1// SPDX-License-Identifier: GPL-2.0
2/*
3 * linux/fs/ext4/readpage.c
4 *
5 * Copyright (C) 2002, Linus Torvalds.
6 * Copyright (C) 2015, Google, Inc.
7 *
8 * This was originally taken from fs/mpage.c
9 *
10 * The ext4_mpage_readpages() function here is intended to
11 * replace mpage_readahead() in the general case, not just for
12 * encrypted files. It has some limitations (see below), where it
13 * will fall back to read_block_full_page(), but these limitations
14 * should only be hit when page_size != block_size.
15 *
16 * This will allow us to attach a callback function to support ext4
17 * encryption.
18 *
19 * If anything unusual happens, such as:
20 *
21 * - encountering a page which has buffers
22 * - encountering a page which has a non-hole after a hole
23 * - encountering a page with non-contiguous blocks
24 *
25 * then this code just gives up and calls the buffer_head-based read function.
26 * It does handle a page which has holes at the end - that is a common case:
27 * the end-of-file on blocksize < PAGE_SIZE setups.
28 *
29 */
30
31#include <linux/kernel.h>
32#include <linux/export.h>
33#include <linux/mm.h>
34#include <linux/kdev_t.h>
35#include <linux/gfp.h>
36#include <linux/bio.h>
37#include <linux/fs.h>
38#include <linux/buffer_head.h>
39#include <linux/blkdev.h>
40#include <linux/highmem.h>
41#include <linux/prefetch.h>
42#include <linux/mpage.h>
43#include <linux/writeback.h>
44#include <linux/backing-dev.h>
45#include <linux/pagevec.h>
46
47#include "ext4.h"
48
49#define NUM_PREALLOC_POST_READ_CTXS 128
50
51static struct kmem_cache *bio_post_read_ctx_cache;
52static mempool_t *bio_post_read_ctx_pool;
53
54/* postprocessing steps for read bios */
55enum bio_post_read_step {
56 STEP_INITIAL = 0,
57 STEP_DECRYPT,
58 STEP_VERITY,
59 STEP_MAX,
60};
61
62struct bio_post_read_ctx {
63 struct bio *bio;
64 struct work_struct work;
65 unsigned int cur_step;
66 unsigned int enabled_steps;
67};
68
69static void __read_end_io(struct bio *bio)
70{
71 struct folio_iter fi;
72
73 bio_for_each_folio_all(fi, bio)
74 folio_end_read(folio: fi.folio, success: bio->bi_status == 0);
75 if (bio->bi_private)
76 mempool_free(element: bio->bi_private, pool: bio_post_read_ctx_pool);
77 bio_put(bio);
78}
79
80static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
81
82static void decrypt_work(struct work_struct *work)
83{
84 struct bio_post_read_ctx *ctx =
85 container_of(work, struct bio_post_read_ctx, work);
86 struct bio *bio = ctx->bio;
87
88 if (fscrypt_decrypt_bio(bio))
89 bio_post_read_processing(ctx);
90 else
91 __read_end_io(bio);
92}
93
94static void verity_work(struct work_struct *work)
95{
96 struct bio_post_read_ctx *ctx =
97 container_of(work, struct bio_post_read_ctx, work);
98 struct bio *bio = ctx->bio;
99
100 /*
101 * fsverity_verify_bio() may call readahead() again, and although verity
102 * will be disabled for that, decryption may still be needed, causing
103 * another bio_post_read_ctx to be allocated. So to guarantee that
104 * mempool_alloc() never deadlocks we must free the current ctx first.
105 * This is safe because verity is the last post-read step.
106 */
107 BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
108 mempool_free(element: ctx, pool: bio_post_read_ctx_pool);
109 bio->bi_private = NULL;
110
111 fsverity_verify_bio(bio);
112
113 __read_end_io(bio);
114}
115
116static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
117{
118 /*
119 * We use different work queues for decryption and for verity because
120 * verity may require reading metadata pages that need decryption, and
121 * we shouldn't recurse to the same workqueue.
122 */
123 switch (++ctx->cur_step) {
124 case STEP_DECRYPT:
125 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
126 INIT_WORK(&ctx->work, decrypt_work);
127 fscrypt_enqueue_decrypt_work(&ctx->work);
128 return;
129 }
130 ctx->cur_step++;
131 fallthrough;
132 case STEP_VERITY:
133 if (ctx->enabled_steps & (1 << STEP_VERITY)) {
134 INIT_WORK(&ctx->work, verity_work);
135 fsverity_enqueue_verify_work(work: &ctx->work);
136 return;
137 }
138 ctx->cur_step++;
139 fallthrough;
140 default:
141 __read_end_io(bio: ctx->bio);
142 }
143}
144
145static bool bio_post_read_required(struct bio *bio)
146{
147 return bio->bi_private && !bio->bi_status;
148}
149
150/*
151 * I/O completion handler for multipage BIOs.
