summaryrefslogtreecommitdiff
path: root/include/linux/rmap.h
blob: bd3504d11b15590f0e41232e234eebc1149baad4 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_RMAP_H
#define _LINUX_RMAP_H
/*
 * Declarations for Reverse Mapping functions in mm/rmap.c
 */

#include <linux/list.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/rwsem.h>
#include <linux/memcontrol.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/memremap.h>

/*
 * The anon_vma heads a list of private "related" vmas, to scan if
 * an anonymous page pointing to this anon_vma needs to be unmapped:
 * the vmas on the list will be related by forking, or by splitting.
 *
 * Since vmas come and go as they are split and merged (particularly
 * in mprotect), the mapping field of an anonymous page cannot point
 * directly to a vma: instead it points to an anon_vma, on whose list
 * the related vmas can be easily linked or unlinked.
 *
 * After unlinking the last vma on the list, we must garbage collect
 * the anon_vma object itself: we're guaranteed no page can be
 * pointing to this anon_vma once its vma list is empty.
 */
struct anon_vma {
	struct anon_vma *root;		/* Root of this anon_vma tree */
	struct rw_semaphore rwsem;	/* W: modification, R: walking the list */
	/*
	 * The refcount is taken on an anon_vma when there is no
	 * guarantee that the vma of page tables will exist for
	 * the duration of the operation. A caller that takes
	 * the reference is responsible for clearing up the
	 * anon_vma if they are the last user on release
	 */
	atomic_t refcount;

	/*
	 * Count of child anon_vmas. Equals to the count of all anon_vmas that
	 * have ->parent pointing to this one, including itself.
	 *
	 * This counter is used for making decision about reusing anon_vma
	 * instead of forking new one. See comments in function anon_vma_clone.
	 */
	unsigned long num_children;
	/* Count of VMAs whose ->anon_vma pointer points to this object. */
	unsigned long num_active_vmas;

	struct anon_vma *parent;	/* Parent of this anon_vma */

	/*
	 * NOTE: the LSB of the rb_root.rb_node is set by
	 * mm_take_all_locks() _after_ taking the above lock. So the
	 * rb_root must only be read/written after taking the above lock
	 * to be sure to see a valid next pointer. The LSB bit itself
	 * is serialized by a system wide lock only visible to
	 * mm_take_all_locks() (mm_all_locks_mutex).
	 */

	/* Interval tree of private "related" vmas */
	struct rb_root_cached rb_root;
};

/*
 * The copy-on-write semantics of fork mean that an anon_vma
 * can become associated with multiple processes. Furthermore,
 * each child process will have its own anon_vma, where new
 * pages for that process are instantiated.
 *
 * This structure allows us to find the anon_vmas associated
 * with a VMA, or the VMAs associated with an anon_vma.
 * The "same_vma" list contains the anon_vma_chains linking
 * all the anon_vmas associated with this VMA.
 * The "rb" field indexes on an interval tree the anon_vma_chains
 * which link all the VMAs associated with this anon_vma.
 */
struct anon_vma_chain {
	struct vm_area_struct *vma;
	struct anon_vma *anon_vma;
	struct list_head same_vma;   /* locked by mmap_lock & page_table_lock */
	struct rb_node rb;			/* locked by anon_vma->rwsem */
	unsigned long rb_subtree_last;
#ifdef CONFIG_DEBUG_VM_RB
	unsigned long cached_vma_start, cached_vma_last;
#endif
};

enum ttu_flags {
	TTU_SPLIT_HUGE_PMD	= 0x4,	/* split huge PMD if any */
	TTU_IGNORE_MLOCK	= 0x8,	/* ignore mlock */
	TTU_SYNC		= 0x10,	/* avoid racy checks with PVMW_SYNC */
	TTU_IGNORE_HWPOISON	= 0x20,	/* corrupted page is recoverable */
	TTU_BATCH_FLUSH		= 0x40,	/* Batch TLB flushes where possible
					 * and caller guarantees they will
					 * do a final flush if necessary */
	TTU_RMAP_LOCKED		= 0x80,	/* do not grab rmap lock:
					 * caller holds it */
};

