root/drivers/md/dm-verity-fec.c

DEFINITIONS

1. verity_fec_is_enabled
2. fec_interleave
3. fec_decode_rs8
4. fec_read_parity
5. fec_buffer_rs_block
6. fec_buffer_rs_index
7. fec_decode_bufs
8. fec_is_erasure
9. fec_read_bufs
10. fec_alloc_bufs
11. fec_init_bufs
12. fec_decode_rsb
13. fec_bv_copy
14. verity_fec_decode
15. verity_fec_finish_io
16. verity_fec_init_io
17. verity_fec_status_table
18. verity_fec_dtr
19. fec_rs_alloc
20. fec_rs_free
21. verity_is_fec_opt_arg
22. verity_fec_parse_opt_args
23. verity_fec_ctr_alloc
24. verity_fec_ctr

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2015 Google, Inc.
   4  *
   5  * Author: Sami Tolvanen <samitolvanen@google.com>
   6  */
   7 
   8 #include "dm-verity-fec.h"
   9 #include <linux/math64.h>
  10 
  11 #define DM_MSG_PREFIX   "verity-fec"
  12 
  13 /*
  14  * If error correction has been configured, returns true.
  15  */
  16 bool verity_fec_is_enabled(struct dm_verity *v)
  17 {
  18         return v->fec && v->fec->dev;
  19 }
  20 
  21 /*
  22  * Return a pointer to dm_verity_fec_io after dm_verity_io and its variable
  23  * length fields.
  24  */
  25 static inline struct dm_verity_fec_io *fec_io(struct dm_verity_io *io)
  26 {
  27         return (struct dm_verity_fec_io *) verity_io_digest_end(io->v, io);
  28 }
  29 
  30 /*
  31  * Return an interleaved offset for a byte in RS block.
  32  */
  33 static inline u64 fec_interleave(struct dm_verity *v, u64 offset)
  34 {
  35         u32 mod;
  36 
  37         mod = do_div(offset, v->fec->rsn);
  38         return offset + mod * (v->fec->rounds << v->data_dev_block_bits);
  39 }
  40 
  41 /*
  42  * Decode an RS block using Reed-Solomon.
  43  */
  44 static int fec_decode_rs8(struct dm_verity *v, struct dm_verity_fec_io *fio,
  45                           u8 *data, u8 *fec, int neras)
  46 {
  47         int i;
  48         uint16_t par[DM_VERITY_FEC_RSM - DM_VERITY_FEC_MIN_RSN];
  49 
  50         for (i = 0; i < v->fec->roots; i++)
  51                 par[i] = fec[i];
  52 
  53         return decode_rs8(fio->rs, data, par, v->fec->rsn, NULL, neras,
  54                           fio->erasures, 0, NULL);
  55 }
  56 
  57 /*
  58  * Read error-correcting codes for the requested RS block. Returns a pointer
  59  * to the data block. Caller is responsible for releasing buf.
  60  */
  61 static u8 *fec_read_parity(struct dm_verity *v, u64 rsb, int index,
  62                            unsigned *offset, struct dm_buffer **buf)
  63 {
  64         u64 position, block;
  65         u8 *res;
  66 
  67         position = (index + rsb) * v->fec->roots;
  68         block = position >> v->data_dev_block_bits;
  69         *offset = (unsigned)(position - (block << v->data_dev_block_bits));
  70 
  71         res = dm_bufio_read(v->fec->bufio, v->fec->start + block, buf);
  72         if (IS_ERR(res)) {
  73                 DMERR("%s: FEC %llu: parity read failed (block %llu): %ld",
  74                       v->data_dev->name, (unsigned long long)rsb,
  75                       (unsigned long long)(v->fec->start + block),
  76                       PTR_ERR(res));
  77                 *buf = NULL;
  78         }
  79 
  80         return res;
  81 }
  82 
  83 /* Loop over each preallocated buffer slot. */
  84 #define fec_for_each_prealloc_buffer(__i) \
  85         for (__i = 0; __i < DM_VERITY_FEC_BUF_PREALLOC; __i++)
  86 
  87 /* Loop over each extra buffer slot. */
  88 #define fec_for_each_extra_buffer(io, __i) \
  89         for (__i = DM_VERITY_FEC_BUF_PREALLOC; __i < DM_VERITY_FEC_BUF_MAX; __i++)
  90 
  91 /* Loop over each allocated buffer. */
  92 #define fec_for_each_buffer(io, __i) \
  93         for (__i = 0; __i < (io)->nbufs; __i++)
  94 
  95 /* Loop over each RS block in each allocated buffer. */
  96 #define fec_for_each_buffer_rs_block(io, __i, __j) \
  97         fec_for_each_buffer(io, __i) \
  98                 for (__j = 0; __j < 1 << DM_VERITY_FEC_BUF_RS_BITS; __j++)
  99 
 100 /*
 101  * Return a pointer to the current RS block when called inside
 102  * fec_for_each_buffer_rs_block.
