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Linux/fs/ext4/readpage.c

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  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 #include <linux/cleancache.h>
 47 
 48 #include "ext4.h"
 49 
 50 #define NUM_PREALLOC_POST_READ_CTXS     128
 51 
 52 static struct kmem_cache *bio_post_read_ctx_cache;
 53 static mempool_t *bio_post_read_ctx_pool;
 54 
 55 /* postprocessing steps for read bios */
 56 enum bio_post_read_step {
 57         STEP_INITIAL = 0,
 58         STEP_DECRYPT,
 59         STEP_VERITY,
 60         STEP_MAX,
 61 };
 62 
 63 struct bio_post_read_ctx {
 64         struct bio *bio;
 65         struct work_struct work;
 66         unsigned int cur_step;
 67         unsigned int enabled_steps;
 68 };
 69 
 70 static void __read_end_io(struct bio *bio)
 71 {
 72         struct page *page;
 73         struct bio_vec *bv;
 74         struct bvec_iter_all iter_all;
 75 
 76         bio_for_each_segment_all(bv, bio, iter_all) {
 77                 page = bv->bv_page;
 78 
 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 */
 83                         ClearPageError(page);
 84                 } else {
 85                         SetPageUptodate(page);
 86                 }
 87                 unlock_page(page);
 88         }
 89         if (bio->bi_private)
 90                 mempool_free(bio->bi_private, bio_post_read_ctx_pool);
 91         bio_put(bio);
 92 }
 93 
 94 static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
 95 
 96 static void decrypt_work(struct work_struct *work)
 97 {
 98         struct bio_post_read_ctx *ctx =
 99                 container_of(work, struct bio_post_read_ctx, work);
100 
101         fscrypt_decrypt_bio(ctx->bio);
102 
103         bio_post_read_processing(ctx);
104 }
105 
106 static void verity_work(struct work_struct *work)
107 {
108         struct bio_post_read_ctx *ctx =
109                 container_of(work, struct bio_post_read_ctx, work);
110         struct bio *bio = ctx->bio;
111 
112         /*
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.
118          */
119         BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
120         mempool_free(ctx, bio_post_read_ctx_pool);
121         bio->bi_private = NULL;
122 
123         fsverity_verify_bio(bio);
124 
125         __read_end_io(bio);
126 }
127 
128 static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
129 {
130         /*
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.
134          */
135         switch (++ctx->cur_step) {
136         case STEP_DECRYPT:
137                 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
138                         INIT_WORK(&ctx->work, decrypt_work);
139                         fscrypt_enqueue_decrypt_work(&ctx->work);
140                         return;
141                 }
142                 ctx->cur_step++;
143                 fallthrough;
144         case STEP_VERITY:
145                 if (ctx->enabled_steps & (1 << STEP_VERITY)) {
146                         INIT_WORK(&ctx->work, verity_work);
147                         fsverity_enqueue_verify_work(&ctx->work);
148                         return;
149                 }
150                 ctx->cur_step++;
151                 fallthrough;
152         default:
153                 __read_end_io(ctx->bio);
154         }
155 }
156 
157 static bool bio_post_read_required(struct bio *bio)
158 {
159         return bio->bi_private && !bio->bi_status;
160 }
161 
162 /*
163  * I/O completion handler for multipage BIOs.
164  *
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().
168  *
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.
173  */
174 static void mpage_end_io(struct bio *bio)
175 {
176         if (bio_post_read_required(bio)) {
177                 struct bio_post_read_ctx *ctx = bio->bi_private;
178 
179                 ctx->cur_step = STEP_INITIAL;
180                 bio_post_read_processing(ctx);
181                 return;
182         }
183         __read_end_io(bio);
184 }
185 
186 static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
187 {
188         return fsverity_active(inode) &&
189                idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
190 }
191 
192 static void ext4_set_bio_post_read_ctx(struct bio *bio,
193                                        const struct inode *inode,
194                                        pgoff_t first_idx)
195 {
196         unsigned int post_read_steps = 0;
197 
198         if (fscrypt_inode_uses_fs_layer_crypto(inode))
199                 post_read_steps |= 1 << STEP_DECRYPT;
200 
201         if (ext4_need_verity(inode, first_idx))
202                 post_read_steps |= 1 << STEP_VERITY;
203 
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);
208 
209                 ctx->bio = bio;
210                 ctx->enabled_steps = post_read_steps;
211                 bio->bi_private = ctx;
212         }
213 }
214 
215 static inline loff_t ext4_readpage_limit(struct inode *inode)
216 {
217         if (IS_ENABLED(CONFIG_FS_VERITY) &&
218             (IS_VERITY(inode) || ext4_verity_in_progress(inode)))
219                 return inode->i_sb->s_maxbytes;
220 
221         return i_size_read(inode);
222 }
223 
224 int ext4_mpage_readpages(struct inode *inode,
225                 struct readahead_control *rac, struct page *page)
226 {
227         struct bio *bio = NULL;
228         sector_t last_block_in_bio = 0;
229 
230         const unsigned blkbits = inode->i_blkbits;
231         const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
232         const unsigned blocksize = 1 << blkbits;
233         sector_t next_block;
234         sector_t block_in_file;
235         sector_t last_block;
236         sector_t last_block_in_file;
237         sector_t blocks[MAX_BUF_PER_PAGE];
238         unsigned page_block;
239         struct block_device *bdev = inode->i_sb->s_bdev;
240         int length;
241         unsigned relative_block = 0;
242         struct ext4_map_blocks map;
243         unsigned int nr_pages = rac ? readahead_count(rac) : 1;
244 
245         map.m_pblk = 0;
246         map.m_lblk = 0;
247         map.m_len = 0;
248         map.m_flags = 0;
249 
250         for (; nr_pages; nr_pages--) {
251                 int fully_mapped = 1;
252                 unsigned first_hole = blocks_per_page;
253 
254                 if (rac) {
255                         page = readahead_page(rac);
256                         prefetchw(&page->flags);
257                 }
258 
259                 if (page_has_buffers(page))
260                         goto confused;
261 
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;
269                 page_block = 0;
270 
271                 /*
272                  * Map blocks using the previous result first.