#ifdef CONFIG_MMU
static inline void get_anon_vma(struct anon_vma *anon_vma)
{
	atomic_inc(&anon_vma->refcount);
}

void __put_anon_vma(struct anon_vma *anon_vma);

static inline void put_anon_vma(struct anon_vma *anon_vma)
{
	if (atomic_dec_and_test(&anon_vma->refcount))
		__put_anon_vma(anon_vma);
}

static inline void anon_vma_lock_write(struct anon_vma *anon_vma)
{
	down_write(&anon_vma->root->rwsem);
}

static inline void anon_vma_unlock_write(struct anon_vma *anon_vma)
{
	up_write(&anon_vma->root->rwsem);
}

static inline void anon_vma_lock_read(struct anon_vma *anon_vma)
{
	down_read(&anon_vma->root->rwsem);
}

static inline int anon_vma_trylock_read(struct anon_vma *anon_vma)
{
	return down_read_trylock(&anon_vma->root->rwsem);
}

static inline void anon_vma_unlock_read(struct anon_vma *anon_vma)
{
	up_read(&anon_vma->root->rwsem);
}


/*
 * anon_vma helper functions.
 */
void anon_vma_init(void);	/* create anon_vma_cachep */
int  __anon_vma_prepare(struct vm_area_struct *);
void unlink_anon_vmas(struct vm_area_struct *);
int anon_vma_clone(struct vm_area_struct *, struct vm_area_struct *);
int anon_vma_fork(struct vm_area_struct *, struct vm_area_struct *);

static inline int anon_vma_prepare(struct vm_area_struct *vma)
{
	if (likely(vma->anon_vma))
		return 0;

	return __anon_vma_prepare(vma);
}

static inline void anon_vma_merge(struct vm_area_struct *vma,
				  struct vm_area_struct *next)
{
	VM_BUG_ON_VMA(vma->anon_vma != next->anon_vma, vma);
	unlink_anon_vmas(next);
}

struct anon_vma *folio_get_anon_vma(struct folio *folio);

/* RMAP flags, currently only relevant for some anon rmap operations. */
typedef int __bitwise rmap_t;

/*
 * No special request: if the page is a subpage of a compound page, it is
 * mapped via a PTE. The mapped (sub)page is possibly shared between processes.
 */
#define RMAP_NONE		((__force rmap_t)0)

/* The (sub)page is exclusive to a single process. */
#define RMAP_EXCLUSIVE		((__force rmap_t)BIT(0))

/*
 * The compound page is not mapped via PTEs, but instead via a single PMD and
 * should be accounted accordingly.
 */
#define RMAP_COMPOUND		((__force rmap_t)BIT(1))

/*
 * rmap interfaces called when adding or removing pte of page
 */
void page_move_anon_rmap(struct page *, struct vm_area_struct *);
void page_add_anon_rmap(struct page *, struct vm_area_struct *,
		unsigned long address, rmap_t flags);
void page_add_new_anon_rmap(struct page *, struct vm_area_struct *,
		unsigned long address);
void page_add_file_rmap(struct page *, struct vm_area_struct *,
		bool compound);
void page_remove_rmap(struct page *, struct vm_area_struct *,
		bool compound);

void hugepage_add_anon_rmap(struct page *, struct vm_area_struct *,
		unsigned long address, rmap_t flags);
void hugepage_add_new_anon_rmap(struct page *, struct vm_area_struct *,
		unsigned long address);

static inline void __page_dup_rmap(struct page *page, bool compound)
{
	atomic_inc(compound ? compound_mapcount_ptr(page) : &page->_mapcount);
}

static inline void page_dup_file_rmap(struct page *page, bool compound)
{
	__page_dup_rmap(page, compound);
}

/**
 * page_try_dup_anon_rmap - try duplicating a mapping of an already mapped
 *			    anonymous page
 * @page: the page to duplicate the mapping for
 * @compound: the page is mapped as compound or as a small page
 * @vma: the source vma
 *
 * The caller needs to hold the PT lock and the vma->vma_mm->write_protect_seq.
 *
 * Duplicating the mapping can only fail if the page may be pinned; device
 * private pages cannot get pinned and consequently this function cannot fail.
 *
 * If duplicating the mapping succeeds, the page has to be mapped R/O into
 * the parent and the child. It must *not* get mapped writable after this call.
 *
 * Returns 0 if duplicating the mapping succeeded. Returns -EBUSY otherwise.
 */
static inline int page_try_dup_anon_rmap(struct page *page, bool compound,
					 struct vm_area_struct *vma)
{
	VM_BUG_ON_PAGE(!PageAnon(page), page);

	/*
	 * No need to check+clear for already shared pages, including KSM
	 * pages.
	 */
	if (!PageAnonExclusive(page))
		goto dup;