 103  */
 104 static inline u8 *fec_buffer_rs_block(struct dm_verity *v,
 105                                       struct dm_verity_fec_io *fio,
 106                                       unsigned i, unsigned j)
 107 {
 108         return &fio->bufs[i][j * v->fec->rsn];
 109 }
 110 
 111 /*
 112  * Return an index to the current RS block when called inside
 113  * fec_for_each_buffer_rs_block.
 114  */
 115 static inline unsigned fec_buffer_rs_index(unsigned i, unsigned j)
 116 {
 117         return (i << DM_VERITY_FEC_BUF_RS_BITS) + j;
 118 }
 119 
 120 /*
 121  * Decode all RS blocks from buffers and copy corrected bytes into fio->output
 122  * starting from block_offset.
 123  */
 124 static int fec_decode_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio,
 125                            u64 rsb, int byte_index, unsigned block_offset,
 126                            int neras)
 127 {
 128         int r, corrected = 0, res;
 129         struct dm_buffer *buf;
 130         unsigned n, i, offset;
 131         u8 *par, *block;
 132 
 133         par = fec_read_parity(v, rsb, block_offset, &offset, &buf);
 134         if (IS_ERR(par))
 135                 return PTR_ERR(par);
 136 
 137         /*
 138          * Decode the RS blocks we have in bufs. Each RS block results in
 139          * one corrected target byte and consumes fec->roots parity bytes.
 140          */
 141         fec_for_each_buffer_rs_block(fio, n, i) {
 142                 block = fec_buffer_rs_block(v, fio, n, i);
 143                 res = fec_decode_rs8(v, fio, block, &par[offset], neras);
 144                 if (res < 0) {
 145                         r = res;
 146                         goto error;
 147                 }
 148 
 149                 corrected += res;
 150                 fio->output[block_offset] = block[byte_index];
 151 
 152                 block_offset++;
 153                 if (block_offset >= 1 << v->data_dev_block_bits)
 154                         goto done;
 155 
 156                 /* read the next block when we run out of parity bytes */
 157                 offset += v->fec->roots;
 158                 if (offset >= 1 << v->data_dev_block_bits) {
 159                         dm_bufio_release(buf);
 160 
 161                         par = fec_read_parity(v, rsb, block_offset, &offset, &buf);
 162                         if (IS_ERR(par))
 163                                 return PTR_ERR(par);
 164                 }
 165         }
 166 done:
 167         r = corrected;
 168 error:
 169         dm_bufio_release(buf);
 170 
 171         if (r < 0 && neras)
 172                 DMERR_LIMIT("%s: FEC %llu: failed to correct: %d",
 173                             v->data_dev->name, (unsigned long long)rsb, r);
 174         else if (r > 0)
 175                 DMWARN_LIMIT("%s: FEC %llu: corrected %d errors",
 176                              v->data_dev->name, (unsigned long long)rsb, r);
 177 
 178         return r;
 179 }
 180 
 181 /*
 182  * Locate data block erasures using verity hashes.
