aboutsummaryrefslogtreecommitdiff
path: root/mm/mapping_dirty_helpers.c
blob: ea734f248fce00db7a863a74c4fe3a822d21af92 (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
// SPDX-License-Identifier: GPL-2.0
#include <linux/pagewalk.h>
#include <linux/hugetlb.h>
#include <linux/bitops.h>
#include <linux/mmu_notifier.h>
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>

/**
 * struct wp_walk - Private struct for pagetable walk callbacks
 * @range: Range for mmu notifiers
 * @tlbflush_start: Address of first modified pte
 * @tlbflush_end: Address of last modified pte + 1
 * @total: Total number of modified ptes
 */
struct wp_walk {
	struct mmu_notifier_range range;
	unsigned long tlbflush_start;
	unsigned long tlbflush_end;
	unsigned long total;
};

/**
 * wp_pte - Write-protect a pte
 * @pte: Pointer to the pte
 * @addr: The start of protecting virtual address
 * @end: The end of protecting virtual address
 * @walk: pagetable walk callback argument
 *
 * The function write-protects a pte and records the range in
 * virtual address space of touched ptes for efficient range TLB flushes.
 */
static int wp_pte(pte_t *pte, unsigned long addr, unsigned long end,
		  struct mm_walk *walk)
{
	struct wp_walk *wpwalk = walk->private;
	pte_t ptent = *pte;

	if (pte_write(ptent)) {
		pte_t old_pte = ptep_modify_prot_start(walk->vma, addr, pte);

		ptent = pte_wrprotect(old_pte);
		ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent);
		wpwalk->total++;
		wpwalk->tlbflush_start = min(wpwalk->tlbflush_start, addr);
		wpwalk->tlbflush_end = max(wpwalk->tlbflush_end,
					   addr + PAGE_SIZE);
	}

	return 0;
}

/**
 * struct clean_walk - Private struct for the clean_record_pte function.
 * @base: struct wp_walk we derive from
 * @bitmap_pgoff: Address_space Page offset of the first bit in @bitmap
 * @bitmap: Bitmap with one bit for each page offset in the address_space range
 * covered.
 * @start: Address_space page offset of first modified pte relative
 * to @bitmap_pgoff
 * @end: Address_space page offset of last modified pte relative
 * to @bitmap_pgoff
 */
struct clean_walk {
	struct wp_walk base;
	pgoff_t bitmap_pgoff;
	unsigned long *bitmap;
	pgoff_t start;
	pgoff_t end;
};

#define to_clean_walk(_wpwalk) container_of(_wpwalk, struct clean_walk, base)

/**
 * clean_record_pte - Clean a pte and record its address space offset in a
 * bitmap
 * @pte: Pointer to the pte
 * @addr: The start of virtual address to be clean
 * @end: The end of virtual address to be clean
 * @walk: pagetable walk callback argument
 *
 * The function cleans a pte and records the range in
 * virtual address space of touched ptes for efficient TLB flushes.
 * It also records dirty ptes in a bitmap representing page offsets
 * in the address_space, as well as the first and last of the bits
 * touched.
 */
static int clean_record_pte(pte_t *pte, unsigned long addr,
			    unsigned long end, struct mm_walk *walk)
{
	struct wp_walk *wpwalk = walk->private;
	struct clean_walk *cwalk = to_clean_walk(wpwalk);
	pte_t ptent = *pte;

	if (pte_dirty(ptent)) {
		pgoff_t pgoff = ((addr - walk->vma->vm_start) >> PAGE_SHIFT) +
			walk->vma->vm_pgoff - cwalk->bitmap_pgoff;
		pte_t old_pte = ptep_modify_prot_start(walk->vma, addr, pte);

		ptent = pte_mkclean(old_pte);
		ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent);

		wpwalk->total++;
		wpwalk->tlbflush_start = min(wpwalk->tlbflush_start, addr);
		wpwalk->tlbflush_end = max(wpwalk->tlbflush_end,
					   addr + PAGE_SIZE);

