aboutsummaryrefslogtreecommitdiff
path: root/fs/ext4/readpage.c
blob: f014c5e473a9d228d7c3e66ef0214768725a0540 (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
// SPDX-License-Identifier: GPL-2.0
/*
 * linux/fs/ext4/readpage.c
 *
 * Copyright (C) 2002, Linus Torvalds.
 * Copyright (C) 2015, Google, Inc.
 *
 * This was originally taken from fs/mpage.c
 *
 * The ext4_mpage_readpages() function here is intended to
 * replace mpage_readahead() in the general case, not just for
 * encrypted files.  It has some limitations (see below), where it
 * will fall back to read_block_full_page(), but these limitations
 * should only be hit when page_size != block_size.
 *
 * This will allow us to attach a callback function to support ext4
 * encryption.
 *
 * If anything unusual happens, such as:
 *
 * - encountering a page which has buffers
 * - encountering a page which has a non-hole after a hole
 * - encountering a page with non-contiguous blocks
 *
 * then this code just gives up and calls the buffer_head-based read function.
 * It does handle a page which has holes at the end - that is a common case:
 * the end-of-file on blocksize < PAGE_SIZE setups.
 *
 */

#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/kdev_t.h>
#include <linux/gfp.h>
#include <linux/bio.h>
#include <linux/fs.h>
#include <linux/buffer_head.h>
#include <linux/blkdev.h>
#include <linux/highmem.h>
#include <linux/prefetch.h>
#include <linux/mpage.h>
#include <linux/writeback.h>
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
#include <linux/cleancache.h>

#include "ext4.h"

#define NUM_PREALLOC_POST_READ_CTXS	128

static struct kmem_cache *bio_post_read_ctx_cache;
static mempool_t *bio_post_read_ctx_pool;

/* postprocessing steps for read bios */
enum bio_post_read_step {
	STEP_INITIAL = 0,
	STEP_DECRYPT,
	STEP_VERITY,
	STEP_MAX,
};

struct bio_post_read_ctx {
	struct bio *bio;
	struct work_struct work;
	unsigned int cur_step;
	unsigned int enabled_steps;
};

static void __read_end_io(struct bio *bio)
{
	struct page *page;
	struct bio_vec *bv;
	struct bvec_iter_all iter_all;

	bio_for_each_segment_all(bv, bio, iter_all) {
		page = bv->bv_page;

		/* PG_error was set if any post_read step failed */
		if (bio->bi_status || PageError(page)) {
			ClearPageUptodate(page);
			/* will re-read again later */
			ClearPageError(page);
		} else {
			SetPageUptodate(page);
		}
		unlock_page(page);
	}
	if (bio->bi_private)
		mempool_free(bio->bi_private, bio_post_read_ctx_pool);
	bio_put(bio);
}

static void bio_post_read_processing(struct bio_post_read_ctx *ctx);

static void decrypt_work(struct work_struct *work)
{
	struct bio_post_read_ctx *ctx =
		container_of(work, struct bio_post_read_ctx, work);

	fscrypt_decrypt_bio(ctx->bio);

	bio_post_read_processing(ctx);
}

static void verity_work(struct work_struct *work)
{
	struct bio_post_read_ctx *ctx =
		container_of(work, struct bio_post_read_ctx, work);
	struct bio *bio = ctx->bio;

	/*
	 * fsverity_verify_bio() may call readpages() again, and although verity
	 * will be disabled for that, decryption may still be needed, causing
	 * another bio_post_read_ctx to be allocated.  So to guarantee that
	 * mempool_alloc() never deadlocks we must free the current ctx first.
	 * This is safe because verity is the last post-read step.
	 */
	BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
	mempool_free(ctx, bio_post_read_ctx_pool);
	bio->bi_private = NULL;

	fsverity_verify_bio(bio);

	__read_end_io(bio);
}

static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
{
	/*
	 * We use different work queues for decryption and for verity because
	 * verity may require reading metadata pages that need decryption, and
	 * we shouldn't recurse to the same workqueue.
	 */
	switch (++ctx->cur_step) {
	case STEP_DECRYPT:
		if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
			INIT_WORK(&ctx->work, decrypt_work);
			fscrypt_enqueue_decrypt_work(&ctx->work);
			return;
		}
		ctx->cur_step++;
		fallthrough;
	case STEP_VERITY:
		if (ctx->enabled_steps & (1 << STEP_VERITY)) {
			INIT_WORK(&ctx->work, verity_work);
			fsverity_enqueue_verify_work(&ctx->work);
			return;
		}
		ctx->cur_step++;
		fallthrough;
	default:
		__read_end_io(ctx->bio);
	}
}

static bool bio_post_read_required(struct bio *bio)
{
	return bio->bi_private && !bio->bi_status;
}

