empty(&anon_vma->head))
391	continue;
392
393	list_del(&avc->same_vma);
394	anon_vma_chain_free(avc);
395	}
396	unlock_anon_vma_root(root);
397
398	/*
399	* Iterate the list once more, it now only contains empty and unlinked
400	* anon_vmas, destroy them. Could not do before due to __put_anon_vma()
401	* needing to acquire the anon_vma->root->mutex.
402	*/
403	list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
404	struct anon_vma *anon_vma = avc->anon_vma;
405
406	put_anon_vma(anon_vma);
407
408	list_del(&avc->same_vma);
409	anon_vma_chain_free(avc);
410	}
411	}
412
413	static void anon_vma_ctor(void *data)
414	{
415	struct anon_vma *anon_vma = data;
416
417	mutex_init(&anon_vma->mutex);
418	atomic_set(&anon_vma->refcount, 0);
419	INIT_LIST_HEAD(&anon_vma->head);
420	}
421
422	void __init anon_vma_init(void)
423	{
424	anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
425	0, SLAB_DESTROY_BY_RCU\|SLAB_PANIC, anon_vma_ctor);
426	anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC);
427	}
428
429	/*
430	* Getting a lock on a stable anon_vma from a page off the LRU is tricky!
431	*
432	* Since there is no serialization what so ever against page_remove_rmap()
433	* the best this function can do is return a locked anon_vma that might
434	* have been relevant to this page.
435	*
436	* The page might have been remapped to a different anon_vma or the anon_vma
437	* returned may already be freed (and even reused).
438	*
439	* In case it was remapped to a different anon_vma, the new anon_vma will be a
440	* child of the old anon_vma, and the anon_vma lifetime rules will therefore
441	* ensure that any anon_vma obtained from the page will still be valid for as
442	* long as we observe page_mapped() [ hence all those page_mapped() tests ].
443	*
444	* All users of this function must be very careful when walking the anon_vma
445	* chain and verify that the page in question is indeed mapped in it
446	* [ something equivalent to page_mapped_in_vma() ].
447	*
448	* Since anon_vma's slab is DESTROY_BY_RCU and we know from page_remove_rmap()
449	* that the anon_vma pointer from page->mapping is valid if there is a
450	* mapcount, we can dereference the anon_vma after observing those.
451	*/
452	struct anon_vma page_get_anon_vma(struct page page)
453	{
454	struct anon_vma *anon_vma = NULL;
455	unsigned long anon_mapping;
456
457	rcu_read_lock();
458	anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
459	if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
460	goto out;
461	if (!page_mapped(page))
462	goto out;
463
464	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
465	if (!atomic_inc_not_zero(&anon_vma->refcount)) {
466	anon_vma = NULL;
467	goto out;
468	}
469
470	/*
471	* If this page is still mapped, then its anon_vma cannot have been
472	* freed. But if it has been unmapped, we have no security against the
473	* anon_vma structure being freed and reused (for another anon_vma:
474	* SLAB_DESTROY_BY_RCU guarantees that - so the atomic_inc_not_zero()
475	* above cannot corrupt).
476	*/
477	if (!page_mapped(page)) {
478	put_anon_vma(anon_vma);
479	anon_vma = NULL;
480	}
481	out:
482	rcu_read_unlock();
483
484	return anon_vma;
485	}
486
487	/*
488	* Similar to page_get_anon_vma() except it locks the anon_vma.
489	*
490	* Its a little more complex as it tries to keep the fast path to a single
491	* atomic op -- the trylock. If we fail the trylock, we fall back to getting a
492	* reference like with page_get_anon_vma() and then block on the mutex.
493	*/
494	struct anon_vma page_lock_anon_vma(struct page page)
495	{
496	struct anon_vma *anon_vma = NULL;
497	struct anon_vma *root_anon_vma;
498	unsigned long anon_mapping;
499
500	rcu_read_lock();
501	anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
502	if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
503	goto out;
504	if (!page_mapped(page))
505	goto out;
506
507	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
508	root_anon_vma = ACCESS_ONCE(anon_vma->root);
509	if (mutex_trylock(&root_anon_vma->mutex)) {
510	/*
511	* If the page is still mapped, then this anon_vma is still
512	* its anon_vma, and holding the mutex ensures that it will
513	* not go away, see anon_vma_free().
514	*/
515	if (!page_mapped(page)) {
516	mutex_unlock(&root_anon_vma->mutex);
517	anon_vma = NULL;
518	}
519	goto out;
520	}
521
522	/* trylock failed, we got to sleep */
523	if (!atomic_inc_not_zero(&anon_vma->refcount)) {
524	anon_vma = NULL;
525	goto out;
526	}
527
528	if (!page_mapped(page)) {
529	put_anon_vma(anon_vma);
530	anon_vma = NULL;
531	goto out;
532	}
533
534	/* we pinned the anon_vma, its safe to sleep */
535	rcu_read_unlock();
536	anon_vma_lock(anon_vma);
537
538	if (atomic_dec_and_test(&anon_vma->refcount)) {
539	/*
540	* Oops, we held the last refcount, release the lock
541	* and bail -- can't simply use put_anon_vma() because
542	* we'll deadlock on the anon_vma_lock() recursion.
543	*/
544	anon_vma_unlock(anon_vma);
545	__put_anon_vma(anon_vma);
546	anon_vma = NULL;
547	}
548
549	return anon_vma;
550
551	out:
552	rcu_read_unlock();
553	return anon_vma;
554	}
555
556	void page_unlock_anon_vma(struct anon_vma *anon_vma)
557	{
558	anon_vma_unlock(anon_vma);
559	}
560
561	/*
562	* At what user virtual address is page expected in @vma?
563	* Returns virtual address or -EFAULT if page's index/offset is not
564	* within the range mapped the @vma.
565	*/
566	inline unsigned long
567	vma_address(struct page page, struct vm_area_struct vma)
568	{
569	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
570	unsigned long address;
571
572	if (unlikely(is_vm_hugetlb_page(vma)))
573	pgoff = page->index << huge_page_order(page_hstate(page));
574	address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
575	if (unlikely(address < vma->vm_start \|\| address >= vma->vm_end)) {
576	/* page should be within @vma mapping range */
577	return -EFAULT;
578	}
579	return address;
580	}
581
582	/*
583	* At what user virtual address is page expected in vma?
584	* Caller should check the page is actually part of the vma.