		__set_bit(pgoff, cwalk->bitmap);
		cwalk->start = min(cwalk->start, pgoff);
		cwalk->end = max(cwalk->end, pgoff + 1);
	}

	return 0;
}

/*
 * wp_clean_pmd_entry - The pagewalk pmd callback.
 *
 * Dirty-tracking should take place on the PTE level, so
 * WARN() if encountering a dirty huge pmd.
 * Furthermore, never split huge pmds, since that currently
 * causes dirty info loss. The pagefault handler should do
 * that if needed.
 */
static int wp_clean_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long end,
			      struct mm_walk *walk)
{
	pmd_t pmdval = pmd_read_atomic(pmd);

	if (!pmd_trans_unstable(&pmdval))
		return 0;

	if (pmd_none(pmdval)) {
		walk->action = ACTION_AGAIN;
		return 0;
	}

	/* Huge pmd, present or migrated */
	walk->action = ACTION_CONTINUE;
	if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval))
		WARN_ON(pmd_write(pmdval) || pmd_dirty(pmdval));

	return 0;
}

/*
 * wp_clean_pud_entry - The pagewalk pud callback.
 *
 * Dirty-tracking should take place on the PTE level, so
 * WARN() if encountering a dirty huge puds.
 * Furthermore, never split huge puds, since that currently
 * causes dirty info loss. The pagefault handler should do
 * that if needed.
 */
static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end,
			      struct mm_walk *walk)
{
	pud_t pudval = READ_ONCE(*pud);

	if (!pud_trans_unstable(&pudval))
		return 0;

	if (pud_none(pudval)) {
		walk->action = ACTION_AGAIN;
		return 0;
	}

#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
	/* Huge pud */
	walk->action = ACTION_CONTINUE;
	if (pud_trans_huge(pudval) || pud_devmap(pudval))
		WARN_ON(pud_write(pudval) || pud_dirty(pudval));
#endif

	return 0;
}

/*
 * wp_clean_pre_vma - The pagewalk pre_vma callback.
 *
 * The pre_vma callback performs the cache flush, stages the tlb flush
 * and calls the necessary mmu notifiers.
 */
static int wp_clean_pre_vma(unsigned long start, unsigned long end,
			    struct mm_walk *walk)
{
	struct wp_walk *wpwalk = walk->private;

	wpwalk->tlbflush_start = end;
	wpwalk->tlbflush_end = start;

	mmu_notifier_range_init(&wpwalk->range, MMU_NOTIFY_PROTECTION_PAGE, 0,
				walk->vma, walk->mm, start, end);
	mmu_notifier_invalidate_range_start(&wpwalk->range);
	flush_cache_range(walk->vma, start, end);

	/*
	 * We're not using tlb_gather_mmu() since typically
	 * only a small subrange of PTEs are affected, whereas
	 * tlb_gather_mmu() records the full range.
	 */
	inc_tlb_flush_pending(walk->mm);

	return 0;
}

/*
 * wp_clean_post_vma - The pagewalk post_vma callback.
 *
 * The post_vma callback performs the tlb flush and calls necessary mmu
 * notifiers.
 */
static void wp_clean_post_vma(struct mm_walk *walk)
{
	struct wp_walk *wpwalk = walk->private;

	if (mm_tlb_flush_nested(walk->mm))
		flush_tlb_range(walk->vma, wpwalk->range.start,
				wpwalk->range.end);
	else if (wpwalk->tlbflush_end > wpwalk->tlbflush_start)
		flush_tlb_range(walk->vma, wpwalk->tlbflush_start,
				wpwalk->tlbflush_end);

	mmu_notifier_invalidate_range_end(&wpwalk->range);
	dec_tlb_flush_pending(walk->mm);
}

/*
 * wp_clean_test_walk - The pagewalk test_walk callback.
 *
 * Won't perform dirty-tracking on COW, read-only or HUGETLB vmas.
 */
static int wp_clean_test_walk(unsigned long start, unsigned long end,
			      struct mm_walk *walk)
{
	unsigned long vm_flags = READ_ONCE(walk->vma->vm_flags);

