1 // SPDX-License-Identifier: GPL-2.0
3 * linux/fs/ext4/readpage.c
5 * Copyright (C) 2002, Linus Torvalds.
6 * Copyright (C) 2015, Google, Inc.
8 * This was originally taken from fs/mpage.c
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.
16 * This will allow us to attach a callback function to support ext4
19 * If anything unusual happens, such as:
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
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.
31 #include <linux/kernel.h>
32 #include <linux/export.h>
34 #include <linux/kdev_t.h>
35 #include <linux/gfp.h>
36 #include <linux/bio.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 #include <linux/cleancache.h>
50 #define NUM_PREALLOC_POST_READ_CTXS 128
52 static struct kmem_cache *bio_post_read_ctx_cache;
53 static mempool_t *bio_post_read_ctx_pool;
55 /* postprocessing steps for read bios */
56 enum bio_post_read_step {
63 struct bio_post_read_ctx {
65 struct work_struct work;
66 unsigned int cur_step;
67 unsigned int enabled_steps;
70 static void __read_end_io(struct bio *bio)
74 struct bvec_iter_all iter_all;
76 bio_for_each_segment_all(bv, bio, iter_all) {
79 /* PG_error was set if any post_read step failed */
80 if (bio->bi_status || PageError(page)) {
81 ClearPageUptodate(page);
82 /* will re-read again later */
85 SetPageUptodate(page);
90 mempool_free(bio->bi_private, bio_post_read_ctx_pool);
94 static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
96 static void decrypt_work(struct work_struct *work)
98 struct bio_post_read_ctx *ctx =
99 container_of(work, struct bio_post_read_ctx, work);
101 fscrypt_decrypt_bio(ctx->bio);
103 bio_post_read_processing(ctx);
106 static void verity_work(struct work_struct *work)
108 struct bio_post_read_ctx *ctx =
109 container_of(work, struct bio_post_read_ctx, work);
110 struct bio *bio = ctx->bio;
113 * fsverity_verify_bio() may call readpages() again, and although verity
114 * will be disabled for that, decryption may still be needed, causing
115 * another bio_post_read_ctx to be allocated. So to guarantee that
116 * mempool_alloc() never deadlocks we must free the current ctx first.
117 * This is safe because verity is the last post-read step.
119 BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
120 mempool_free(ctx, bio_post_read_ctx_pool);
121 bio->bi_private = NULL;
123 fsverity_verify_bio(bio);
128 static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
131 * We use different work queues for decryption and for verity because
132 * verity may require reading metadata pages that need decryption, and
133 * we shouldn't recurse to the same workqueue.
135 switch (++ctx->cur_step) {
137 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
138 INIT_WORK(&ctx->work, decrypt_work);
139 fscrypt_enqueue_decrypt_work(&ctx->work);
145 if (ctx->enabled_steps & (1 << STEP_VERITY)) {
146 INIT_WORK(&ctx->work, verity_work);
147 fsverity_enqueue_verify_work(&ctx->work);
153 __read_end_io(ctx->bio);
157 static bool bio_post_read_required(struct bio *bio)
159 return bio->bi_private && !bio->bi_status;
163 * I/O completion handler for multipage BIOs.
165 * The mpage code never puts partial pages into a BIO (except for end-of-file).
166 * If a page does not map to a contiguous run of blocks then it simply falls
167 * back to block_read_full_page().
169 * Why is this? If a page's completion depends on a number of different BIOs
170 * which can complete in any order (or at the same time) then determining the
171 * status of that page is hard. See end_buffer_async_read() for the details.
172 * There is no point in duplicating all that complexity.
174 static void mpage_end_io(struct bio *bio)
176 if (bio_post_read_required(bio)) {
177 struct bio_post_read_ctx *ctx = bio->bi_private;
179 ctx->cur_step = STEP_INITIAL;
180 bio_post_read_processing(ctx);
186 static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
188 return fsverity_active(inode) &&
189 idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
192 static void ext4_set_bio_post_read_ctx(struct bio *bio,
193 const struct inode *inode,
196 unsigned int post_read_steps = 0;
198 if (fscrypt_inode_uses_fs_layer_crypto(inode))
199 post_read_steps |= 1 << STEP_DECRYPT;
201 if (ext4_need_verity(inode, first_idx))
202 post_read_steps |= 1 << STEP_VERITY;
204 if (post_read_steps) {
205 /* Due to the mempool, this never fails. */
206 struct bio_post_read_ctx *ctx =
207 mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
210 ctx->enabled_steps = post_read_steps;
211 bio->bi_private = ctx;
215 static inline loff_t ext4_readpage_limit(struct inode *inode)
217 if (IS_ENABLED(CONFIG_FS_VERITY) &&
218 (IS_VERITY(inode) || ext4_verity_in_progress(inode)))
219 return inode->i_sb->s_maxbytes;
221 return i_size_read(inode);
224 int ext4_mpage_readpages(struct inode *inode,
225 struct readahead_control *rac, struct page *page)
227 struct bio *bio = NULL;
228 sector_t last_block_in_bio = 0;
230 const unsigned blkbits = inode->i_blkbits;
231 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
232 const unsigned blocksize = 1 << blkbits;
234 sector_t block_in_file;
236 sector_t last_block_in_file;
237 sector_t blocks[MAX_BUF_PER_PAGE];
239 struct block_device *bdev = inode->i_sb->s_bdev;
241 unsigned relative_block = 0;
242 struct ext4_map_blocks map;
243 unsigned int nr_pages = rac ? readahead_count(rac) : 1;
250 for (; nr_pages; nr_pages--) {
251 int fully_mapped = 1;
252 unsigned first_hole = blocks_per_page;
255 page = readahead_page(rac);
256 prefetchw(&page->flags);
259 if (page_has_buffers(page))
262 block_in_file = next_block =
263 (sector_t)page->index << (PAGE_SHIFT - blkbits);
264 last_block = block_in_file + nr_pages * blocks_per_page;
265 last_block_in_file = (ext4_readpage_limit(inode) +
266 blocksize - 1) >> blkbits;
267 if (last_block > last_block_in_file)
268 last_block = last_block_in_file;
272 * Map blocks using the previous result first.