 183  */
 184 static int fec_is_erasure(struct dm_verity *v, struct dm_verity_io *io,
 185                           u8 *want_digest, u8 *data)
 186 {
 187         if (unlikely(verity_hash(v, verity_io_hash_req(v, io),
 188                                  data, 1 << v->data_dev_block_bits,
 189                                  verity_io_real_digest(v, io))))
 190                 return 0;
 191 
 192         return memcmp(verity_io_real_digest(v, io), want_digest,
 193                       v->digest_size) != 0;
 194 }
 195 
 196 /*
 197  * Read data blocks that are part of the RS block and deinterleave as much as
 198  * fits into buffers. Check for erasure locations if @neras is non-NULL.
 199  */
 200 static int fec_read_bufs(struct dm_verity *v, struct dm_verity_io *io,
 201                          u64 rsb, u64 target, unsigned block_offset,
 202                          int *neras)
 203 {
 204         bool is_zero;
 205         int i, j, target_index = -1;
 206         struct dm_buffer *buf;
 207         struct dm_bufio_client *bufio;
 208         struct dm_verity_fec_io *fio = fec_io(io);
 209         u64 block, ileaved;
 210         u8 *bbuf, *rs_block;
 211         u8 want_digest[HASH_MAX_DIGESTSIZE];
 212         unsigned n, k;
 213 
 214         if (neras)
 215                 *neras = 0;
 216 
 217         if (WARN_ON(v->digest_size > sizeof(want_digest)))
 218                 return -EINVAL;
 219 
 220         /*
 221          * read each of the rsn data blocks that are part of the RS block, and
 222          * interleave contents to available bufs
 223          */
 224         for (i = 0; i < v->fec->rsn; i++) {
 225                 ileaved = fec_interleave(v, rsb * v->fec->rsn + i);
 226 
 227                 /*
 228                  * target is the data block we want to correct, target_index is
 229                  * the index of this block within the rsn RS blocks
 230                  */
 231                 if (ileaved == target)
 232                         target_index = i;
 233 
 234                 block = ileaved >> v->data_dev_block_bits;
 235                 bufio = v->fec->data_bufio;
 236 
 237                 if (block >= v->data_blocks) {
 238                         block -= v->data_blocks;
 239 
 240                         /*
 241                          * blocks outside the area were assumed to contain
 242                          * zeros when encoding data was generated
 243                          */
 244                         if (unlikely(block >= v->fec->hash_blocks))
 245                                 continue;
 246 
 247                         block += v->hash_start;
 248                         bufio = v->bufio;
 249                 }
 250 
 251                 bbuf = dm_bufio_read(bufio, block, &buf);
 252                 if (IS_ERR(bbuf)) {
 253                         DMWARN_LIMIT("%s: FEC %llu: read failed (%llu): %ld",
 254                                      v->data_dev->name,
 255                                      (unsigned long long)rsb,
 256                                      (unsigned long long)block, PTR_ERR(bbuf));
 257 
 258                         /* assume the block is corrupted */
 259                         if (neras && *neras <= v->fec->roots)
 260                                 fio->erasures[(*neras)++] = i;
 261 
 262                         continue;
 263                 }
 264 
 265                 /* locate erasures if the block is on the data device */
 266                 if (bufio == v->fec->data_bufio &&
 267                     verity_hash_for_block(v, io, block, want_digest,
 268                                           &is_zero) == 0) {
 269                         /* skip known zero blocks entirely */
 270                         if (is_zero)
 271                                 goto done;
 272 
 273                         /*
 274                          * skip if we have already found the theoretical
 275                          * maximum number (i.e. fec->roots) of erasures
 276                          */
 277                         if (neras && *neras <= v->fec->roots &&
 278                             fec_is_erasure(v, io, want_digest, bbuf))
 279                                 fio->erasures[(*neras)++] = i;
 280                 }
 281 
 282                 /*
 283                  * deinterleave and copy the bytes that fit into bufs,
 284                  * starting from block_offset
 285                  */
 286                 fec_for_each_buffer_rs_block(fio, n, j) {
 287                         k = fec_buffer_rs_index(n, j) + block_offset;
 288 
 289                         if (k >= 1 << v->data_dev_block_bits)
 290                                 goto done;
 291 
 292                         rs_block = fec_buffer_rs_block(v, fio, n, j);
 293                         rs_block[i] = bbuf[k];
 294                 }
 295 done:
 296                 dm_bufio_release(buf);
 297         }
 298 
 299         return target_index;
 300 }
 301 
 302 /*
 303  * Allocate RS control structure and FEC buffers from preallocated mempools,
 304  * and attempt to allocate as many extra buffers as available.