152 *
153 * The mpage code never puts partial pages into a BIO (except for end-of-file).
154 * If a page does not map to a contiguous run of blocks then it simply falls
155 * back to block_read_full_folio().
156 *
157 * Why is this? If a page's completion depends on a number of different BIOs
158 * which can complete in any order (or at the same time) then determining the
159 * status of that page is hard. See end_buffer_async_read() for the details.
160 * There is no point in duplicating all that complexity.
161 */
162static void mpage_end_io(struct bio *bio)
163{
164 if (bio_post_read_required(bio)) {
165 struct bio_post_read_ctx *ctx = bio->bi_private;
166
167 ctx->cur_step = STEP_INITIAL;
168 bio_post_read_processing(ctx);
169 return;
170 }
171 __read_end_io(bio);
172}
173
174static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
175{
176 return fsverity_active(inode) &&
177 idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
178}
179
180static void ext4_set_bio_post_read_ctx(struct bio *bio,
181 const struct inode *inode,
182 pgoff_t first_idx)
183{
184 unsigned int post_read_steps = 0;
185
186 if (fscrypt_inode_uses_fs_layer_crypto(inode))
187 post_read_steps |= 1 << STEP_DECRYPT;
188
189 if (ext4_need_verity(inode, idx: first_idx))
190 post_read_steps |= 1 << STEP_VERITY;
191
192 if (post_read_steps) {
193 /* Due to the mempool, this never fails. */
194 struct bio_post_read_ctx *ctx =
195 mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
196
197 ctx->bio = bio;
198 ctx->enabled_steps = post_read_steps;
199 bio->bi_private = ctx;
200 }
201}
202
203static inline loff_t ext4_readpage_limit(struct inode *inode)
204{
205 if (IS_ENABLED(CONFIG_FS_VERITY) && IS_VERITY(inode))
206 return inode->i_sb->s_maxbytes;
207
208 return i_size_read(inode);
209}
210
211int ext4_mpage_readpages(struct inode *inode,
212 struct readahead_control *rac, struct folio *folio)
213{
214 struct bio *bio = NULL;
215 sector_t last_block_in_bio = 0;
216
217 const unsigned blkbits = inode->i_blkbits;
218 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
219 const unsigned blocksize = 1 << blkbits;
220 sector_t next_block;
221 sector_t block_in_file;
222 sector_t last_block;
223 sector_t last_block_in_file;
224 sector_t first_block;
225 unsigned page_block;
226 struct block_device *bdev = inode->i_sb->s_bdev;
227 int length;
228 unsigned relative_block = 0;
229 struct ext4_map_blocks map;
230 unsigned int nr_pages, folio_pages;
231
232 map.m_pblk = 0;
233 map.m_lblk = 0;
234 map.m_len = 0;
235 map.m_flags = 0;
236
237 nr_pages = rac ? readahead_count(rac) : folio_nr_pages(folio);
238 for (; nr_pages; nr_pages -= folio_pages) {
239 int fully_mapped = 1;
240 unsigned int first_hole;
241 unsigned int blocks_per_folio;
242
243 if (rac)
244 folio = readahead_folio(ractl: rac);
245
246 folio_pages = folio_nr_pages(folio);
247 prefetchw(x: &folio->flags);
248
249 if (folio_buffers(folio))
250 goto confused;
251
252 blocks_per_folio = folio_size(folio) >> blkbits;
253 first_hole = blocks_per_folio;
254 block_in_file = next_block =
255 (sector_t)folio->index << (PAGE_SHIFT - blkbits);
256 last_block = block_in_file + nr_pages * blocks_per_page;
257 last_block_in_file = (ext4_readpage_limit(inode) +
258 blocksize - 1) >> blkbits;
259 if (last_block > last_block_in_file)
260 last_block = last_block_in_file;
261 page_block = 0;
262
263 /*
264 * Map blocks using the previous result first.
265 */
266 if ((map.m_flags & EXT4_MAP_MAPPED) &&
267 block_in_file > map.m_lblk &&
268 block_in_file < (map.m_lblk + map.m_len)) {
269 unsigned map_offset = block_in_file - map.m_lblk;
270 unsigned last = map.m_len - map_offset;
271
272 first_block = map.m_pblk + map_offset;
273 for (relative_block = 0; ; relative_block++) {
274 if (relative_block == last) {
275 /* needed? */
276 map.m_flags &= ~EXT4_MAP_MAPPED;
277 break;
278 }
279 if (page_block == blocks_per_folio)
280 break;
281 page_block++;
282 block_in_file++;
283 }
284 }
285
286 /*
287 * Then do more ext4_map_blocks() calls until we are
288 * done with this folio.