585	*/
586	unsigned long page_address_in_vma(struct page page, struct vm_area_struct vma)
587	{
588	if (PageAnon(page)) {
589	struct anon_vma *page__anon_vma = page_anon_vma(page);
590	/*
591	* Note: swapoff's unuse_vma() is more efficient with this
592	* check, and needs it to match anon_vma when KSM is active.
593	*/
594	if (!vma->anon_vma \|\| !page__anon_vma \|\|
595	vma->anon_vma->root != page__anon_vma->root)
596	return -EFAULT;
597	} else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
598	if (!vma->vm_file \|\|
599	vma->vm_file->f_mapping != page->mapping)
600	return -EFAULT;
601	} else
602	return -EFAULT;
603	return vma_address(page, vma);
604	}
605
606	/*
607	* Check that @page is mapped at @address into @mm.
608	*
609	* If @sync is false, page_check_address may perform a racy check to avoid
610	* the page table lock when the pte is not present (helpful when reclaiming
611	* highly shared pages).
612	*
613	* On success returns with pte mapped and locked.
614	*/
615	pte_t __page_check_address(struct page page, struct mm_struct *mm,
616	unsigned long address, spinlock_t **ptlp, int sync)
617	{
618	pgd_t *pgd;
619	pud_t *pud;
620	pmd_t *pmd;
621	pte_t *pte;
622	spinlock_t *ptl;
623
624	if (unlikely(PageHuge(page))) {
625	pte = huge_pte_offset(mm, address);
626	ptl = &mm->page_table_lock;
627	goto check;
628	}
629
630	pgd = pgd_offset(mm, address);
631	if (!pgd_present(*pgd))
632	return NULL;
633
634	pud = pud_offset(pgd, address);
635	if (!pud_present(*pud))
636	return NULL;
637
638	pmd = pmd_offset(pud, address);
639	if (!pmd_present(*pmd))
640	return NULL;
641	if (pmd_trans_huge(*pmd))
642	return NULL;
643
644	pte = pte_offset_map(pmd, address);
645	/* Make a quick check before getting the lock */
646	if (!sync && !pte_present(*pte)) {
647	pte_unmap(pte);
648	return NULL;
649	}
650
651	ptl = pte_lockptr(mm, pmd);
652	check:
653	spin_lock(ptl);
654	if (pte_present(pte) && page_to_pfn(page) == pte_pfn(pte)) {
655	*ptlp = ptl;
656	return pte;
657	}
658	pte_unmap_unlock(pte, ptl);
659	return NULL;
660	}
661
662	/**
663	* page_mapped_in_vma - check whether a page is really mapped in a VMA
664	* @page: the page to test
665	* @vma: the VMA to test
666	*
667	* Returns 1 if the page is mapped into the page tables of the VMA, 0
668	* if the page is not mapped into the page tables of this VMA. Only
669	* valid for normal file or anonymous VMAs.
670	*/
671	int page_mapped_in_vma(struct page page, struct vm_area_struct vma)
672	{
673	unsigned long address;
674	pte_t *pte;
675	spinlock_t *ptl;
676
677	address = vma_address(page, vma);
678	if (address == -EFAULT) /* out of vma range */
679	return 0;
680	pte = page_check_address(page, vma->vm_mm, address, &ptl, 1);
681	if (!pte) /* the page is not in this mm */
682	return 0;
683	pte_unmap_unlock(pte, ptl);
684
685	return 1;
686	}
687
688	/*
689	* Subfunctions of page_referenced: page_referenced_one called
690	* repeatedly from either page_referenced_anon or page_referenced_file.
691	*/
692	int page_referenced_one(struct page page, struct vm_area_struct vma,
693	unsigned long address, unsigned int *mapcount,
694	unsigned long *vm_flags)
695	{
696	struct mm_struct *mm = vma->vm_mm;
697	int referenced = 0;
698
699	if (unlikely(PageTransHuge(page))) {
700	pmd_t *pmd;
701
702	spin_lock(&mm->page_table_lock);
703	/*
704	* rmap might return false positives; we must filter
705	* these out using page_check_address_pmd().
706	*/
707	pmd = page_check_address_pmd(page, mm, address,
708	PAGE_CHECK_ADDRESS_PMD_FLAG);
709	if (!pmd) {
710	spin_unlock(&mm->page_table_lock);
711	goto out;
712	}
713
714	if (vma->vm_flags & VM_LOCKED) {
715	spin_unlock(&mm->page_table_lock);
716	mapcount = 0; / break early from loop */
717	*vm_flags \|= VM_LOCKED;
718	goto out;
719	}
720
721	/* go ahead even if the pmd is pmd_trans_splitting() */
722	if (pmdp_clear_flush_young_notify(vma, address, pmd))
723	referenced++;
724	spin_unlock(&mm->page_table_lock);
725	} else {
726	pte_t *pte;
727	spinlock_t *ptl;
728
729	/*
730	* rmap might return false positives; we must filter
731	* these out using page_check_address().
732	*/
733	pte = page_check_address(page, mm, address, &ptl, 0);
734	if (!pte)
735	goto out;
736
737	if (vma->vm_flags & VM_LOCKED) {
738	pte_unmap_unlock(pte, ptl);
739	mapcount = 0; / break early from loop */
740	*vm_flags \|= VM_LOCKED;
741	goto out;
742	}
743
744	if (ptep_clear_flush_young_notify(vma, address, pte)) {
745	/*
746	* Don't treat a reference through a sequentially read
747	* mapping as such. If the page has been used in
748	* another mapping, we will catch it; if this other
749	* mapping is already gone, the unmap path will have
750	* set PG_referenced or activated the page.
751	*/
752	if (likely(!VM_SequentialReadHint(vma)))
753	referenced++;
754	}
755	pte_unmap_unlock(pte, ptl);
756	}
757
758	(*mapcount)--;
759
760	if (referenced)
761	*vm_flags \|= vma->vm_flags;
762	out:
763	return referenced;
764	}
765
766	static int page_referenced_anon(struct page *page,
767	struct mem_cgroup *memcg,
768	unsigned long *vm_flags)
769	{
770	unsigned int mapcount;
771	struct anon_vma *anon_vma;
772	struct anon_vma_chain *avc;
773	int referenced = 0;
774
775	anon_vma = page_lock_anon_vma(page);
776	if (!anon_vma)
777	return referenced;
778
779	mapcount = page_mapcount(page);
780	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
781	struct vm_area_struct *vma = avc->vma;
782	unsigned long address = vma_address(page, vma);
783	if (address == -EFAULT)
784	continue;
785	/*
786	* If we are reclaiming on behalf of a cgroup, skip
787	* counting on behalf of references from different
788	* cgroups
789	*/
790	if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
791	continue;
792	referenced += page_referenced_one(page, vma, address,
793	&mapcount, vm_flags);
794	if (!mapcount)
795	break;
796	}
797
798	page_unlock_anon_vma(anon_vma);
799	return referenced;
800	}
801
802	/**
803	* page_referenced_file - referenced check for object-based rmap
804	* @page: the page we're checking references on.