273                  */
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;
279 
280                         for (relative_block = 0; ; relative_block++) {
281                                 if (relative_block == last) {
282                                         /* needed? */
283                                         map.m_flags &= ~EXT4_MAP_MAPPED;
284                                         break;
285                                 }
286                                 if (page_block == blocks_per_page)
287                                         break;
288                                 blocks[page_block] = map.m_pblk + map_offset +
289                                         relative_block;
290                                 page_block++;
291                                 block_in_file++;
292                         }
293                 }
294 
295                 /*
296                  * Then do more ext4_map_blocks() calls until we are
297                  * done with this page.
298                  */
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;
303 
304                                 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
305                                 set_error_page:
306                                         SetPageError(page);
307                                         zero_user_segment(page, 0,
308                                                           PAGE_SIZE);
309                                         unlock_page(page);
310                                         goto next_page;
311                                 }
312                         }
313                         if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
314                                 fully_mapped = 0;
315                                 if (first_hole == blocks_per_page)
316                                         first_hole = page_block;
317                                 page_block++;
318                                 block_in_file++;
319                                 continue;
320                         }
321                         if (first_hole != blocks_per_page)
322                                 goto confused;          /* hole -> non-hole */
323 
324                         /* Contiguous blocks? */
325                         if (page_block && blocks[page_block-1] != map.m_pblk-1)
326                                 goto confused;
327                         for (relative_block = 0; ; relative_block++) {
328                                 if (relative_block == map.m_len) {
329                                         /* needed? */
330                                         map.m_flags &= ~EXT4_MAP_MAPPED;
331                                         break;
332                                 } else if (page_block == blocks_per_page)
333                                         break;
334                                 blocks[page_block] = map.m_pblk+relative_block;
335                                 page_block++;
336                                 block_in_file++;
337                         }
338                 }
339                 if (first_hole != blocks_per_page) {
340                         zero_user_segment(page, first_hole << blkbits,
341                                           PAGE_SIZE);
342                         if (first_hole == 0) {
343                                 if (ext4_need_verity(inode, page->index) &&
344                                     !fsverity_verify_page(page))
345                                         goto set_error_page;
346                                 SetPageUptodate(page);
347                                 unlock_page(page);
348                                 goto next_page;
349                         }
350                 } else if (fully_mapped) {
351                         SetPageMappedToDisk(page);
352                 }
353                 if (fully_mapped && blocks_per_page == 1 &&
354                     !PageUptodate(page) && cleancache_get_page(page) == 0) {
355                         SetPageUptodate(page);
356                         goto confused;
357                 }
358 
359                 /*
360                  * This page will go to BIO.  Do we need to send this
361                  * BIO off first?
362                  */
363                 if (bio && (last_block_in_bio != blocks[0] - 1 ||
364                             !fscrypt_mergeable_bio(bio, inode, next_block))) {
365                 submit_and_realloc:
366                         submit_bio(bio);
367                         bio = NULL;
368                 }
369                 if (bio == NULL) {
370                         /*
371                          * bio_alloc will _always_ be able to allocate a bio if
372                          * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
373                          */
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,
377                                                   GFP_KERNEL);
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);
384                 }
385 
386                 length = first_hole << blkbits;
387                 if (bio_add_page(bio, page, length, 0) < length)
388                         goto submit_and_realloc;
389 
390                 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
391                      (relative_block == map.m_len)) ||
392                     (first_hole != blocks_per_page)) {
393                         submit_bio(bio);
394                         bio = NULL;
395                 } else
396                         last_block_in_bio = blocks[blocks_per_page - 1];
397                 goto next_page;
398         confused:
399                 if (bio) {
400                         submit_bio(bio);
401                         bio = NULL;
402                 }
403                 if (!PageUptodate(page))
404                         block_read_full_page(page, ext4_get_block);
405                 else
406                         unlock_page(page);
407         next_page:
408                 if (rac)
409                         put_page(page);
410         }
411         if (bio)
412                 submit_bio(bio);
413         return 0;
414 }
415 
416 int __init ext4_init_post_read_processing(void)
417 {
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)
422                 goto fail;
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;
428         return 0;
429 
430 fail_free_cache:
431         kmem_cache_destroy(bio_post_read_ctx_cache);
432 fail:
433         return -ENOMEM;
434 }
435 
436 void ext4_exit_post_read_processing(void)
437 {
438         mempool_destroy(bio_post_read_ctx_pool);
439         kmem_cache_destroy(bio_post_read_ctx_cache);
440 }
441 

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