 305  */
 306 static int fec_alloc_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio)
 307 {
 308         unsigned n;
 309 
 310         if (!fio->rs)
 311                 fio->rs = mempool_alloc(&v->fec->rs_pool, GFP_NOIO);
 312 
 313         fec_for_each_prealloc_buffer(n) {
 314                 if (fio->bufs[n])
 315                         continue;
 316 
 317                 fio->bufs[n] = mempool_alloc(&v->fec->prealloc_pool, GFP_NOWAIT);
 318                 if (unlikely(!fio->bufs[n])) {
 319                         DMERR("failed to allocate FEC buffer");
 320                         return -ENOMEM;
 321                 }
 322         }
 323 
 324         /* try to allocate the maximum number of buffers */
 325         fec_for_each_extra_buffer(fio, n) {
 326                 if (fio->bufs[n])
 327                         continue;
 328 
 329                 fio->bufs[n] = mempool_alloc(&v->fec->extra_pool, GFP_NOWAIT);
 330                 /* we can manage with even one buffer if necessary */
 331                 if (unlikely(!fio->bufs[n]))
 332                         break;
 333         }
 334         fio->nbufs = n;
 335 
 336         if (!fio->output)
 337                 fio->output = mempool_alloc(&v->fec->output_pool, GFP_NOIO);
 338 
 339         return 0;
 340 }
 341 
 342 /*
 343  * Initialize buffers and clear erasures. fec_read_bufs() assumes buffers are
 344  * zeroed before deinterleaving.
 345  */
 346 static void fec_init_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio)
 347 {
 348         unsigned n;
 349 
 350         fec_for_each_buffer(fio, n)
 351                 memset(fio->bufs[n], 0, v->fec->rsn << DM_VERITY_FEC_BUF_RS_BITS);
 352 
 353         memset(fio->erasures, 0, sizeof(fio->erasures));
 354 }
 355 
 356 /*
 357  * Decode all RS blocks in a single data block and return the target block
 358  * (indicated by @offset) in fio->output. If @use_erasures is non-zero, uses
 359  * hashes to locate erasures.
 360  */
 361 static int fec_decode_rsb(struct dm_verity *v, struct dm_verity_io *io,
 362                           struct dm_verity_fec_io *fio, u64 rsb, u64 offset,
 363                           bool use_erasures)
 364 {
 365         int r, neras = 0;
 366         unsigned pos;
 367 
 368         r = fec_alloc_bufs(v, fio);
 369         if (unlikely(r < 0))
 370                 return r;
 371 
 372         for (pos = 0; pos < 1 << v->data_dev_block_bits; ) {
 373                 fec_init_bufs(v, fio);
 374 
 375                 r = fec_read_bufs(v, io, rsb, offset, pos,
 376                                   use_erasures ? &neras : NULL);
 377                 if (unlikely(r < 0))
 378                         return r;
 379 
 380                 r = fec_decode_bufs(v, fio, rsb, r, pos, neras);
 381                 if (r < 0)
 382                         return r;
 383 
 384                 pos += fio->nbufs << DM_VERITY_FEC_BUF_RS_BITS;
 385         }
 386 
 387         /* Always re-validate the corrected block against the expected hash */
 388         r = verity_hash(v, verity_io_hash_req(v, io), fio->output,
 389                         1 << v->data_dev_block_bits,
 390                         verity_io_real_digest(v, io));
 391         if (unlikely(r < 0))
 392                 return r;
 393 
 394         if (memcmp(verity_io_real_digest(v, io), verity_io_want_digest(v, io),
 395                    v->digest_size)) {
 396                 DMERR_LIMIT("%s: FEC %llu: failed to correct (%d erasures)",
 397                             v->data_dev->name, (unsigned long long)rsb, neras);
 398                 return -EILSEQ;
 399         }
 400 
 401         return 0;
 402 }
 403 
 404 static int fec_bv_copy(struct dm_verity *v, struct dm_verity_io *io, u8 *data,
 405                        size_t len)
 406 {
 407         struct dm_verity_fec_io *fio = fec_io(io);
 408 
 409         memcpy(data, &fio->output[fio->output_pos], len);
 410         fio->output_pos += len;
 411 
 412         return 0;
 413 }
 414 
 415 /*
 416  * Correct errors in a block. Copies corrected block to dest if non-NULL,
 417  * otherwise to a bio_vec starting from iter.