805	* @memcg: target memory control group
806	* @vm_flags: collect encountered vma->vm_flags who actually referenced the page
807	*
808	* For an object-based mapped page, find all the places it is mapped and
809	* check/clear the referenced flag. This is done by following the page->mapping
810	* pointer, then walking the chain of vmas it holds. It returns the number
811	* of references it found.
812	*
813	* This function is only called from page_referenced for object-based pages.
814	*/
815	static int page_referenced_file(struct page *page,
816	struct mem_cgroup *memcg,
817	unsigned long *vm_flags)
818	{
819	unsigned int mapcount;
820	struct address_space *mapping = page->mapping;
821	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
822	struct vm_area_struct *vma;
823	struct prio_tree_iter iter;
824	int referenced = 0;
825
826	/*
827	* The caller's checks on page->mapping and !PageAnon have made
828	* sure that this is a file page: the check for page->mapping
829	* excludes the case just before it gets set on an anon page.
830	*/
831	BUG_ON(PageAnon(page));
832
833	/*
834	* The page lock not only makes sure that page->mapping cannot
835	* suddenly be NULLified by truncation, it makes sure that the
836	* structure at mapping cannot be freed and reused yet,
837	* so we can safely take mapping->i_mmap_mutex.
838	*/
839	BUG_ON(!PageLocked(page));
840
841	mutex_lock(&mapping->i_mmap_mutex);
842
843	/*
844	* i_mmap_mutex does not stabilize mapcount at all, but mapcount
845	* is more likely to be accurate if we note it after spinning.
846	*/
847	mapcount = page_mapcount(page);
848
849	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
850	unsigned long address = vma_address(page, vma);
851	if (address == -EFAULT)
852	continue;
853	/*
854	* If we are reclaiming on behalf of a cgroup, skip
855	* counting on behalf of references from different
856	* cgroups
857	*/
858	if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
859	continue;
860	referenced += page_referenced_one(page, vma, address,
861	&mapcount, vm_flags);
862	if (!mapcount)
863	break;
864	}
865
866	mutex_unlock(&mapping->i_mmap_mutex);
867	return referenced;
868	}
869
870	/**
871	* page_referenced - test if the page was referenced
872	* @page: the page to test
873	* @is_locked: caller holds lock on the page
874	* @memcg: target memory cgroup
875	* @vm_flags: collect encountered vma->vm_flags who actually referenced the page
876	*
877	* Quick test_and_clear_referenced for all mappings to a page,
878	* returns the number of ptes which referenced the page.
879	*/
880	int page_referenced(struct page *page,
881	int is_locked,
882	struct mem_cgroup *memcg,
883	unsigned long *vm_flags)
884	{
885	int referenced = 0;
886	int we_locked = 0;
887
888	*vm_flags = 0;
889	if (page_mapped(page) && page_rmapping(page)) {
890	if (!is_locked && (!PageAnon(page) \|\| PageKsm(page))) {
891	we_locked = trylock_page(page);
892	if (!we_locked) {
893	referenced++;
894	goto out;
895	}
896	}
897	if (unlikely(PageKsm(page)))
898	referenced += page_referenced_ksm(page, memcg,
899	vm_flags);
900	else if (PageAnon(page))
901	referenced += page_referenced_anon(page, memcg,
902	vm_flags);
903	else if (page->mapping)
904	referenced += page_referenced_file(page, memcg,
905	vm_flags);
906	if (we_locked)
907	unlock_page(page);
908
909	if (page_test_and_clear_young(page_to_pfn(page)))
910	referenced++;
911	}
912	out:
913	return referenced;
914	}
915
916	static int page_mkclean_one(struct page page, struct vm_area_struct vma,
917	unsigned long address)
918	{
919	struct mm_struct *mm = vma->vm_mm;
920	pte_t *pte;
921	spinlock_t *ptl;
922	int ret = 0;
923
924	pte = page_check_address(page, mm, address, &ptl, 1);
925	if (!pte)
926	goto out;
927
928	if (pte_dirty(pte) \|\| pte_write(pte)) {
929	pte_t entry;
930
931	flush_cache_page(vma, address, pte_pfn(*pte));
932	entry = ptep_clear_flush_notify(vma, address, pte);
933	entry = pte_wrprotect(entry);
934	entry = pte_mkclean(entry);
935	set_pte_at(mm, address, pte, entry);
936	ret = 1;
937	}
938
939	pte_unmap_unlock(pte, ptl);
940	out:
941	return ret;
942	}
943
944	static int page_mkclean_file(struct address_space mapping, struct page page)
945	{
946	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
947	struct vm_area_struct *vma;
948	struct prio_tree_iter iter;
949	int ret = 0;
950
951	BUG_ON(PageAnon(page));
952
953	mutex_lock(&mapping->i_mmap_mutex);
954	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
955	if (vma->vm_flags & VM_SHARED) {
956	unsigned long address = vma_address(page, vma);
957	if (address == -EFAULT)
958	continue;
959	ret += page_mkclean_one(page, vma, address);
960	}
961	}
962	mutex_unlock(&mapping->i_mmap_mutex);
963	return ret;
964	}
965
966	int page_mkclean(struct page *page)
967	{
968	int ret = 0;
969
970	BUG_ON(!PageLocked(page));
971
972	if (page_mapped(page)) {
973	struct address_space *mapping = page_mapping(page);
974	if (mapping) {
975	ret = page_mkclean_file(mapping, page);
976	if (page_test_and_clear_dirty(page_to_pfn(page), 1))
977	ret = 1;
978	}
979	}
980
981	return ret;
982	}
983	EXPORT_SYMBOL_GPL(page_mkclean);
984
985	/**
986	* page_move_anon_rmap - move a page to our anon_vma
987	* @page: the page to move to our anon_vma
988	* @vma: the vma the page belongs to
989	* @address: the user virtual address mapped
990	*
991	* When a page belongs exclusively to one process after a COW event,
992	* that page can be moved into the anon_vma that belongs to just that
993	* process, so the rmap code will not search the parent or sibling
994	* processes.
