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1// SPDX-License-Identifier: GPL-2.02/*3 * linux/fs/ext4/readpage.c4 *5 * Copyright (C) 2002, Linus Torvalds.6 * Copyright (C) 2015, Google, Inc.7 *8 * This was originally taken from fs/mpage.c9 *10 * The ext4_mpage_readpages() function here is intended to11 * replace mpage_readahead() in the general case, not just for12 * encrypted files. It has some limitations (see below), where it13 * will fall back to read_block_full_page(), but these limitations14 * should only be hit when page_size != block_size.15 *16 * This will allow us to attach a callback function to support ext417 * encryption.18 *19 * If anything unusual happens, such as:20 *21 * - encountering a page which has buffers22 * - encountering a page which has a non-hole after a hole23 * - encountering a page with non-contiguous blocks24 *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 12850 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(fi.folio, bio->bi_status == 0);75 if (bio->bi_private)76 mempool_free(bio->bi_private, 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 else91 __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 verity102 * will be disabled for that, decryption may still be needed, causing103 * another bio_post_read_ctx to be allocated. So to guarantee that104 * 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(ctx, 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 because120 * verity may require reading metadata pages that need decryption, and121 * 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(&ctx->work);136 return;137 }138 ctx->cur_step++;139 fallthrough;140 default:141 __read_end_io(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 falls155 * back to block_read_full_folio().156 *157 * Why is this? If a page's completion depends on a number of different BIOs158 * which can complete in any order (or at the same time) then determining the159 * 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, 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 = rac ? readahead_count(rac) : 1;231 232 map.m_pblk = 0;233 map.m_lblk = 0;234 map.m_len = 0;235 map.m_flags = 0;236 237 for (; nr_pages; nr_pages--) {238 int fully_mapped = 1;239 unsigned first_hole = blocks_per_page;240 241 if (rac)242 folio = readahead_folio(rac);243 prefetchw(&folio->flags);244 245 if (folio_buffers(folio))246 goto confused;247 248 block_in_file = next_block =249 (sector_t)folio->index << (PAGE_SHIFT - blkbits);250 last_block = block_in_file + nr_pages * blocks_per_page;251 last_block_in_file = (ext4_readpage_limit(inode) +252 blocksize - 1) >> blkbits;253 if (last_block > last_block_in_file)254 last_block = last_block_in_file;255 page_block = 0;256 257 /*258 * Map blocks using the previous result first.259 */260 if ((map.m_flags & EXT4_MAP_MAPPED) &&261 block_in_file > map.m_lblk &&262 block_in_file < (map.m_lblk + map.m_len)) {263 unsigned map_offset = block_in_file - map.m_lblk;264 unsigned last = map.m_len - map_offset;265 266 first_block = map.m_pblk + map_offset;267 for (relative_block = 0; ; relative_block++) {268 if (relative_block == last) {269 /* needed? */270 map.m_flags &= ~EXT4_MAP_MAPPED;271 break;272 }273 if (page_block == blocks_per_page)274 break;275 page_block++;276 block_in_file++;277 }278 }279 280 /*281 * Then do more ext4_map_blocks() calls until we are282 * done with this folio.283 */284 while (page_block < blocks_per_page) {285 if (block_in_file < last_block) {286 map.m_lblk = block_in_file;287 map.m_len = last_block - block_in_file;288 289 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {290 set_error_page:291 folio_zero_segment(folio, 0,292 folio_size(folio));293 folio_unlock(folio);294 goto next_page;295 }296 }297 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {298 fully_mapped = 0;299 if (first_hole == blocks_per_page)300 first_hole = page_block;301 page_block++;302 block_in_file++;303 continue;304 }305 if (first_hole != blocks_per_page)306 goto confused; /* hole -> non-hole */307 308 /* Contiguous blocks? */309 if (!page_block)310 first_block = map.m_pblk;311 else if (first_block + page_block != map.m_pblk)312 goto confused;313 for (relative_block = 0; ; relative_block++) {314 if (relative_block == map.m_len) {315 /* needed? */316 map.m_flags &= ~EXT4_MAP_MAPPED;317 break;318 } else if (page_block == blocks_per_page)319 break;320 page_block++;321 block_in_file++;322 }323 }324 if (first_hole != blocks_per_page) {325 folio_zero_segment(folio, first_hole << blkbits,326 folio_size(folio));327 if (first_hole == 0) {328 if (ext4_need_verity(inode, folio->index) &&329 !fsverity_verify_folio(folio))330 goto set_error_page;331 folio_end_read(folio, true);332 continue;333 }334 } else if (fully_mapped) {335 folio_set_mappedtodisk(folio);336 }337 338 /*339 * This folio will go to BIO. Do we need to send this340 * BIO off first?341 */342 if (bio && (last_block_in_bio != first_block - 1 ||343 !fscrypt_mergeable_bio(bio, inode, next_block))) {344 submit_and_realloc:345 submit_bio(bio);346 bio = NULL;347 }348 if (bio == NULL) {349 /*350 * bio_alloc will _always_ be able to allocate a bio if351 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().352 */353 bio = bio_alloc(bdev, bio_max_segs(nr_pages),354 REQ_OP_READ, GFP_KERNEL);355 fscrypt_set_bio_crypt_ctx(bio, inode, next_block,356 GFP_KERNEL);357 ext4_set_bio_post_read_ctx(bio, inode, folio->index);358 bio->bi_iter.bi_sector = first_block << (blkbits - 9);359 bio->bi_end_io = mpage_end_io;360 if (rac)361 bio->bi_opf |= REQ_RAHEAD;362 }363 364 length = first_hole << blkbits;365 if (!bio_add_folio(bio, folio, length, 0))366 goto submit_and_realloc;367 368 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&369 (relative_block == map.m_len)) ||370 (first_hole != blocks_per_page)) {371 submit_bio(bio);372 bio = NULL;373 } else374 last_block_in_bio = first_block + blocks_per_page - 1;375 continue;376 confused:377 if (bio) {378 submit_bio(bio);379 bio = NULL;380 }381 if (!folio_test_uptodate(folio))382 block_read_full_folio(folio, ext4_get_block);383 else384 folio_unlock(folio);385next_page:386 ; /* A label shall be followed by a statement until C23 */387 }388 if (bio)389 submit_bio(bio);390 return 0;391}392 393int __init ext4_init_post_read_processing(void)394{395 bio_post_read_ctx_cache = KMEM_CACHE(bio_post_read_ctx, SLAB_RECLAIM_ACCOUNT);396 397 if (!bio_post_read_ctx_cache)398 goto fail;399 bio_post_read_ctx_pool =400 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,401 bio_post_read_ctx_cache);402 if (!bio_post_read_ctx_pool)403 goto fail_free_cache;404 return 0;405 406fail_free_cache:407 kmem_cache_destroy(bio_post_read_ctx_cache);408fail:409 return -ENOMEM;410}411 412void ext4_exit_post_read_processing(void)413{414 mempool_destroy(bio_post_read_ctx_pool);415 kmem_cache_destroy(bio_post_read_ctx_cache);416}417