/*
 * I/O completion handler for multipage BIOs.
 *
 * The mpage code never puts partial pages into a BIO (except for end-of-file).
 * If a page does not map to a contiguous run of blocks then it simply falls
 * back to block_read_full_page().
 *
 * Why is this?  If a page's completion depends on a number of different BIOs
 * which can complete in any order (or at the same time) then determining the
 * status of that page is hard.  See end_buffer_async_read() for the details.
 * There is no point in duplicating all that complexity.
 */
static void mpage_end_io(struct bio *bio)
{
	if (bio_post_read_required(bio)) {
		struct bio_post_read_ctx *ctx = bio->bi_private;

		ctx->cur_step = STEP_INITIAL;
		bio_post_read_processing(ctx);
		return;
	}
	__read_end_io(bio);
}

static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
{
	return fsverity_active(inode) &&
	       idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
}

static void ext4_set_bio_post_read_ctx(struct bio *bio,
				       const struct inode *inode,
				       pgoff_t first_idx)
{
	unsigned int post_read_steps = 0;

	if (fscrypt_inode_uses_fs_layer_crypto(inode))
		post_read_steps |= 1 << STEP_DECRYPT;

	if (ext4_need_verity(inode, first_idx))
		post_read_steps |= 1 << STEP_VERITY;

	if (post_read_steps) {
		/* Due to the mempool, this never fails. */
		struct bio_post_read_ctx *ctx =
			mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);

		ctx->bio = bio;
		ctx->enabled_steps = post_read_steps;
		bio->bi_private = ctx;
	}
}

static inline loff_t ext4_readpage_limit(struct inode *inode)
{
	if (IS_ENABLED(CONFIG_FS_VERITY) &&
	    (IS_VERITY(inode) || ext4_verity_in_progress(inode)))
		return inode->i_sb->s_maxbytes;

	return i_size_read(inode);
}

int ext4_mpage_readpages(struct inode *inode,
		struct readahead_control *rac, struct page *page)
{
	struct bio *bio = NULL;
	sector_t last_block_in_bio = 0;

	const unsigned blkbits = inode->i_blkbits;
	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
	const unsigned blocksize = 1 << blkbits;
	sector_t next_block;
	sector_t block_in_file;
	sector_t last_block;
	sector_t last_block_in_file;
	sector_t blocks[MAX_BUF_PER_PAGE];
	unsigned page_block;
	struct block_device *bdev = inode->i_sb->s_bdev;
	int length;
	unsigned relative_block = 0;
	struct ext4_map_blocks map;
	unsigned int nr_pages = rac ? readahead_count(rac) : 1;

	map.m_pblk = 0;
	map.m_lblk = 0;
	map.m_len = 0;
	map.m_flags = 0;

	for (; nr_pages; nr_pages--) {
		int fully_mapped = 1;
		unsigned first_hole = blocks_per_page;

		if (rac) {
			page = readahead_page(rac);
			prefetchw(&page->flags);
		}

		if (page_has_buffers(page))
			goto confused;

		block_in_file = next_block =
			(sector_t)page->index << (PAGE_SHIFT - blkbits);
		last_block = block_in_file + nr_pages * blocks_per_page;
		last_block_in_file = (ext4_readpage_limit(inode) +
				      blocksize - 1) >> blkbits;
		if (last_block > last_block_in_file)
			last_block = last_block_in_file;
		page_block = 0;

		/*
		 * Map blocks using the previous result first.
		 */
		if ((map.m_flags & EXT4_MAP_MAPPED) &&
		    block_in_file > map.m_lblk &&
		    block_in_file < (map.m_lblk + map.m_len)) {
			unsigned map_offset = block_in_file - map.m_lblk;
			unsigned last = map.m_len - map_offset;

			for (relative_block = 0; ; relative_block++) {
				if (relative_block == last) {
					/* needed? */
					map.m_flags &= ~EXT4_MAP_MAPPED;
					break;
				}
				if (page_block == blocks_per_page)
					break;
				blocks[page_block] = map.m_pblk + map_offset +
					relative_block;
				page_block++;
				block_in_file++;
			}
		}