	/*
	 * If this page may have been pinned by the parent process,
	 * don't allow to duplicate the mapping but instead require to e.g.,
	 * copy the page immediately for the child so that we'll always
	 * guarantee the pinned page won't be randomly replaced in the
	 * future on write faults.
	 */
	if (likely(!is_device_private_page(page) &&
	    unlikely(page_needs_cow_for_dma(vma, page))))
		return -EBUSY;

	ClearPageAnonExclusive(page);
	/*
	 * It's okay to share the anon page between both processes, mapping
	 * the page R/O into both processes.
	 */
dup:
	__page_dup_rmap(page, compound);
	return 0;
}

/**
 * page_try_share_anon_rmap - try marking an exclusive anonymous page possibly
 *			      shared to prepare for KSM or temporary unmapping
 * @page: the exclusive anonymous page to try marking possibly shared
 *
 * The caller needs to hold the PT lock and has to have the page table entry
 * cleared/invalidated.
 *
 * This is similar to page_try_dup_anon_rmap(), however, not used during fork()
 * to duplicate a mapping, but instead to prepare for KSM or temporarily
 * unmapping a page (swap, migration) via page_remove_rmap().
 *
 * Marking the page shared can only fail if the page may be pinned; device
 * private pages cannot get pinned and consequently this function cannot fail.
 *
 * Returns 0 if marking the page possibly shared succeeded. Returns -EBUSY
 * otherwise.
 */
static inline int page_try_share_anon_rmap(struct page *page)
{
	VM_BUG_ON_PAGE(!PageAnon(page) || !PageAnonExclusive(page), page);

	/* device private pages cannot get pinned via GUP. */
	if (unlikely(is_device_private_page(page))) {
		ClearPageAnonExclusive(page);
		return 0;
	}

	/*
	 * We have to make sure that when we clear PageAnonExclusive, that
	 * the page is not pinned and that concurrent GUP-fast won't succeed in
	 * concurrently pinning the page.
	 *
	 * Conceptually, PageAnonExclusive clearing consists of:
	 * (A1) Clear PTE
	 * (A2) Check if the page is pinned; back off if so.
	 * (A3) Clear PageAnonExclusive
	 * (A4) Restore PTE (optional, but certainly not writable)
	 *
	 * When clearing PageAnonExclusive, we cannot possibly map the page
	 * writable again, because anon pages that may be shared must never
	 * be writable. So in any case, if the PTE was writable it cannot
	 * be writable anymore afterwards and there would be a PTE change. Only
	 * if the PTE wasn't writable, there might not be a PTE change.
	 *
	 * Conceptually, GUP-fast pinning of an anon page consists of:
	 * (B1) Read the PTE
	 * (B2) FOLL_WRITE: check if the PTE is not writable; back off if so.
	 * (B3) Pin the mapped page
	 * (B4) Check if the PTE changed by re-reading it; back off if so.
	 * (B5) If the original PTE is not writable, check if
	 *	PageAnonExclusive is not set; back off if so.
	 *
	 * If the PTE was writable, we only have to make sure that GUP-fast
	 * observes a PTE change and properly backs off.
	 *
	 * If the PTE was not writable, we have to make sure that GUP-fast either
	 * detects a (temporary) PTE change or that PageAnonExclusive is cleared
	 * and properly backs off.
	 *
	 * Consequently, when clearing PageAnonExclusive(), we have to make
	 * sure that (A1), (A2)/(A3) and (A4) happen in the right memory
	 * order. In GUP-fast pinning code, we have to make sure that (B3),(B4)
	 * and (B5) happen in the right memory order.
	 *
	 * We assume that there might not be a memory barrier after
	 * clearing/invalidating the PTE (A1) and before restoring the PTE (A4),
	 * so we use explicit ones here.
	 */

	/* Paired with the memory barrier in try_grab_folio(). */
	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))
		smp_mb();

	if (unlikely(page_maybe_dma_pinned(page)))
		return -EBUSY;
	ClearPageAnonExclusive(page);

	/*
	 * This is conceptually a smp_wmb() paired with the smp_rmb() in
	 * gup_must_unshare().
	 */
	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))
		smp_mb__after_atomic();
	return 0;
}

/*
 * Called from mm/vmscan.c to handle paging out
 */
int folio_referenced(struct folio *, int is_locked,
			struct mem_cgroup *memcg, unsigned long *vm_flags);

void try_to_migrate(struct folio *folio, enum ttu_flags flags);
void try_to_unmap(struct folio *, enum ttu_flags flags);

int make_device_exclusive_range(struct mm_struct *mm, unsigned long start,
				unsigned long end, struct page **pages,
				void *arg);

