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 intent is the ext4_mpage_readpages() function here is intended
11 * to replace mpage_readpages() 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 struct bio_post_read_ctx *get_bio_post_read_ctx(struct inode *inode,
196 unsigned int post_read_steps = 0;
197 struct bio_post_read_ctx *ctx = NULL;
199 if (IS_ENCRYPTED(inode) && S_ISREG(inode->i_mode))
200 post_read_steps |= 1 << STEP_DECRYPT;
202 if (ext4_need_verity(inode, first_idx))
203 post_read_steps |= 1 << STEP_VERITY;
205 if (post_read_steps) {
206 ctx = mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
208 return ERR_PTR(-ENOMEM);
210 ctx->enabled_steps = post_read_steps;
211 bio->bi_private = ctx;
216 static inline loff_t ext4_readpage_limit(struct inode *inode)
218 if (IS_ENABLED(CONFIG_FS_VERITY) &&
219 (IS_VERITY(inode) || ext4_verity_in_progress(inode)))
220 return inode->i_sb->s_maxbytes;
222 return i_size_read(inode);
225 int ext4_mpage_readpages(struct address_space *mapping,
226 struct list_head *pages, struct page *page,
227 unsigned nr_pages, bool is_readahead)
229 struct bio *bio = NULL;
230 sector_t last_block_in_bio = 0;
232 struct inode *inode = mapping->host;
233 const unsigned blkbits = inode->i_blkbits;
234 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
235 const unsigned blocksize = 1 << blkbits;
236 sector_t block_in_file;
238 sector_t last_block_in_file;
239 sector_t blocks[MAX_BUF_PER_PAGE];
241 struct block_device *bdev = inode->i_sb->s_bdev;
243 unsigned relative_block = 0;
244 struct ext4_map_blocks map;
251 for (; nr_pages; nr_pages--) {
252 int fully_mapped = 1;
253 unsigned first_hole = blocks_per_page;
256 page = lru_to_page(pages);
258 prefetchw(&page->flags);
259 list_del(&page->lru);
260 if (add_to_page_cache_lru(page, mapping, page->index,
261 readahead_gfp_mask(mapping)))
265 if (page_has_buffers(page))
268 block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
269 last_block = block_in_file + nr_pages * blocks_per_page;
270 last_block_in_file = (ext4_readpage_limit(inode) +
271 blocksize - 1) >> blkbits;
272 if (last_block > last_block_in_file)
273 last_block = last_block_in_file;
277 * Map blocks using the previous result first.
279 if ((map.m_flags & EXT4_MAP_MAPPED) &&
280 block_in_file > map.m_lblk &&
281 block_in_file < (map.m_lblk + map.m_len)) {
282 unsigned map_offset = block_in_file - map.m_lblk;
283 unsigned last = map.m_len - map_offset;
285 for (relative_block = 0; ; relative_block++) {
286 if (relative_block == last) {
288 map.m_flags &= ~EXT4_MAP_MAPPED;
291 if (page_block == blocks_per_page)
293 blocks[page_block] = map.m_pblk + map_offset +
301 * Then do more ext4_map_blocks() calls until we are
302 * done with this page.
304 while (page_block < blocks_per_page) {
305 if (block_in_file < last_block) {
306 map.m_lblk = block_in_file;
307 map.m_len = last_block - block_in_file;
309 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
312 zero_user_segment(page, 0,
318 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
320 if (first_hole == blocks_per_page)
321 first_hole = page_block;
326 if (first_hole != blocks_per_page)
327 goto confused; /* hole -> non-hole */
329 /* Contiguous blocks? */
330 if (page_block && blocks[page_block-1] != map.m_pblk-1)
332 for (relative_block = 0; ; relative_block++) {
333 if (relative_block == map.m_len) {
335 map.m_flags &= ~EXT4_MAP_MAPPED;
337 } else if (page_block == blocks_per_page)
339 blocks[page_block] = map.m_pblk+relative_block;
344 if (first_hole != blocks_per_page) {
345 zero_user_segment(page, first_hole << blkbits,
347 if (first_hole == 0) {
348 if (ext4_need_verity(inode, page->index) &&
349 !fsverity_verify_page(page))
351 SetPageUptodate(page);
355 } else if (fully_mapped) {
356 SetPageMappedToDisk(page);
358 if (fully_mapped && blocks_per_page == 1 &&
359 !PageUptodate(page) && cleancache_get_page(page) == 0) {
360 SetPageUptodate(page);
365 * This page will go to BIO. Do we need to send this
368 if (bio && (last_block_in_bio != blocks[0] - 1)) {
374 struct bio_post_read_ctx *ctx;
376 bio = bio_alloc(GFP_KERNEL,
377 min_t(int, nr_pages, BIO_MAX_PAGES));
380 ctx = get_bio_post_read_ctx(inode, bio, page->index);
386 bio_set_dev(bio, bdev);
387 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
388 bio->bi_end_io = mpage_end_io;
389 bio->bi_private = ctx;
390 bio_set_op_attrs(bio, REQ_OP_READ,
391 is_readahead ? REQ_RAHEAD : 0);
394 length = first_hole << blkbits;
395 if (bio_add_page(bio, page, length, 0) < length)
396 goto submit_and_realloc;
398 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
399 (relative_block == map.m_len)) ||
400 (first_hole != blocks_per_page)) {
404 last_block_in_bio = blocks[blocks_per_page - 1];
411 if (!PageUptodate(page))
412 block_read_full_page(page, ext4_get_block);
419 BUG_ON(pages && !list_empty(pages));
425 int __init ext4_init_post_read_processing(void)
427 bio_post_read_ctx_cache =
428 kmem_cache_create("ext4_bio_post_read_ctx",
429 sizeof(struct bio_post_read_ctx), 0, 0, NULL);
430 if (!bio_post_read_ctx_cache)
432 bio_post_read_ctx_pool =
433 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
434 bio_post_read_ctx_cache);
435 if (!bio_post_read_ctx_pool)
436 goto fail_free_cache;
440 kmem_cache_destroy(bio_post_read_ctx_cache);
445 void ext4_exit_post_read_processing(void)
447 mempool_destroy(bio_post_read_ctx_pool);
448 kmem_cache_destroy(bio_post_read_ctx_cache);