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>
49 #define NUM_PREALLOC_POST_READ_CTXS 128
51 static struct kmem_cache *bio_post_read_ctx_cache;
52 static mempool_t *bio_post_read_ctx_pool;
54 /* postprocessing steps for read bios */
55 enum bio_post_read_step {
62 struct bio_post_read_ctx {
64 struct work_struct work;
65 unsigned int cur_step;
66 unsigned int enabled_steps;
69 static void __read_end_io(struct bio *bio)
73 struct bvec_iter_all iter_all;
75 bio_for_each_segment_all(bv, bio, iter_all) {
79 ClearPageUptodate(page);
81 SetPageUptodate(page);
85 mempool_free(bio->bi_private, bio_post_read_ctx_pool);
89 static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
91 static void decrypt_work(struct work_struct *work)
93 struct bio_post_read_ctx *ctx =
94 container_of(work, struct bio_post_read_ctx, work);
95 struct bio *bio = ctx->bio;
97 if (fscrypt_decrypt_bio(bio))
98 bio_post_read_processing(ctx);
103 static void verity_work(struct work_struct *work)
105 struct bio_post_read_ctx *ctx =
106 container_of(work, struct bio_post_read_ctx, work);
107 struct bio *bio = ctx->bio;
110 * fsverity_verify_bio() may call readahead() again, and although verity
111 * will be disabled for that, decryption may still be needed, causing
112 * another bio_post_read_ctx to be allocated. So to guarantee that
113 * mempool_alloc() never deadlocks we must free the current ctx first.
114 * This is safe because verity is the last post-read step.
116 BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
117 mempool_free(ctx, bio_post_read_ctx_pool);
118 bio->bi_private = NULL;
120 fsverity_verify_bio(bio);
125 static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
128 * We use different work queues for decryption and for verity because
129 * verity may require reading metadata pages that need decryption, and
130 * we shouldn't recurse to the same workqueue.
132 switch (++ctx->cur_step) {
134 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
135 INIT_WORK(&ctx->work, decrypt_work);
136 fscrypt_enqueue_decrypt_work(&ctx->work);
142 if (ctx->enabled_steps & (1 << STEP_VERITY)) {
143 INIT_WORK(&ctx->work, verity_work);
144 fsverity_enqueue_verify_work(&ctx->work);
150 __read_end_io(ctx->bio);
154 static bool bio_post_read_required(struct bio *bio)
156 return bio->bi_private && !bio->bi_status;
160 * I/O completion handler for multipage BIOs.
162 * The mpage code never puts partial pages into a BIO (except for end-of-file).
163 * If a page does not map to a contiguous run of blocks then it simply falls
164 * back to block_read_full_folio().
166 * Why is this? If a page's completion depends on a number of different BIOs
167 * which can complete in any order (or at the same time) then determining the
168 * status of that page is hard. See end_buffer_async_read() for the details.
169 * There is no point in duplicating all that complexity.
171 static void mpage_end_io(struct bio *bio)
173 if (bio_post_read_required(bio)) {
174 struct bio_post_read_ctx *ctx = bio->bi_private;
176 ctx->cur_step = STEP_INITIAL;
177 bio_post_read_processing(ctx);
183 static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
185 return fsverity_active(inode) &&
186 idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
189 static void ext4_set_bio_post_read_ctx(struct bio *bio,
190 const struct inode *inode,
193 unsigned int post_read_steps = 0;
195 if (fscrypt_inode_uses_fs_layer_crypto(inode))
196 post_read_steps |= 1 << STEP_DECRYPT;
198 if (ext4_need_verity(inode, first_idx))
199 post_read_steps |= 1 << STEP_VERITY;
201 if (post_read_steps) {
202 /* Due to the mempool, this never fails. */
203 struct bio_post_read_ctx *ctx =
204 mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
207 ctx->enabled_steps = post_read_steps;
208 bio->bi_private = ctx;
212 static inline loff_t ext4_readpage_limit(struct inode *inode)
214 if (IS_ENABLED(CONFIG_FS_VERITY) && IS_VERITY(inode))
215 return inode->i_sb->s_maxbytes;
217 return i_size_read(inode);
220 int ext4_mpage_readpages(struct inode *inode,
221 struct readahead_control *rac, struct page *page)
223 struct bio *bio = NULL;
224 sector_t last_block_in_bio = 0;
226 const unsigned blkbits = inode->i_blkbits;
227 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
228 const unsigned blocksize = 1 << blkbits;
230 sector_t block_in_file;
232 sector_t last_block_in_file;
233 sector_t blocks[MAX_BUF_PER_PAGE];
235 struct block_device *bdev = inode->i_sb->s_bdev;
237 unsigned relative_block = 0;
238 struct ext4_map_blocks map;
239 unsigned int nr_pages = rac ? readahead_count(rac) : 1;
246 for (; nr_pages; nr_pages--) {
247 int fully_mapped = 1;
248 unsigned first_hole = blocks_per_page;
251 page = readahead_page(rac);
252 prefetchw(&page->flags);
255 if (page_has_buffers(page))
258 block_in_file = next_block =
259 (sector_t)page->index << (PAGE_SHIFT - blkbits);
260 last_block = block_in_file + nr_pages * blocks_per_page;
261 last_block_in_file = (ext4_readpage_limit(inode) +
262 blocksize - 1) >> blkbits;
263 if (last_block > last_block_in_file)
264 last_block = last_block_in_file;
268 * Map blocks using the previous result first.