 418  */
 419 int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io,
 420                       enum verity_block_type type, sector_t block, u8 *dest,
 421                       struct bvec_iter *iter)
 422 {
 423         int r;
 424         struct dm_verity_fec_io *fio = fec_io(io);
 425         u64 offset, res, rsb;
 426 
 427         if (!verity_fec_is_enabled(v))
 428                 return -EOPNOTSUPP;
 429 
 430         if (fio->level >= DM_VERITY_FEC_MAX_RECURSION) {
 431                 DMWARN_LIMIT("%s: FEC: recursion too deep", v->data_dev->name);
 432                 return -EIO;
 433         }
 434 
 435         fio->level++;
 436 
 437         if (type == DM_VERITY_BLOCK_TYPE_METADATA)
 438                 block = block - v->hash_start + v->data_blocks;
 439 
 440         /*
 441          * For RS(M, N), the continuous FEC data is divided into blocks of N
 442          * bytes. Since block size may not be divisible by N, the last block
 443          * is zero padded when decoding.
 444          *
 445          * Each byte of the block is covered by a different RS(M, N) code,
 446          * and each code is interleaved over N blocks to make it less likely
 447          * that bursty corruption will leave us in unrecoverable state.
 448          */
 449 
 450         offset = block << v->data_dev_block_bits;
 451         res = div64_u64(offset, v->fec->rounds << v->data_dev_block_bits);
 452 
 453         /*
 454          * The base RS block we can feed to the interleaver to find out all
 455          * blocks required for decoding.
 456          */
 457         rsb = offset - res * (v->fec->rounds << v->data_dev_block_bits);
 458 
 459         /*
 460          * Locating erasures is slow, so attempt to recover the block without
 461          * them first. Do a second attempt with erasures if the corruption is
 462          * bad enough.
 463          */
 464         r = fec_decode_rsb(v, io, fio, rsb, offset, false);
 465         if (r < 0) {
 466                 r = fec_decode_rsb(v, io, fio, rsb, offset, true);
 467                 if (r < 0)
 468                         goto done;
 469         }
 470 
 471         if (dest)
 472                 memcpy(dest, fio->output, 1 << v->data_dev_block_bits);
 473         else if (iter) {
 474                 fio->output_pos = 0;
 475                 r = verity_for_bv_block(v, io, iter, fec_bv_copy);
 476         }
 477 
 478 done:
 479         fio->level--;
 480         return r;
 481 }
 482 
 483 /*
 484  * Clean up per-bio data.
 485  */
 486 void verity_fec_finish_io(struct dm_verity_io *io)
 487 {
 488         unsigned n;
 489         struct dm_verity_fec *f = io->v->fec;
 490         struct dm_verity_fec_io *fio = fec_io(io);
 491 
 492         if (!verity_fec_is_enabled(io->v))
 493                 return;
 494 
 495         mempool_free(fio->rs, &f->rs_pool);
 496 
 497         fec_for_each_prealloc_buffer(n)
 498                 mempool_free(fio->bufs[n], &f->prealloc_pool);
 499 
 500         fec_for_each_extra_buffer(fio, n)
 501                 mempool_free(fio->bufs[n], &f->extra_pool);
 502 
 503         mempool_free(fio->output, &f->output_pool);
 504 }
 505 
 506 /*
 507  * Initialize per-bio data.