995	*/
996	void page_move_anon_rmap(struct page *page,
997	struct vm_area_struct *vma, unsigned long address)
998	{
999	struct anon_vma *anon_vma = vma->anon_vma;
1000
1001	VM_BUG_ON(!PageLocked(page));
1002	VM_BUG_ON(!anon_vma);
1003	VM_BUG_ON(page->index != linear_page_index(vma, address));
1004
1005	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1006	page->mapping = (struct address_space *) anon_vma;
1007	}
1008
1009	/**
1010	* __page_set_anon_rmap - set up new anonymous rmap
1011	* @page: Page to add to rmap
1012	* @vma: VM area to add page to.
1013	* @address: User virtual address of the mapping
1014	* @exclusive: the page is exclusively owned by the current process
1015	*/
1016	static void __page_set_anon_rmap(struct page *page,
1017	struct vm_area_struct *vma, unsigned long address, int exclusive)
1018	{
1019	struct anon_vma *anon_vma = vma->anon_vma;
1020
1021	BUG_ON(!anon_vma);
1022
1023	if (PageAnon(page))
1024	return;
1025
1026	/*
1027	* If the page isn't exclusively mapped into this vma,
1028	* we must use the _oldest_ possible anon_vma for the
1029	* page mapping!
1030	*/
1031	if (!exclusive)
1032	anon_vma = anon_vma->root;
1033
1034	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1035	page->mapping = (struct address_space *) anon_vma;
1036	page->index = linear_page_index(vma, address);
1037	}
1038
1039	/**
1040	* __page_check_anon_rmap - sanity check anonymous rmap addition
1041	* @page: the page to add the mapping to
1042	* @vma: the vm area in which the mapping is added
1043	* @address: the user virtual address mapped
1044	*/
1045	static void __page_check_anon_rmap(struct page *page,
1046	struct vm_area_struct *vma, unsigned long address)
1047	{
1048	#ifdef CONFIG_DEBUG_VM
1049	/*
1050	* The page's anon-rmap details (mapping and index) are guaranteed to
1051	* be set up correctly at this point.
1052	*
1053	* We have exclusion against page_add_anon_rmap because the caller
1054	* always holds the page locked, except if called from page_dup_rmap,
1055	* in which case the page is already known to be setup.
1056	*
1057	* We have exclusion against page_add_new_anon_rmap because those pages
1058	* are initially only visible via the pagetables, and the pte is locked
1059	* over the call to page_add_new_anon_rmap.
1060	*/
1061	BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root);
1062	BUG_ON(page->index != linear_page_index(vma, address));
1063	#endif
1064	}
1065
1066	/**
1067	* page_add_anon_rmap - add pte mapping to an anonymous page
1068	* @page: the page to add the mapping to
1069	* @vma: the vm area in which the mapping is added
1070	* @address: the user virtual address mapped
1071	*
1072	* The caller needs to hold the pte lock, and the page must be locked in
1073	* the anon_vma case: to serialize mapping,index checking after setting,
1074	* and to ensure that PageAnon is not being upgraded racily to PageKsm
1075	* (but PageKsm is never downgraded to PageAnon).
1076	*/
1077	void page_add_anon_rmap(struct page *page,
1078	struct vm_area_struct *vma, unsigned long address)
1079	{
1080	do_page_add_anon_rmap(page, vma, address, 0);
1081	}
1082
1083	/*
1084	* Special version of the above for do_swap_page, which often runs
1085	* into pages that are exclusively owned by the current process.
1086	* Everybody else should continue to use page_add_anon_rmap above.
1087	*/
1088	void do_page_add_anon_rmap(struct page *page,
1089	struct vm_area_struct *vma, unsigned long address, int exclusive)
1090	{
1091	int first = atomic_inc_and_test(&page->_mapcount);
1092	if (first) {
1093	if (!PageTransHuge(page))
1094	__inc_zone_page_state(page, NR_ANON_PAGES);
1095	else
1096	__inc_zone_page_state(page,
1097	NR_ANON_TRANSPARENT_HUGEPAGES);
1098	}
1099	if (unlikely(PageKsm(page)))
1100	return;
1101
1102	VM_BUG_ON(!PageLocked(page));
1103	/* address might be in next vma when migration races vma_adjust */
1104	if (first)
1105	__page_set_anon_rmap(page, vma, address, exclusive);
1106	else
1107	__page_check_anon_rmap(page, vma, address);
1108	}
1109
1110	/**
1111	* page_add_new_anon_rmap - add pte mapping to a new anonymous page
1112	* @page: the page to add the mapping to
1113	* @vma: the vm area in which the mapping is added
1114	* @address: the user virtual address mapped
1115	*
1116	* Same as page_add_anon_rmap but must only be called on new pages.
1117	* This means the inc-and-test can be bypassed.
1118	* Page does not have to be locked.
1119	*/
1120	void page_add_new_anon_rmap(struct page *page,
1121	struct vm_area_struct *vma, unsigned long address)
1122	{
1123	VM_BUG_ON(address < vma->vm_start \|\| address >= vma->vm_end);
1124	SetPageSwapBacked(page);
1125	atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
1126	if (!PageTransHuge(page))
1127	__inc_zone_page_state(page, NR_ANON_PAGES);
1128	else
1129	__inc_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
1130	__page_set_anon_rmap(page, vma, address, 1);
1131	if (page_evictable(page, vma))
1132	lru_cache_add_lru(page, LRU_ACTIVE_ANON);
1133	else
1134	add_page_to_unevictable_list(page);
1135	}
1136
1137	/**
1138	* page_add_file_rmap - add pte mapping to a file page
1139	* @page: the page to add the mapping to
1140	*
1141	* The caller needs to hold the pte lock.
1142	*/
1143	void page_add_file_rmap(struct page *page)
1144	{
1145	bool locked;
1146	unsigned long flags;
1147
1148	mem_cgroup_begin_update_page_stat(page, &locked, &flags);
1149	if (atomic_inc_and_test(&page->_mapcount)) {
1150	__inc_zone_page_state(page, NR_FILE_MAPPED);
1151	mem_cgroup_inc_page_stat(page, MEMCG_NR_FILE_MAPPED);
1152	}
1153	mem_cgroup_end_update_page_stat(page, &locked, &flags);
1154	}
1155
1156	/**
1157	* page_remove_rmap - take down pte mapping from a page
1158	* @page: page to remove mapping from
1159	*
1160	* The caller needs to hold the pte lock.