274 if ((map.m_flags & EXT4_MAP_MAPPED) &&
275 block_in_file > map.m_lblk &&
276 block_in_file < (map.m_lblk + map.m_len)) {
277 unsigned map_offset = block_in_file - map.m_lblk;
278 unsigned last = map.m_len - map_offset;
280 for (relative_block = 0; ; relative_block++) {
281 if (relative_block == last) {
283 map.m_flags &= ~EXT4_MAP_MAPPED;
286 if (page_block == blocks_per_page)
288 blocks[page_block] = map.m_pblk + map_offset +
296 * Then do more ext4_map_blocks() calls until we are
297 * done with this page.
299 while (page_block < blocks_per_page) {
300 if (block_in_file < last_block) {
301 map.m_lblk = block_in_file;
302 map.m_len = last_block - block_in_file;
304 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
307 zero_user_segment(page, 0,
313 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
315 if (first_hole == blocks_per_page)
316 first_hole = page_block;
321 if (first_hole != blocks_per_page)
322 goto confused; /* hole -> non-hole */
324 /* Contiguous blocks? */
325 if (page_block && blocks[page_block-1] != map.m_pblk-1)
327 for (relative_block = 0; ; relative_block++) {
328 if (relative_block == map.m_len) {
330 map.m_flags &= ~EXT4_MAP_MAPPED;
332 } else if (page_block == blocks_per_page)
334 blocks[page_block] = map.m_pblk+relative_block;
339 if (first_hole != blocks_per_page) {
340 zero_user_segment(page, first_hole << blkbits,
342 if (first_hole == 0) {
343 if (ext4_need_verity(inode, page->index) &&
344 !fsverity_verify_page(page))
346 SetPageUptodate(page);
350 } else if (fully_mapped) {
351 SetPageMappedToDisk(page);
353 if (fully_mapped && blocks_per_page == 1 &&
354 !PageUptodate(page) && cleancache_get_page(page) == 0) {
355 SetPageUptodate(page);
360 * This page will go to BIO. Do we need to send this
363 if (bio && (last_block_in_bio != blocks[0] - 1 ||
364 !fscrypt_mergeable_bio(bio, inode, next_block))) {
371 * bio_alloc will _always_ be able to allocate a bio if
372 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
374 bio = bio_alloc(GFP_KERNEL,
375 min_t(int, nr_pages, BIO_MAX_PAGES));
376 fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
378 ext4_set_bio_post_read_ctx(bio, inode, page->index);
379 bio_set_dev(bio, bdev);
380 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
381 bio->bi_end_io = mpage_end_io;
382 bio_set_op_attrs(bio, REQ_OP_READ,
383 rac ? REQ_RAHEAD : 0);
386 length = first_hole << blkbits;
387 if (bio_add_page(bio, page, length, 0) < length)
388 goto submit_and_realloc;
390 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
391 (relative_block == map.m_len)) ||
392 (first_hole != blocks_per_page)) {
396 last_block_in_bio = blocks[blocks_per_page - 1];
403 if (!PageUptodate(page))
404 block_read_full_page(page, ext4_get_block);
416 int __init ext4_init_post_read_processing(void)
418 bio_post_read_ctx_cache =
419 kmem_cache_create("ext4_bio_post_read_ctx",
420 sizeof(struct bio_post_read_ctx), 0, 0, NULL);
421 if (!bio_post_read_ctx_cache)
423 bio_post_read_ctx_pool =
424 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
425 bio_post_read_ctx_cache);
426 if (!bio_post_read_ctx_pool)
427 goto fail_free_cache;
431 kmem_cache_destroy(bio_post_read_ctx_cache);
436 void ext4_exit_post_read_processing(void)
438 mempool_destroy(bio_post_read_ctx_pool);
439 kmem_cache_destroy(bio_post_read_ctx_cache);