 508  */
 509 void verity_fec_init_io(struct dm_verity_io *io)
 510 {
 511         struct dm_verity_fec_io *fio = fec_io(io);
 512 
 513         if (!verity_fec_is_enabled(io->v))
 514                 return;
 515 
 516         fio->rs = NULL;
 517         memset(fio->bufs, 0, sizeof(fio->bufs));
 518         fio->nbufs = 0;
 519         fio->output = NULL;
 520         fio->level = 0;
 521 }
 522 
 523 /*
 524  * Append feature arguments and values to the status table.
 525  */
 526 unsigned verity_fec_status_table(struct dm_verity *v, unsigned sz,
 527                                  char *result, unsigned maxlen)
 528 {
 529         if (!verity_fec_is_enabled(v))
 530                 return sz;
 531 
 532         DMEMIT(" " DM_VERITY_OPT_FEC_DEV " %s "
 533                DM_VERITY_OPT_FEC_BLOCKS " %llu "
 534                DM_VERITY_OPT_FEC_START " %llu "
 535                DM_VERITY_OPT_FEC_ROOTS " %d",
 536                v->fec->dev->name,
 537                (unsigned long long)v->fec->blocks,
 538                (unsigned long long)v->fec->start,
 539                v->fec->roots);
 540 
 541         return sz;
 542 }
 543 
 544 void verity_fec_dtr(struct dm_verity *v)
 545 {
 546         struct dm_verity_fec *f = v->fec;
 547 
 548         if (!verity_fec_is_enabled(v))
 549                 goto out;
 550 
 551         mempool_exit(&f->rs_pool);
 552         mempool_exit(&f->prealloc_pool);
 553         mempool_exit(&f->extra_pool);
 554         mempool_exit(&f->output_pool);
 555         kmem_cache_destroy(f->cache);
 556 
 557         if (f->data_bufio)
 558                 dm_bufio_client_destroy(f->data_bufio);
 559         if (f->bufio)
 560                 dm_bufio_client_destroy(f->bufio);
 561 
 562         if (f->dev)
 563                 dm_put_device(v->ti, f->dev);
 564 out:
 565         kfree(f);
 566         v->fec = NULL;
 567 }
 568 
 569 static void *fec_rs_alloc(gfp_t gfp_mask, void *pool_data)
 570 {
 571         struct dm_verity *v = (struct dm_verity *)pool_data;
 572 
 573         return init_rs_gfp(8, 0x11d, 0, 1, v->fec->roots, gfp_mask);
 574 }
 575 
 576 static void fec_rs_free(void *element, void *pool_data)
 577 {
 578         struct rs_control *rs = (struct rs_control *)element;
 579 
 580         if (rs)
 581                 free_rs(rs);
 582 }
 583 
 584 bool verity_is_fec_opt_arg(const char *arg_name)
 585 {
 586         return (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_DEV) ||
 587                 !strcasecmp(arg_name, DM_VERITY_OPT_FEC_BLOCKS) ||
 588                 !strcasecmp(arg_name, DM_VERITY_OPT_FEC_START) ||
 589                 !strcasecmp(arg_name, DM_VERITY_OPT_FEC_ROOTS));
 590 }
 591 
 592 int verity_fec_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
 593                               unsigned *argc, const char *arg_name)
 594 {
 595         int r;
 596         struct dm_target *ti = v->ti;
 597         const char *arg_value;
 598         unsigned long long num_ll;
 599         unsigned char num_c;
 600         char dummy;
 601 
 602         if (!*argc) {
 603                 ti->error = "FEC feature arguments require a value";
 604                 return -EINVAL;
 605         }
 606 
 607         arg_value = dm_shift_arg(as);
 608         (*argc)--;
 609 
 610         if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_DEV)) {
 611                 r = dm_get_device(ti, arg_value, FMODE_READ, &v->fec->dev);
 612                 if (r) {
 613                         ti->error = "FEC device lookup failed";
 614                         return r;
 615                 }
 616 
 617         } else if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_BLOCKS)) {
 618                 if (sscanf(arg_value, "%llu%c", &num_ll, &dummy) != 1 ||
 619                     ((sector_t)(num_ll << (v->data_dev_block_bits - SECTOR_SHIFT))
 620                      >> (v->data_dev_block_bits - SECTOR_SHIFT) != num_ll)) {
 621                         ti->error = "Invalid " DM_VERITY_OPT_FEC_BLOCKS;