/* Avoid racy checks */
#define PVMW_SYNC		(1 << 0)
/* Look for migration entries rather than present PTEs */
#define PVMW_MIGRATION		(1 << 1)

struct page_vma_mapped_walk {
	unsigned long pfn;
	unsigned long nr_pages;
	pgoff_t pgoff;
	struct vm_area_struct *vma;
	unsigned long address;
	pmd_t *pmd;
	pte_t *pte;
	spinlock_t *ptl;
	unsigned int flags;
};

#define DEFINE_PAGE_VMA_WALK(name, _page, _vma, _address, _flags)	\
	struct page_vma_mapped_walk name = {				\
		.pfn = page_to_pfn(_page),				\
		.nr_pages = compound_nr(_page),				\
		.pgoff = page_to_pgoff(_page),				\
		.vma = _vma,						\
		.address = _address,					\
		.flags = _flags,					\
	}

#define DEFINE_FOLIO_VMA_WALK(name, _folio, _vma, _address, _flags)	\
	struct page_vma_mapped_walk name = {				\
		.pfn = folio_pfn(_folio),				\
		.nr_pages = folio_nr_pages(_folio),			\
		.pgoff = folio_pgoff(_folio),				\
		.vma = _vma,						\
		.address = _address,					\
		.flags = _flags,					\
	}

static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
{
	/* HugeTLB pte is set to the relevant page table entry without pte_mapped. */
	if (pvmw->pte && !is_vm_hugetlb_page(pvmw->vma))
		pte_unmap(pvmw->pte);
	if (pvmw->ptl)
		spin_unlock(pvmw->ptl);
}

bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw);

/*
 * Used by swapoff to help locate where page is expected in vma.
 */
unsigned long page_address_in_vma(struct page *, struct vm_area_struct *);

/*
 * Cleans the PTEs of shared mappings.
 * (and since clean PTEs should also be readonly, write protects them too)
 *
 * returns the number of cleaned PTEs.
 */
int folio_mkclean(struct folio *);

int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
		      struct vm_area_struct *vma);

void remove_migration_ptes(struct folio *src, struct folio *dst, bool locked);

int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma);

/*
 * rmap_walk_control: To control rmap traversing for specific needs
 *
 * arg: passed to rmap_one() and invalid_vma()
 * try_lock: bail out if the rmap lock is contended
 * contended: indicate the rmap traversal bailed out due to lock contention
 * rmap_one: executed on each vma where page is mapped
 * done: for checking traversing termination condition
 * anon_lock: for getting anon_lock by optimized way rather than default
 * invalid_vma: for skipping uninterested vma
 */
struct rmap_walk_control {
	void *arg;
	bool try_lock;
	bool contended;
	/*
	 * Return false if page table scanning in rmap_walk should be stopped.
	 * Otherwise, return true.
	 */
	bool (*rmap_one)(struct folio *folio, struct vm_area_struct *vma,
					unsigned long addr, void *arg);
	int (*done)(struct folio *folio);
	struct anon_vma *(*anon_lock)(struct folio *folio,
				      struct rmap_walk_control *rwc);
	bool (*invalid_vma)(struct vm_area_struct *vma, void *arg);
};

void rmap_walk(struct folio *folio, struct rmap_walk_control *rwc);
void rmap_walk_locked(struct folio *folio, struct rmap_walk_control *rwc);
struct anon_vma *folio_lock_anon_vma_read(struct folio *folio,
					  struct rmap_walk_control *rwc);

#else	/* !CONFIG_MMU */

#define anon_vma_init()		do {} while (0)
#define anon_vma_prepare(vma)	(0)
#define anon_vma_link(vma)	do {} while (0)

static inline int folio_referenced(struct folio *folio, int is_locked,
				  struct mem_cgroup *memcg,
				  unsigned long *vm_flags)
{
	*vm_flags = 0;
	return 0;
}

static inline void try_to_unmap(struct folio *folio, enum ttu_flags flags)
{
}

static inline int folio_mkclean(struct folio *folio)
{
	return 0;
}
#endif	/* CONFIG_MMU */

static inline int page_mkclean(struct page *page)
{
	return folio_mkclean(page_folio(page));
}
#endif	/* _LINUX_RMAP_H */