1161	*/
1162	void page_remove_rmap(struct page *page)
1163	{
1164	bool anon = PageAnon(page);
1165	bool locked;
1166	unsigned long flags;
1167
1168	/*
1169	* The anon case has no mem_cgroup page_stat to update; but may
1170	* uncharge_page() below, where the lock ordering can deadlock if
1171	* we hold the lock against page_stat move: so avoid it on anon.
1172	*/
1173	if (!anon)
1174	mem_cgroup_begin_update_page_stat(page, &locked, &flags);
1175
1176	/* page still mapped by someone else? */
1177	if (!atomic_add_negative(-1, &page->_mapcount))
1178	goto out;
1179
1180	/*
1181	* Now that the last pte has gone, s390 must transfer dirty
1182	* flag from storage key to struct page. We can usually skip
1183	* this if the page is anon, so about to be freed; but perhaps
1184	* not if it's in swapcache - there might be another pte slot
1185	* containing the swap entry, but page not yet written to swap.
1186	*/
1187	if ((!anon \|\| PageSwapCache(page)) &&
1188	page_test_and_clear_dirty(page_to_pfn(page), 1))
1189	set_page_dirty(page);
1190	/*
1191	* Hugepages are not counted in NR_ANON_PAGES nor NR_FILE_MAPPED
1192	* and not charged by memcg for now.
1193	*/
1194	if (unlikely(PageHuge(page)))
1195	goto out;
1196	if (anon) {
1197	mem_cgroup_uncharge_page(page);
1198	if (!PageTransHuge(page))
1199	__dec_zone_page_state(page, NR_ANON_PAGES);
1200	else
1201	__dec_zone_page_state(page,
1202	NR_ANON_TRANSPARENT_HUGEPAGES);
1203	} else {
1204	__dec_zone_page_state(page, NR_FILE_MAPPED);
1205	mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
1206	}
1207	/*
1208	* It would be tidy to reset the PageAnon mapping here,
1209	* but that might overwrite a racing page_add_anon_rmap
1210	* which increments mapcount after us but sets mapping
1211	* before us: so leave the reset to free_hot_cold_page,
1212	* and remember that it's only reliable while mapped.
1213	* Leaving it set also helps swapoff to reinstate ptes
1214	* faster for those pages still in swapcache.
1215	*/
1216	out:
1217	if (!anon)
1218	mem_cgroup_end_update_page_stat(page, &locked, &flags);
1219	}
1220
1221	/*
1222	* Subfunctions of try_to_unmap: try_to_unmap_one called
1223	* repeatedly from try_to_unmap_ksm, try_to_unmap_anon or try_to_unmap_file.
1224	*/
1225	int try_to_unmap_one(struct page page, struct vm_area_struct vma,
1226	unsigned long address, enum ttu_flags flags)
1227	{
1228	struct mm_struct *mm = vma->vm_mm;
1229	pte_t *pte;
1230	pte_t pteval;
1231	spinlock_t *ptl;
1232	int ret = SWAP_AGAIN;
1233
1234	pte = page_check_address(page, mm, address, &ptl, 0);
1235	if (!pte)
1236	goto out;
1237
1238	/*
1239	* If the page is mlock()d, we cannot swap it out.
1240	* If it's recently referenced (perhaps page_referenced
1241	* skipped over this mm) then we should reactivate it.
1242	*/
1243	if (!(flags & TTU_IGNORE_MLOCK)) {
1244	if (vma->vm_flags & VM_LOCKED)
1245	goto out_mlock;
1246
1247	if (TTU_ACTION(flags) == TTU_MUNLOCK)
1248	goto out_unmap;
1249	}
1250	if (!(flags & TTU_IGNORE_ACCESS)) {
1251	if (ptep_clear_flush_young_notify(vma, address, pte)) {
1252	ret = SWAP_FAIL;
1253	goto out_unmap;
1254	}
1255	}
1256
1257	/* Nuke the page table entry. */
1258	flush_cache_page(vma, address, page_to_pfn(page));
1259	pteval = ptep_clear_flush_notify(vma, address, pte);
1260
1261	/* Move the dirty bit to the physical page now the pte is gone. */
1262	if (pte_dirty(pteval))
1263	set_page_dirty(page);
1264
1265	/* Update high watermark before we lower rss */
1266	update_hiwater_rss(mm);
1267
1268	if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {
1269	if (PageAnon(page))
1270	dec_mm_counter(mm, MM_ANONPAGES);
1271	else
1272	dec_mm_counter(mm, MM_FILEPAGES);
1273	set_pte_at(mm, address, pte,
1274	swp_entry_to_pte(make_hwpoison_entry(page)));
1275	} else if (PageAnon(page)) {
1276	swp_entry_t entry = { .val = page_private(page) };
1277
1278	if (PageSwapCache(page)) {
1279	/*
1280	* Store the swap location in the pte.
1281	* See handle_pte_fault() ...
1282	*/
1283	if (swap_duplicate(entry) < 0) {
1284	set_pte_at(mm, address, pte, pteval);
1285	ret = SWAP_FAIL;
1286	goto out_unmap;
1287	}
1288	if (list_empty(&mm->mmlist)) {
1289	spin_lock(&mmlist_lock);
1290	if (list_empty(&mm->mmlist))
1291	list_add(&mm->mmlist, &init_mm.mmlist);
1292	spin_unlock(&mmlist_lock);
1293	}
1294	dec_mm_counter(mm, MM_ANONPAGES);
1295	inc_mm_counter(mm, MM_SWAPENTS);
1296	} else if (IS_ENABLED(CONFIG_MIGRATION)) {
1297	/*
1298	* Store the pfn of the page in a special migration
1299	* pte. do_swap_page() will wait until the migration
1300	* pte is removed and then restart fault handling.
1301	*/
1302	BUG_ON(TTU_ACTION(flags) != TTU_MIGRATION);
1303	entry = make_migration_entry(page, pte_write(pteval));
1304	}
1305	set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
1306	BUG_ON(pte_file(*pte));
1307	} else if (IS_ENABLED(CONFIG_MIGRATION) &&
1308	(TTU_ACTION(flags) == TTU_MIGRATION)) {
1309	/* Establish migration entry for a file page */
1310	swp_entry_t entry;
1311	entry = make_migration_entry(page, pte_write(pteval));
1312	set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
1313	} else
1314	dec_mm_counter(mm, MM_FILEPAGES);
1315
1316	page_remove_rmap(page);
1317	page_cache_release(page);
1318
1319	out_unmap:
1320	pte_unmap_unlock(pte, ptl);
1321	out:
1322	return ret;
1323
1324	out_mlock:
1325	pte_unmap_unlock(pte, ptl);
1326
1327
1328	/*
1329	* We need mmap_sem locking, Otherwise VM_LOCKED check makes
1330	* unstable result and race. Plus, We can't wait here because
1331	* we now hold anon_vma->mutex or mapping->i_mmap_mutex.