 622                         return -EINVAL;
 623                 }
 624                 v->fec->blocks = num_ll;
 625 
 626         } else if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_START)) {
 627                 if (sscanf(arg_value, "%llu%c", &num_ll, &dummy) != 1 ||
 628                     ((sector_t)(num_ll << (v->data_dev_block_bits - SECTOR_SHIFT)) >>
 629                      (v->data_dev_block_bits - SECTOR_SHIFT) != num_ll)) {
 630                         ti->error = "Invalid " DM_VERITY_OPT_FEC_START;
 631                         return -EINVAL;
 632                 }
 633                 v->fec->start = num_ll;
 634 
 635         } else if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_ROOTS)) {
 636                 if (sscanf(arg_value, "%hhu%c", &num_c, &dummy) != 1 || !num_c ||
 637                     num_c < (DM_VERITY_FEC_RSM - DM_VERITY_FEC_MAX_RSN) ||
 638                     num_c > (DM_VERITY_FEC_RSM - DM_VERITY_FEC_MIN_RSN)) {
 639                         ti->error = "Invalid " DM_VERITY_OPT_FEC_ROOTS;
 640                         return -EINVAL;
 641                 }
 642                 v->fec->roots = num_c;
 643 
 644         } else {
 645                 ti->error = "Unrecognized verity FEC feature request";
 646                 return -EINVAL;
 647         }
 648 
 649         return 0;
 650 }
 651 
 652 /*
 653  * Allocate dm_verity_fec for v->fec. Must be called before verity_fec_ctr.
 654  */
 655 int verity_fec_ctr_alloc(struct dm_verity *v)
 656 {
 657         struct dm_verity_fec *f;
 658 
 659         f = kzalloc(sizeof(struct dm_verity_fec), GFP_KERNEL);
 660         if (!f) {
 661                 v->ti->error = "Cannot allocate FEC structure";
 662                 return -ENOMEM;
 663         }
 664         v->fec = f;
 665 
 666         return 0;
 667 }
 668 
 669 /*
 670  * Validate arguments and preallocate memory. Must be called after arguments
 671  * have been parsed using verity_fec_parse_opt_args.
 672  */
 673 int verity_fec_ctr(struct dm_verity *v)
 674 {
 675         struct dm_verity_fec *f = v->fec;
 676         struct dm_target *ti = v->ti;
 677         u64 hash_blocks;
 678         int ret;
 679 
 680         if (!verity_fec_is_enabled(v)) {
 681                 verity_fec_dtr(v);
 682                 return 0;
 683         }
 684 
 685         /*
 686          * FEC is computed over data blocks, possible metadata, and
 687          * hash blocks. In other words, FEC covers total of fec_blocks
 688          * blocks consisting of the following:
 689          *
 690          *  data blocks | hash blocks | metadata (optional)
 691          *
 692          * We allow metadata after hash blocks to support a use case
 693          * where all data is stored on the same device and FEC covers
 694          * the entire area.
 695          *
 696          * If metadata is included, we require it to be available on the
 697          * hash device after the hash blocks.
 698          */
 699 
 700         hash_blocks = v->hash_blocks - v->hash_start;
 701 
 702         /*
 703          * Require matching block sizes for data and hash devices for
 704          * simplicity.
 705          */
 706         if (v->data_dev_block_bits != v->hash_dev_block_bits) {
 707                 ti->error = "Block sizes must match to use FEC";
 708                 return -EINVAL;
 709         }
 710 
 711         if (!f->roots) {
 712                 ti->error = "Missing " DM_VERITY_OPT_FEC_ROOTS;
 713                 return -EINVAL;
 714         }
 715         f->rsn = DM_VERITY_FEC_RSM - f->roots;
 716 
 717         if (!f->blocks) {
 718                 ti->error = "Missing " DM_VERITY_OPT_FEC_BLOCKS;
 719                 return -EINVAL;
 720         }
 721 
 722         f->rounds = f->blocks;
 723         if (sector_div(f->rounds, f->rsn))
 724                 f->rounds++;
 725 
 726         /*
 727          * Due to optional metadata, f->blocks can be larger than
 728          * data_blocks and hash_blocks combined.