289 */
290 while (page_block < blocks_per_folio) {
291 if (block_in_file < last_block) {
292 map.m_lblk = block_in_file;
293 map.m_len = last_block - block_in_file;
294
295 if (ext4_map_blocks(NULL, inode, map: &map, flags: 0) < 0) {
296 set_error_page:
297 folio_zero_segment(folio, start: 0,
298 xend: folio_size(folio));
299 folio_unlock(folio);
300 goto next_page;
301 }
302 }
303 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
304 fully_mapped = 0;
305 if (first_hole == blocks_per_folio)
306 first_hole = page_block;
307 page_block++;
308 block_in_file++;
309 continue;
310 }
311 if (first_hole != blocks_per_folio)
312 goto confused; /* hole -> non-hole */
313
314 /* Contiguous blocks? */
315 if (!page_block)
316 first_block = map.m_pblk;
317 else if (first_block + page_block != map.m_pblk)
318 goto confused;
319 for (relative_block = 0; ; relative_block++) {
320 if (relative_block == map.m_len) {
321 /* needed? */
322 map.m_flags &= ~EXT4_MAP_MAPPED;
323 break;
324 } else if (page_block == blocks_per_folio)
325 break;
326 page_block++;
327 block_in_file++;
328 }
329 }
330 if (first_hole != blocks_per_folio) {
331 folio_zero_segment(folio, start: first_hole << blkbits,
332 xend: folio_size(folio));
333 if (first_hole == 0) {
334 if (ext4_need_verity(inode, idx: folio->index) &&
335 !fsverity_verify_folio(folio))
336 goto set_error_page;
337 folio_end_read(folio, success: true);
338 continue;
339 }
340 } else if (fully_mapped) {
341 folio_set_mappedtodisk(folio);
342 }
343
344 /*
345 * This folio will go to BIO. Do we need to send this
346 * BIO off first?
347 */
348 if (bio && (last_block_in_bio != first_block - 1 ||
349 !fscrypt_mergeable_bio(bio, inode, next_lblk: next_block))) {
350 submit_and_realloc:
351 submit_bio(bio);
352 bio = NULL;
353 }
354 if (bio == NULL) {
355 /*
356 * bio_alloc will _always_ be able to allocate a bio if
357 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
358 */
359 bio = bio_alloc(bdev, nr_vecs: bio_max_segs(nr_segs: nr_pages),
360 opf: REQ_OP_READ, GFP_KERNEL);
361 fscrypt_set_bio_crypt_ctx(bio, inode, first_lblk: next_block,
362 GFP_KERNEL);
363 ext4_set_bio_post_read_ctx(bio, inode, first_idx: folio->index);
364 bio->bi_iter.bi_sector = first_block << (blkbits - 9);
365 bio->bi_end_io = mpage_end_io;
366 if (rac)
367 bio->bi_opf |= REQ_RAHEAD;
368 }
369
370 length = first_hole << blkbits;
371 if (!bio_add_folio(bio, folio, len: length, off: 0))
372 goto submit_and_realloc;
373
374 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
375 (relative_block == map.m_len)) ||
376 (first_hole != blocks_per_folio)) {
377 submit_bio(bio);
378 bio = NULL;
379 } else
380 last_block_in_bio = first_block + blocks_per_folio - 1;
381 continue;
382 confused:
383 if (bio) {
384 submit_bio(bio);
385 bio = NULL;
386 }
387 if (!folio_test_uptodate(folio))
388 block_read_full_folio(folio, ext4_get_block);
389 else
390 folio_unlock(folio);
391next_page:
392 ; /* A label shall be followed by a statement until C23 */
393 }
394 if (bio)
395 submit_bio(bio);
396 return 0;
397}
398
399int __init ext4_init_post_read_processing(void)
400{
401 bio_post_read_ctx_cache = KMEM_CACHE(bio_post_read_ctx, SLAB_RECLAIM_ACCOUNT);
402
403 if (!bio_post_read_ctx_cache)
404 goto fail;
405 bio_post_read_ctx_pool =
406 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
407 bio_post_read_ctx_cache);
408 if (!bio_post_read_ctx_pool)
409 goto fail_free_cache;
410 return 0;
411
412fail_free_cache:
413 kmem_cache_destroy(s: bio_post_read_ctx_cache);
414fail:
415 return -ENOMEM;
416}
417
418void ext4_exit_post_read_processing(void)
419{
420 mempool_destroy(pool: bio_post_read_ctx_pool);
421 kmem_cache_destroy(s: bio_post_read_ctx_cache);
422}
423

source code of linux/fs/ext4/readpage.c