1332	* if trylock failed, the page remain in evictable lru and later
1333	* vmscan could retry to move the page to unevictable lru if the
1334	* page is actually mlocked.
1335	*/
1336	if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
1337	if (vma->vm_flags & VM_LOCKED) {
1338	mlock_vma_page(page);
1339	ret = SWAP_MLOCK;
1340	}
1341	up_read(&vma->vm_mm->mmap_sem);
1342	}
1343	return ret;
1344	}
1345
1346	/*
1347	* objrmap doesn't work for nonlinear VMAs because the assumption that
1348	* offset-into-file correlates with offset-into-virtual-addresses does not hold.
1349	* Consequently, given a particular page and its ->index, we cannot locate the
1350	* ptes which are mapping that page without an exhaustive linear search.
1351	*
1352	* So what this code does is a mini "virtual scan" of each nonlinear VMA which
1353	* maps the file to which the target page belongs. The ->vm_private_data field
1354	* holds the current cursor into that scan. Successive searches will circulate
1355	* around the vma's virtual address space.
1356	*
1357	* So as more replacement pressure is applied to the pages in a nonlinear VMA,
1358	* more scanning pressure is placed against them as well. Eventually pages
1359	* will become fully unmapped and are eligible for eviction.
1360	*
1361	* For very sparsely populated VMAs this is a little inefficient - chances are
1362	* there there won't be many ptes located within the scan cluster. In this case
1363	* maybe we could scan further - to the end of the pte page, perhaps.
1364	*
1365	* Mlocked pages: check VM_LOCKED under mmap_sem held for read, if we can
1366	* acquire it without blocking. If vma locked, mlock the pages in the cluster,
1367	* rather than unmapping them. If we encounter the "check_page" that vmscan is
1368	* trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN.
1369	*/
1370	#define CLUSTER_SIZE min(32*PAGE_SIZE, PMD_SIZE)
1371	#define CLUSTER_MASK (~(CLUSTER_SIZE - 1))
1372
1373	static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
1374	struct vm_area_struct vma, struct page check_page)
1375	{
1376	struct mm_struct *mm = vma->vm_mm;
1377	pgd_t *pgd;
1378	pud_t *pud;
1379	pmd_t *pmd;
1380	pte_t *pte;
1381	pte_t pteval;
1382	spinlock_t *ptl;
1383	struct page *page;
1384	unsigned long address;
1385	unsigned long end;
1386	int ret = SWAP_AGAIN;
1387	int locked_vma = 0;
1388
1389	address = (vma->vm_start + cursor) & CLUSTER_MASK;
1390	end = address + CLUSTER_SIZE;
1391	if (address < vma->vm_start)
1392	address = vma->vm_start;
1393	if (end > vma->vm_end)
1394	end = vma->vm_end;
1395
1396	pgd = pgd_offset(mm, address);
1397	if (!pgd_present(*pgd))
1398	return ret;
1399
1400	pud = pud_offset(pgd, address);
1401	if (!pud_present(*pud))
1402	return ret;
1403
1404	pmd = pmd_offset(pud, address);
1405	if (!pmd_present(*pmd))
1406	return ret;
1407
1408	/*
1409	* If we can acquire the mmap_sem for read, and vma is VM_LOCKED,
1410	* keep the sem while scanning the cluster for mlocking pages.
1411	*/
1412	if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
1413	locked_vma = (vma->vm_flags & VM_LOCKED);
1414	if (!locked_vma)
1415	up_read(&vma->vm_mm->mmap_sem); /* don't need it */
1416	}
1417
1418	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1419
1420	/* Update high watermark before we lower rss */
1421	update_hiwater_rss(mm);
1422
1423	for (; address < end; pte++, address += PAGE_SIZE) {
1424	if (!pte_present(*pte))
1425	continue;
1426	page = vm_normal_page(vma, address, *pte);
1427	BUG_ON(!page \|\| PageAnon(page));
1428
1429	if (locked_vma) {
1430	mlock_vma_page(page); /* no-op if already mlocked */
1431	if (page == check_page)
1432	ret = SWAP_MLOCK;
1433	continue; /* don't unmap */
1434	}
1435
1436	if (ptep_clear_flush_young_notify(vma, address, pte))
1437	continue;
1438
1439	/* Nuke the page table entry. */
1440	flush_cache_page(vma, address, pte_pfn(*pte));
1441	pteval = ptep_clear_flush_notify(vma, address, pte);
1442
1443	/* If nonlinear, store the file page offset in the pte. */
1444	if (page->index != linear_page_index(vma, address))
1445	set_pte_at(mm, address, pte, pgoff_to_pte(page->index));
1446
1447	/* Move the dirty bit to the physical page now the pte is gone. */
1448	if (pte_dirty(pteval))
1449	set_page_dirty(page);
1450
1451	page_remove_rmap(page);
1452	page_cache_release(page);
1453	dec_mm_counter(mm, MM_FILEPAGES);
1454	(*mapcount)--;
1455	}
1456	pte_unmap_unlock(pte - 1, ptl);
1457	if (locked_vma)
1458	up_read(&vma->vm_mm->mmap_sem);
1459	return ret;
1460	}
1461
1462	bool is_vma_temporary_stack(struct vm_area_struct *vma)
1463	{
1464	int maybe_stack = vma->vm_flags & (VM_GROWSDOWN \| VM_GROWSUP);
1465
1466	if (!maybe_stack)
1467	return false;
1468
1469	if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
1470	VM_STACK_INCOMPLETE_SETUP)
1471	return true;
1472
1473	return false;
1474	}
1475
1476	/**
1477	* try_to_unmap_anon - unmap or unlock anonymous page using the object-based
1478	* rmap method
1479	* @page: the page to unmap/unlock
1480	* @flags: action and flags
1481	*
1482	* Find all the mappings of a page using the mapping pointer and the vma chains
1483	* contained in the anon_vma struct it points to.
1484	*
1485	* This function is only called from try_to_unmap/try_to_munlock for
1486	* anonymous pages.
1487	* When called from try_to_munlock(), the mmap_sem of the mm containing the vma
1488	* where the page was found will be held for write. So, we won't recheck
1489	* vm_flags for that VMA. That should be OK, because that vma shouldn't be
1490	* 'LOCKED.