 729          */
 730         if (f->blocks < v->data_blocks + hash_blocks || !f->rounds) {
 731                 ti->error = "Invalid " DM_VERITY_OPT_FEC_BLOCKS;
 732                 return -EINVAL;
 733         }
 734 
 735         /*
 736          * Metadata is accessed through the hash device, so we require
 737          * it to be large enough.
 738          */
 739         f->hash_blocks = f->blocks - v->data_blocks;
 740         if (dm_bufio_get_device_size(v->bufio) < f->hash_blocks) {
 741                 ti->error = "Hash device is too small for "
 742                         DM_VERITY_OPT_FEC_BLOCKS;
 743                 return -E2BIG;
 744         }
 745 
 746         f->bufio = dm_bufio_client_create(f->dev->bdev,
 747                                           1 << v->data_dev_block_bits,
 748                                           1, 0, NULL, NULL);
 749         if (IS_ERR(f->bufio)) {
 750                 ti->error = "Cannot initialize FEC bufio client";
 751                 return PTR_ERR(f->bufio);
 752         }
 753 
 754         if (dm_bufio_get_device_size(f->bufio) <
 755             ((f->start + f->rounds * f->roots) >> v->data_dev_block_bits)) {
 756                 ti->error = "FEC device is too small";
 757                 return -E2BIG;
 758         }
 759 
 760         f->data_bufio = dm_bufio_client_create(v->data_dev->bdev,
 761                                                1 << v->data_dev_block_bits,
 762                                                1, 0, NULL, NULL);
 763         if (IS_ERR(f->data_bufio)) {
 764                 ti->error = "Cannot initialize FEC data bufio client";
 765                 return PTR_ERR(f->data_bufio);
 766         }
 767 
 768         if (dm_bufio_get_device_size(f->data_bufio) < v->data_blocks) {
 769                 ti->error = "Data device is too small";
 770                 return -E2BIG;
 771         }
 772 
 773         /* Preallocate an rs_control structure for each worker thread */
 774         ret = mempool_init(&f->rs_pool, num_online_cpus(), fec_rs_alloc,
 775                            fec_rs_free, (void *) v);
 776         if (ret) {
 777                 ti->error = "Cannot allocate RS pool";
 778                 return ret;
 779         }
 780 
 781         f->cache = kmem_cache_create("dm_verity_fec_buffers",
 782                                      f->rsn << DM_VERITY_FEC_BUF_RS_BITS,
 783                                      0, 0, NULL);
 784         if (!f->cache) {
 785                 ti->error = "Cannot create FEC buffer cache";
 786                 return -ENOMEM;
 787         }
 788 
 789         /* Preallocate DM_VERITY_FEC_BUF_PREALLOC buffers for each thread */
 790         ret = mempool_init_slab_pool(&f->prealloc_pool, num_online_cpus() *
 791                                      DM_VERITY_FEC_BUF_PREALLOC,
 792                                      f->cache);
 793         if (ret) {
 794                 ti->error = "Cannot allocate FEC buffer prealloc pool";
 795                 return ret;
 796         }
 797 
 798         ret = mempool_init_slab_pool(&f->extra_pool, 0, f->cache);
 799         if (ret) {
 800                 ti->error = "Cannot allocate FEC buffer extra pool";
 801                 return ret;
 802         }
 803 
 804         /* Preallocate an output buffer for each thread */
 805         ret = mempool_init_kmalloc_pool(&f->output_pool, num_online_cpus(),
 806                                         1 << v->data_dev_block_bits);
 807         if (ret) {
 808                 ti->error = "Cannot allocate FEC output pool";
 809                 return ret;
 810         }
 811 
 812         /* Reserve space for our per-bio data */
 813         ti->per_io_data_size += sizeof(struct dm_verity_fec_io);
 814 
 815         return 0;
 816 }