270 if ((map.m_flags & EXT4_MAP_MAPPED) &&
271 block_in_file > map.m_lblk &&
272 block_in_file < (map.m_lblk + map.m_len)) {
273 unsigned map_offset = block_in_file - map.m_lblk;
274 unsigned last = map.m_len - map_offset;
276 for (relative_block = 0; ; relative_block++) {
277 if (relative_block == last) {
279 map.m_flags &= ~EXT4_MAP_MAPPED;
282 if (page_block == blocks_per_page)
284 blocks[page_block] = map.m_pblk + map_offset +
292 * Then do more ext4_map_blocks() calls until we are
293 * done with this page.
295 while (page_block < blocks_per_page) {
296 if (block_in_file < last_block) {
297 map.m_lblk = block_in_file;
298 map.m_len = last_block - block_in_file;
300 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
303 zero_user_segment(page, 0,
309 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
311 if (first_hole == blocks_per_page)
312 first_hole = page_block;
317 if (first_hole != blocks_per_page)
318 goto confused; /* hole -> non-hole */
320 /* Contiguous blocks? */
321 if (page_block && blocks[page_block-1] != map.m_pblk-1)
323 for (relative_block = 0; ; relative_block++) {
324 if (relative_block == map.m_len) {
326 map.m_flags &= ~EXT4_MAP_MAPPED;
328 } else if (page_block == blocks_per_page)
330 blocks[page_block] = map.m_pblk+relative_block;
335 if (first_hole != blocks_per_page) {
336 zero_user_segment(page, first_hole << blkbits,
338 if (first_hole == 0) {
339 if (ext4_need_verity(inode, page->index) &&
340 !fsverity_verify_page(page))
342 SetPageUptodate(page);
346 } else if (fully_mapped) {
347 SetPageMappedToDisk(page);
351 * This page will go to BIO. Do we need to send this
354 if (bio && (last_block_in_bio != blocks[0] - 1 ||
355 !fscrypt_mergeable_bio(bio, inode, next_block))) {
362 * bio_alloc will _always_ be able to allocate a bio if
363 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
365 bio = bio_alloc(bdev, bio_max_segs(nr_pages),
366 REQ_OP_READ, GFP_KERNEL);
367 fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
369 ext4_set_bio_post_read_ctx(bio, inode, page->index);
370 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
371 bio->bi_end_io = mpage_end_io;
373 bio->bi_opf |= REQ_RAHEAD;
376 length = first_hole << blkbits;
377 if (bio_add_page(bio, page, length, 0) < length)
378 goto submit_and_realloc;
380 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
381 (relative_block == map.m_len)) ||
382 (first_hole != blocks_per_page)) {
386 last_block_in_bio = blocks[blocks_per_page - 1];
393 if (!PageUptodate(page))
394 block_read_full_folio(page_folio(page), ext4_get_block);
406 int __init ext4_init_post_read_processing(void)
408 bio_post_read_ctx_cache = KMEM_CACHE(bio_post_read_ctx, SLAB_RECLAIM_ACCOUNT);
410 if (!bio_post_read_ctx_cache)
412 bio_post_read_ctx_pool =
413 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
414 bio_post_read_ctx_cache);
415 if (!bio_post_read_ctx_pool)
416 goto fail_free_cache;
420 kmem_cache_destroy(bio_post_read_ctx_cache);
425 void ext4_exit_post_read_processing(void)
427 mempool_destroy(bio_post_read_ctx_pool);
428 kmem_cache_destroy(bio_post_read_ctx_cache);