	/* Skip non-applicable VMAs */
	if ((vm_flags & (VM_SHARED | VM_MAYWRITE | VM_HUGETLB)) !=
	    (VM_SHARED | VM_MAYWRITE))
		return 1;

	return 0;
}

static const struct mm_walk_ops clean_walk_ops = {
	.pte_entry = clean_record_pte,
	.pmd_entry = wp_clean_pmd_entry,
	.pud_entry = wp_clean_pud_entry,
	.test_walk = wp_clean_test_walk,
	.pre_vma = wp_clean_pre_vma,
	.post_vma = wp_clean_post_vma
};

static const struct mm_walk_ops wp_walk_ops = {
	.pte_entry = wp_pte,
	.pmd_entry = wp_clean_pmd_entry,
	.pud_entry = wp_clean_pud_entry,
	.test_walk = wp_clean_test_walk,
	.pre_vma = wp_clean_pre_vma,
	.post_vma = wp_clean_post_vma
};

/**
 * wp_shared_mapping_range - Write-protect all ptes in an address space range
 * @mapping: The address_space we want to write protect
 * @first_index: The first page offset in the range
 * @nr: Number of incremental page offsets to cover
 *
 * Note: This function currently skips transhuge page-table entries, since
 * it's intended for dirty-tracking on the PTE level. It will warn on
 * encountering transhuge write-enabled entries, though, and can easily be
 * extended to handle them as well.
 *
 * Return: The number of ptes actually write-protected. Note that
 * already write-protected ptes are not counted.
 */
unsigned long wp_shared_mapping_range(struct address_space *mapping,
				      pgoff_t first_index, pgoff_t nr)
{
	struct wp_walk wpwalk = { .total = 0 };

	i_mmap_lock_read(mapping);
	WARN_ON(walk_page_mapping(mapping, first_index, nr, &wp_walk_ops,
				  &wpwalk));
	i_mmap_unlock_read(mapping);

	return wpwalk.total;
}
EXPORT_SYMBOL_GPL(wp_shared_mapping_range);

/**
 * clean_record_shared_mapping_range - Clean and record all ptes in an
 * address space range
 * @mapping: The address_space we want to clean
 * @first_index: The first page offset in the range
 * @nr: Number of incremental page offsets to cover
 * @bitmap_pgoff: The page offset of the first bit in @bitmap
 * @bitmap: Pointer to a bitmap of at least @nr bits. The bitmap needs to
 * cover the whole range @first_index..@first_index + @nr.
 * @start: Pointer to number of the first set bit in @bitmap.
 * is modified as new bits are set by the function.
 * @end: Pointer to the number of the last set bit in @bitmap.
 * none set. The value is modified as new bits are set by the function.
 *
 * Note: When this function returns there is no guarantee that a CPU has
 * not already dirtied new ptes. However it will not clean any ptes not
 * reported in the bitmap. The guarantees are as follows:
 * a) All ptes dirty when the function starts executing will end up recorded
 *    in the bitmap.
 * b) All ptes dirtied after that will either remain dirty, be recorded in the
 *    bitmap or both.
 *
 * If a caller needs to make sure all dirty ptes are picked up and none
 * additional are added, it first needs to write-protect the address-space
 * range and make sure new writers are blocked in page_mkwrite() or
 * pfn_mkwrite(). And then after a TLB flush following the write-protection
 * pick up all dirty bits.
 *
 * This function currently skips transhuge page-table entries, since
 * it's intended for dirty-tracking on the PTE level. It will warn on
 * encountering transhuge dirty entries, though, and can easily be extended
 * to handle them as well.
 *
 * Return: The number of dirty ptes actually cleaned.
 */
unsigned long clean_record_shared_mapping_range(struct address_space *mapping,
						pgoff_t first_index, pgoff_t nr,
						pgoff_t bitmap_pgoff,
						unsigned long *bitmap,
						pgoff_t *start,
						pgoff_t *end)
{
	bool none_set = (*start >= *end);
	struct clean_walk cwalk = {
		.base = { .total = 0 },
		.bitmap_pgoff = bitmap_pgoff,
		.bitmap = bitmap,
		.start = none_set ? nr : *start,
		.end = none_set ? 0 : *end,
	};

	i_mmap_lock_read(mapping);
	WARN_ON(walk_page_mapping(mapping, first_index, nr, &clean_walk_ops,
				  &cwalk.base));
	i_mmap_unlock_read(mapping);

	*start = cwalk.start;
	*end = cwalk.end;

	return cwalk.base.total;
}
EXPORT_SYMBOL_GPL(clean_record_shared_mapping_range);