1491	*/
1492	static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
1493	{
1494	struct anon_vma *anon_vma;
1495	struct anon_vma_chain *avc;
1496	int ret = SWAP_AGAIN;
1497
1498	anon_vma = page_lock_anon_vma(page);
1499	if (!anon_vma)
1500	return ret;
1501
1502	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
1503	struct vm_area_struct *vma = avc->vma;
1504	unsigned long address;
1505
1506	/*
1507	* During exec, a temporary VMA is setup and later moved.
1508	* The VMA is moved under the anon_vma lock but not the
1509	* page tables leading to a race where migration cannot
1510	* find the migration ptes. Rather than increasing the
1511	* locking requirements of exec(), migration skips
1512	* temporary VMAs until after exec() completes.
1513	*/
1514	if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) &&
1515	is_vma_temporary_stack(vma))
1516	continue;
1517
1518	address = vma_address(page, vma);
1519	if (address == -EFAULT)
1520	continue;
1521	ret = try_to_unmap_one(page, vma, address, flags);
1522	if (ret != SWAP_AGAIN \|\| !page_mapped(page))
1523	break;
1524	}
1525
1526	page_unlock_anon_vma(anon_vma);
1527	return ret;
1528	}
1529
1530	/**
1531	* try_to_unmap_file - unmap/unlock file page using the object-based rmap method
1532	* @page: the page to unmap/unlock
1533	* @flags: action and flags
1534	*
1535	* Find all the mappings of a page using the mapping pointer and the vma chains
1536	* contained in the address_space struct it points to.
1537	*
1538	* This function is only called from try_to_unmap/try_to_munlock for
1539	* object-based pages.
1540	* When called from try_to_munlock(), the mmap_sem of the mm containing the vma
1541	* where the page was found will be held for write. So, we won't recheck
1542	* vm_flags for that VMA. That should be OK, because that vma shouldn't be
1543	* 'LOCKED.
1544	*/
1545	static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
1546	{
1547	struct address_space *mapping = page->mapping;
1548	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1549	struct vm_area_struct *vma;
1550	struct prio_tree_iter iter;
1551	int ret = SWAP_AGAIN;
1552	unsigned long cursor;
1553	unsigned long max_nl_cursor = 0;
1554	unsigned long max_nl_size = 0;
1555	unsigned int mapcount;
1556
1557	mutex_lock(&mapping->i_mmap_mutex);
1558	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
1559	unsigned long address = vma_address(page, vma);
1560	if (address == -EFAULT)
1561	continue;
1562	ret = try_to_unmap_one(page, vma, address, flags);
1563	if (ret != SWAP_AGAIN \|\| !page_mapped(page))
1564	goto out;
1565	}
1566
1567	if (list_empty(&mapping->i_mmap_nonlinear))
1568	goto out;
1569
1570	/*
1571	* We don't bother to try to find the munlocked page in nonlinears.
1572	* It's costly. Instead, later, page reclaim logic may call
1573	* try_to_unmap(TTU_MUNLOCK) and recover PG_mlocked lazily.
1574	*/
1575	if (TTU_ACTION(flags) == TTU_MUNLOCK)
1576	goto out;
1577
1578	list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
1579	shared.vm_set.list) {
1580	cursor = (unsigned long) vma->vm_private_data;
1581	if (cursor > max_nl_cursor)
1582	max_nl_cursor = cursor;
1583	cursor = vma->vm_end - vma->vm_start;
1584	if (cursor > max_nl_size)
1585	max_nl_size = cursor;
1586	}
1587
1588	if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */
1589	ret = SWAP_FAIL;
1590	goto out;
1591	}
1592
1593	/*
1594	* We don't try to search for this page in the nonlinear vmas,
1595	* and page_referenced wouldn't have found it anyway. Instead
1596	* just walk the nonlinear vmas trying to age and unmap some.
1597	* The mapcount of the page we came in with is irrelevant,
1598	* but even so use it as a guide to how hard we should try?
1599	*/
1600	mapcount = page_mapcount(page);
1601	if (!mapcount)
1602	goto out;
1603	cond_resched();
1604
1605	max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
1606	if (max_nl_cursor == 0)
1607	max_nl_cursor = CLUSTER_SIZE;
1608
1609	do {
1610	list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
1611	shared.vm_set.list) {
1612	cursor = (unsigned long) vma->vm_private_data;
1613	while ( cursor < max_nl_cursor &&
1614	cursor < vma->vm_end - vma->vm_start) {
1615	if (try_to_unmap_cluster(cursor, &mapcount,
1616	vma, page) == SWAP_MLOCK)
1617	ret = SWAP_MLOCK;
1618	cursor += CLUSTER_SIZE;
1619	vma->vm_private_data = (void *) cursor;
1620	if ((int)mapcount <= 0)
1621	goto out;
1622	}
1623	vma->vm_private_data = (void *) max_nl_cursor;
1624	}
1625	cond_resched();
1626	max_nl_cursor += CLUSTER_SIZE;
1627	} while (max_nl_cursor <= max_nl_size);
1628
1629	/*
1630	* Don't loop forever (perhaps all the remaining pages are
1631	* in locked vmas). Reset cursor on all unreserved nonlinear
1632	* vmas, now forgetting on which ones it had fallen behind.
1633	*/
1634	list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
1635	vma->vm_private_data = NULL;
1636	out:
1637	mutex_unlock(&mapping->i_mmap_mutex);
1638	return ret;
1639	}
1640
1641	/**
1642	* try_to_unmap - try to remove all page table mappings to a page
1643	* @page: the page to get unmapped
1644	* @flags: action and flags
1645	*
1646	* Tries to remove all the page table entries which are mapping this
1647	* page, used in the pageout path. Caller must hold the page lock.
1648	* Return values are:
1649	*
1650	* SWAP_SUCCESS - we succeeded in removing all mappings
1651	* SWAP_AGAIN - we missed a mapping, try again later
1652	* SWAP_FAIL - the page is unswappable
1653	* SWAP_MLOCK - page is mlocked.
1654	*/
1655	int try_to_unmap(struct page *page, enum ttu_flags flags)
1656	{
1657	int ret;
1658
1659	BUG_ON(!PageLocked(page));
1660	VM_BUG_ON(!PageHuge(page) && PageTransHuge(page));
1661
1662	if (unlikely(PageKsm(page)))
1663	ret = try_to_unmap_ksm(page, flags);
1664	else if (PageAnon(page))
1665	ret = try_to_unmap_anon(page, flags);
1666	else
1667	ret = try_to_unmap_file(page, flags);
1668	if (ret != SWAP_MLOCK && !page_mapped(page))
1669	ret = SWAP_SUCCESS;
1670	return ret;
1671	}
1672
1673	/**
1674	* try_to_munlock - try to munlock a page
1675	* @page: the page to be munlocked
1676	*
1677	* Called from munlock code. Checks all of the VMAs mapping the page
1678	* to make sure nobody else has this page mlocked. The page will be
1679	* returned with PG_mlocked cleared if no other vmas have it mlocked.
