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 51 static struct kmem_cache *bio_post_read_ctx_cache; 52 static mempool_t *bio_post_read_ctx_pool; 53 54 /* postprocessing steps for read bios */ 55 enum bio_post_read_step { 56 STEP_INITIAL = 0, 57 STEP_DECRYPT, 58 STEP_VERITY, 59 STEP_MAX, 60 }; 61 62 struct 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 69 static 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 80 static void bio_post_read_processing(struct bio_post_read_ctx *ctx); 81 82 static 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 94 static 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(ctx, bio_post_read_ctx_pool); 109 bio->bi_private = NULL; 110 111 fsverity_verify_bio(bio); 112 113 __read_end_io(bio); 114 } 115 116 static 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(&ctx->work); 136 return; 137 } 138 ctx->cur_step++; 139 fallthrough; 140 default: 141 __read_end_io(ctx->bio); 142 } 143 } 144 145 static 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 */ 162 static 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 } 173 174 static 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 } 179 180 static 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 } 202 203 static 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 } 210 211 int 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 const unsigned blkbits = inode->i_blkbits; 217 const unsigned blocksize = 1 << blkbits; 218 sector_t next_block; 219 sector_t block_in_file; 220 sector_t last_block; 221 sector_t last_block_in_file; 222 sector_t first_block; 223 unsigned page_block; 224 struct block_device *bdev = inode->i_sb->s_bdev; 225 int length; 226 unsigned relative_block = 0; 227 struct ext4_map_blocks map; 228 unsigned int nr_pages, folio_pages; 229 230 map.m_pblk = 0; 231 map.m_lblk = 0; 232 map.m_len = 0; 233 map.m_flags = 0; 234 235 nr_pages = rac ? readahead_count(rac) : folio_nr_pages(folio); 236 for (; nr_pages; nr_pages -= folio_pages) { 237 int fully_mapped = 1; 238 unsigned int first_hole; 239 unsigned int blocks_per_folio; 240 241 if (rac) 242 folio = readahead_folio(rac); 243 244 folio_pages = folio_nr_pages(folio); 245 prefetchw(&folio->flags); 246 247 if (folio_buffers(folio)) 248 goto confused; 249 250 blocks_per_folio = folio_size(folio) >> blkbits; 251 first_hole = blocks_per_folio; 252 block_in_file = next_block = EXT4_PG_TO_LBLK(inode, folio->index); 253 last_block = EXT4_PG_TO_LBLK(inode, folio->index + nr_pages); 254 last_block_in_file = (ext4_readpage_limit(inode) + 255 blocksize - 1) >> blkbits; 256 if (last_block > last_block_in_file) 257 last_block = last_block_in_file; 258 page_block = 0; 259 260 /* 261 * Map blocks using the previous result first. 262 */ 263 if ((map.m_flags & EXT4_MAP_MAPPED) && 264 block_in_file > map.m_lblk && 265 block_in_file < (map.m_lblk + map.m_len)) { 266 unsigned map_offset = block_in_file - map.m_lblk; 267 unsigned last = map.m_len - map_offset; 268 269 first_block = map.m_pblk + map_offset; 270 for (relative_block = 0; ; relative_block++) { 271 if (relative_block == last) { 272 /* needed? */ 273 map.m_flags &= ~EXT4_MAP_MAPPED; 274 break; 275 } 276 if (page_block == blocks_per_folio) 277 break; 278 page_block++; 279 block_in_file++; 280 } 281 } 282 283 /* 284 * Then do more ext4_map_blocks() calls until we are 285 * done with this folio. 