		/*
		 * Then do more ext4_map_blocks() calls until we are
		 * done with this page.
		 */
		while (page_block < blocks_per_page) {
			if (block_in_file < last_block) {
				map.m_lblk = block_in_file;
				map.m_len = last_block - block_in_file;

				if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
				set_error_page:
					SetPageError(page);
					zero_user_segment(page, 0,
							  PAGE_SIZE);
					unlock_page(page);
					goto next_page;
				}
			}
			if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
				fully_mapped = 0;
				if (first_hole == blocks_per_page)
					first_hole = page_block;
				page_block++;
				block_in_file++;
				continue;
			}
			if (first_hole != blocks_per_page)
				goto confused;		/* hole -> non-hole */

			/* Contiguous blocks? */
			if (page_block && blocks[page_block-1] != map.m_pblk-1)
				goto confused;
			for (relative_block = 0; ; relative_block++) {
				if (relative_block == map.m_len) {
					/* needed? */
					map.m_flags &= ~EXT4_MAP_MAPPED;
					break;
				} else if (page_block == blocks_per_page)
					break;
				blocks[page_block] = map.m_pblk+relative_block;
				page_block++;
				block_in_file++;
			}
		}
		if (first_hole != blocks_per_page) {
			zero_user_segment(page, first_hole << blkbits,
					  PAGE_SIZE);
			if (first_hole == 0) {
				if (ext4_need_verity(inode, page->index) &&
				    !fsverity_verify_page(page))
					goto set_error_page;
				SetPageUptodate(page);
				unlock_page(page);
				goto next_page;
			}
		} else if (fully_mapped) {
			SetPageMappedToDisk(page);
		}
		if (fully_mapped && blocks_per_page == 1 &&
		    !PageUptodate(page) && cleancache_get_page(page) == 0) {
			SetPageUptodate(page);
			goto confused;
		}

		/*
		 * This page will go to BIO.  Do we need to send this
		 * BIO off first?
		 */
		if (bio && (last_block_in_bio != blocks[0] - 1 ||
			    !fscrypt_mergeable_bio(bio, inode, next_block))) {
		submit_and_realloc:
			submit_bio(bio);
			bio = NULL;
		}
		if (bio == NULL) {
			/*
			 * bio_alloc will _always_ be able to allocate a bio if
			 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
			 */
			bio = bio_alloc(GFP_KERNEL,
				min_t(int, nr_pages, BIO_MAX_PAGES));
			fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
						  GFP_KERNEL);
			ext4_set_bio_post_read_ctx(bio, inode, page->index);
			bio_set_dev(bio, bdev);
			bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
			bio->bi_end_io = mpage_end_io;
			bio_set_op_attrs(bio, REQ_OP_READ,
						rac ? REQ_RAHEAD : 0);
		}

		length = first_hole << blkbits;
		if (bio_add_page(bio, page, length, 0) < length)
			goto submit_and_realloc;

		if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
		     (relative_block == map.m_len)) ||
		    (first_hole != blocks_per_page)) {
			submit_bio(bio);
			bio = NULL;
		} else
			last_block_in_bio = blocks[blocks_per_page - 1];
		goto next_page;
	confused:
		if (bio) {
			submit_bio(bio);
			bio = NULL;
		}
		if (!PageUptodate(page))
			block_read_full_page(page, ext4_get_block);
		else
			unlock_page(page);
	next_page:
		if (rac)
			put_page(page);
	}
	if (bio)
		submit_bio(bio);
	return 0;
}

int __init ext4_init_post_read_processing(void)
{
	bio_post_read_ctx_cache =
		kmem_cache_create("ext4_bio_post_read_ctx",
				  sizeof(struct bio_post_read_ctx), 0, 0, NULL);
	if (!bio_post_read_ctx_cache)
		goto fail;
	bio_post_read_ctx_pool =
		mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
					 bio_post_read_ctx_cache);
	if (!bio_post_read_ctx_pool)
		goto fail_free_cache;
	return 0;

fail_free_cache:
	kmem_cache_destroy(bio_post_read_ctx_cache);
fail:
	return -ENOMEM;
}

void ext4_exit_post_read_processing(void)
{
	mempool_destroy(bio_post_read_ctx_pool);
	kmem_cache_destroy(bio_post_read_ctx_cache);
}