1680	*
1681	* Return values are:
1682	*
1683	* SWAP_AGAIN - no vma is holding page mlocked, or,
1684	* SWAP_AGAIN - page mapped in mlocked vma -- couldn't acquire mmap sem
1685	* SWAP_FAIL - page cannot be located at present
1686	* SWAP_MLOCK - page is now mlocked.
1687	*/
1688	int try_to_munlock(struct page *page)
1689	{
1690	VM_BUG_ON(!PageLocked(page) \|\| PageLRU(page));
1691
1692	if (unlikely(PageKsm(page)))
1693	return try_to_unmap_ksm(page, TTU_MUNLOCK);
1694	else if (PageAnon(page))
1695	return try_to_unmap_anon(page, TTU_MUNLOCK);
1696	else
1697	return try_to_unmap_file(page, TTU_MUNLOCK);
1698	}
1699
1700	void __put_anon_vma(struct anon_vma *anon_vma)
1701	{
1702	struct anon_vma *root = anon_vma->root;
1703
1704	if (root != anon_vma && atomic_dec_and_test(&root->refcount))
1705	anon_vma_free(root);
1706
1707	anon_vma_free(anon_vma);
1708	}
1709
1710	#ifdef CONFIG_MIGRATION
1711	/*
1712	* rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file():
1713	* Called by migrate.c to remove migration ptes, but might be used more later.
1714	*/
1715	static int rmap_walk_anon(struct page page, int (rmap_one)(struct page *,
1716	struct vm_area_struct , unsigned long, void ), void *arg)
1717	{
1718	struct anon_vma *anon_vma;
1719	struct anon_vma_chain *avc;
1720	int ret = SWAP_AGAIN;
1721
1722	/*
1723	* Note: remove_migration_ptes() cannot use page_lock_anon_vma()
1724	* because that depends on page_mapped(); but not all its usages
1725	* are holding mmap_sem. Users without mmap_sem are required to
1726	* take a reference count to prevent the anon_vma disappearing
1727	*/
1728	anon_vma = page_anon_vma(page);
1729	if (!anon_vma)
1730	return ret;
1731	anon_vma_lock(anon_vma);
1732	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
1733	struct vm_area_struct *vma = avc->vma;
1734	unsigned long address = vma_address(page, vma);
1735	if (address == -EFAULT)
1736	continue;
1737	ret = rmap_one(page, vma, address, arg);
1738	if (ret != SWAP_AGAIN)
1739	break;
1740	}
1741	anon_vma_unlock(anon_vma);
1742	return ret;
1743	}
1744
1745	static int rmap_walk_file(struct page page, int (rmap_one)(struct page *,
1746	struct vm_area_struct , unsigned long, void ), void *arg)
1747	{
1748	struct address_space *mapping = page->mapping;
1749	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1750	struct vm_area_struct *vma;
1751	struct prio_tree_iter iter;
1752	int ret = SWAP_AGAIN;
1753
1754	if (!mapping)
1755	return ret;
1756	mutex_lock(&mapping->i_mmap_mutex);
1757	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
1758	unsigned long address = vma_address(page, vma);
1759	if (address == -EFAULT)
1760	continue;
1761	ret = rmap_one(page, vma, address, arg);
1762	if (ret != SWAP_AGAIN)
1763	break;
1764	}
1765	/*
1766	* No nonlinear handling: being always shared, nonlinear vmas
1767	* never contain migration ptes. Decide what to do about this
1768	* limitation to linear when we need rmap_walk() on nonlinear.
1769	*/
1770	mutex_unlock(&mapping->i_mmap_mutex);
1771	return ret;
1772	}
1773
1774	int rmap_walk(struct page page, int (rmap_one)(struct page *,
1775	struct vm_area_struct , unsigned long, void ), void *arg)
1776	{
1777	VM_BUG_ON(!PageLocked(page));
1778
1779	if (unlikely(PageKsm(page)))
1780	return rmap_walk_ksm(page, rmap_one, arg);
1781	else if (PageAnon(page))
1782	return rmap_walk_anon(page, rmap_one, arg);
1783	else
1784	return rmap_walk_file(page, rmap_one, arg);
1785	}
1786	#endif /* CONFIG_MIGRATION */
1787
1788	#ifdef CONFIG_HUGETLB_PAGE
1789	/*
1790	* The following three functions are for anonymous (private mapped) hugepages.
1791	* Unlike common anonymous pages, anonymous hugepages have no accounting code
1792	* and no lru code, because we handle hugepages differently from common pages.
1793	*/
1794	static void __hugepage_set_anon_rmap(struct page *page,
1795	struct vm_area_struct *vma, unsigned long address, int exclusive)
1796	{
1797	struct anon_vma *anon_vma = vma->anon_vma;
1798
1799	BUG_ON(!anon_vma);
1800
1801	if (PageAnon(page))
1802	return;
1803	if (!exclusive)
1804	anon_vma = anon_vma->root;
1805
1806	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1807	page->mapping = (struct address_space *) anon_vma;
1808	page->index = linear_page_index(vma, address);
1809	}
1810
1811	void hugepage_add_anon_rmap(struct page *page,
1812	struct vm_area_struct *vma, unsigned long address)
1813	{
1814	struct anon_vma *anon_vma = vma->anon_vma;
1815	int first;
1816
1817	BUG_ON(!PageLocked(page));
1818	BUG_ON(!anon_vma);
1819	/* address might be in next vma when migration races vma_adjust */
1820	first = atomic_inc_and_test(&page->_mapcount);
1821	if (first)
1822	__hugepage_set_anon_rmap(page, vma, address, 0);
1823	}
1824
1825	void hugepage_add_new_anon_rmap(struct page *page,
1826	struct vm_area_struct *vma, unsigned long address)
1827	{
1828	BUG_ON(address < vma->vm_start \|\| address >= vma->vm_end);
1829	atomic_set(&page->_mapcount, 0);
1830	__hugepage_set_anon_rmap(page, vma, address, 1);
1831	}
1832	#endif /* CONFIG_HUGETLB_PAGE */
1833

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