286 */ 287 while (page_block < blocks_per_folio) { 288 if (block_in_file < last_block) { 289 map.m_lblk = block_in_file; 290 map.m_len = last_block - block_in_file; 291 292 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) { 293 set_error_page: 294 folio_zero_segment(folio, 0, 295 folio_size(folio)); 296 folio_unlock(folio); 297 goto next_page; 298 } 299 } 300 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) { 301 fully_mapped = 0; 302 if (first_hole == blocks_per_folio) 303 first_hole = page_block; 304 page_block++; 305 block_in_file++; 306 continue; 307 } 308 if (first_hole != blocks_per_folio) 309 goto confused; /* hole -> non-hole */ 310 311 /* Contiguous blocks? */ 312 if (!page_block) 313 first_block = map.m_pblk; 314 else if (first_block + page_block != map.m_pblk) 315 goto confused; 316 for (relative_block = 0; ; relative_block++) { 317 if (relative_block == map.m_len) { 318 /* needed? */ 319 map.m_flags &= ~EXT4_MAP_MAPPED; 320 break; 321 } else if (page_block == blocks_per_folio) 322 break; 323 page_block++; 324 block_in_file++; 325 } 326 } 327 if (first_hole != blocks_per_folio) { 328 folio_zero_segment(folio, first_hole << blkbits, 329 folio_size(folio)); 330 if (first_hole == 0) { 331 if (ext4_need_verity(inode, folio->index) && 332 !fsverity_verify_folio(folio)) 333 goto set_error_page; 334 folio_end_read(folio, true); 335 continue; 336 } 337 } else if (fully_mapped) { 338 folio_set_mappedtodisk(folio); 339 } 340 341 /* 342 * This folio will go to BIO. Do we need to send this 343 * BIO off first? 344 */ 345 if (bio && (last_block_in_bio != first_block - 1 || 346 !fscrypt_mergeable_bio(bio, inode, next_block))) { 347 submit_and_realloc: 348 submit_bio(bio); 349 bio = NULL; 350 } 351 if (bio == NULL) { 352 /* 353 * bio_alloc will _always_ be able to allocate a bio if 354 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset(). 355 */ 356 bio = bio_alloc(bdev, bio_max_segs(nr_pages), 357 REQ_OP_READ, GFP_KERNEL); 358 fscrypt_set_bio_crypt_ctx(bio, inode, next_block, 359 GFP_KERNEL); 360 ext4_set_bio_post_read_ctx(bio, inode, folio->index); 361 bio->bi_iter.bi_sector = first_block << (blkbits - 9); 362 bio->bi_end_io = mpage_end_io; 363 if (rac) 364 bio->bi_opf |= REQ_RAHEAD; 365 } 366 367 length = first_hole << blkbits; 368 if (!bio_add_folio(bio, folio, length, 0)) 369 goto submit_and_realloc; 370 371 if (((map.m_flags & EXT4_MAP_BOUNDARY) && 372 (relative_block == map.m_len)) || 373 (first_hole != blocks_per_folio)) { 374 submit_bio(bio); 375 bio = NULL; 376 } else 377 last_block_in_bio = first_block + blocks_per_folio - 1; 378 continue; 379 confused: 380 if (bio) { 381 submit_bio(bio); 382 bio = NULL; 383 } 384 if (!folio_test_uptodate(folio)) 385 block_read_full_folio(folio, ext4_get_block); 386 else 387 folio_unlock(folio); 388 next_page: 389 ; /* A label shall be followed by a statement until C23 */ 390 } 391 if (bio) 392 submit_bio(bio); 393 return 0; 394 } 395 396 int __init ext4_init_post_read_processing(void) 397 { 398 bio_post_read_ctx_cache = KMEM_CACHE(bio_post_read_ctx, SLAB_RECLAIM_ACCOUNT); 399 400 if (!bio_post_read_ctx_cache) 401 goto fail; 402 bio_post_read_ctx_pool = 403 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS, 404 bio_post_read_ctx_cache); 405 if (!bio_post_read_ctx_pool) 406 goto fail_free_cache; 407 return 0; 408 409 fail_free_cache: 410 kmem_cache_destroy(bio_post_read_ctx_cache); 411 fail: 412 return -ENOMEM; 413 } 414 415 void ext4_exit_post_read_processing(void) 416 { 417 mempool_destroy(bio_post_read_ctx_pool); 418 kmem_cache_destroy(bio_post_read_ctx_cache); 419 } 420