lib/iov_iter.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #include <crypto/hash.h>
   3 #include <linux/export.h>
   4 #include <linux/bvec.h>
   5 #include <linux/fault-inject-usercopy.h>
   6 #include <linux/uio.h>
   7 #include <linux/pagemap.h>
   8 #include <linux/highmem.h>
   9 #include <linux/slab.h>
  10 #include <linux/vmalloc.h>
  11 #include <linux/splice.h>
  12 #include <linux/compat.h>
  13 #include <net/checksum.h>
  14 #include <linux/scatterlist.h>
  15 #include <linux/instrumented.h>
  16
  17 #define PIPE_PARANOIA /* for now */
  18
  19 /* covers iovec and kvec alike */
  20 #define iterate_iovec(i, n, base, len, off, __p, STEP) {        \
  21         size_t off = 0;                                         \
  22         size_t skip = i->iov_offset;                            \
  23         do {                                                    \
  24                 len = min(n, __p->iov_len - skip);              \
  25                 if (likely(len)) {                              \
  26                         base = __p->iov_base + skip;            \
  27                         len -= (STEP);                          \
  28                         off += len;                             \
  29                         skip += len;                            \
  30                         n -= len;                               \
  31                         if (skip < __p->iov_len)                \
  32                                 break;                          \
  33                 }                                               \
  34                 __p++;                                          \
  35                 skip = 0;                                       \
  36         } while (n);                                            \
  37         i->iov_offset = skip;                                   \
  38         n = off;                                                \
  39 }
  40
  41 #define iterate_bvec(i, n, base, len, off, p, STEP) {           \
  42         size_t off = 0;                                         \
  43         unsigned skip = i->iov_offset;                          \
  44         while (n) {                                             \
  45                 unsigned offset = p->bv_offset + skip;          \
  46                 unsigned left;                                  \
  47                 void *kaddr = kmap_local_page(p->bv_page +      \
  48                                         offset / PAGE_SIZE);    \
  49                 base = kaddr + offset % PAGE_SIZE;              \
  50                 len = min(min(n, (size_t)(p->bv_len - skip)),   \
  51                      (size_t)(PAGE_SIZE - offset % PAGE_SIZE)); \
  52                 left = (STEP);                                  \
  53                 kunmap_local(kaddr);                            \
  54                 len -= left;                                    \
  55                 off += len;                                     \
  56                 skip += len;                                    \
  57                 if (skip == p->bv_len) {                        \
  58                         skip = 0;                               \
  59                         p++;                                    \
  60                 }                                               \
  61                 n -= len;                                       \
  62                 if (left)                                       \
  63                         break;                                  \
  64         }                                                       \
  65         i->iov_offset = skip;                                   \
  66         n = off;                                                \
  67 }
  68
  69 #define iterate_xarray(i, n, base, len, __off, STEP) {          \
  70         __label__ __out;                                        \
  71         size_t __off = 0;                                       \
  72         struct page *head = NULL;                               \
  73         loff_t start = i->xarray_start + i->iov_offset;         \
  74         unsigned offset = start % PAGE_SIZE;                    \
  75         pgoff_t index = start / PAGE_SIZE;                      \
  76         int j;                                                  \
  77                                                                 \
  78         XA_STATE(xas, i->xarray, index);                        \
  79                                                                 \
  80         rcu_read_lock();                                        \
  81         xas_for_each(&xas, head, ULONG_MAX) {                   \
  82                 unsigned left;                                  \
  83                 if (xas_retry(&xas, head))                      \
  84                         continue;                               \
  85                 if (WARN_ON(xa_is_value(head)))                 \
  86                         break;                                  \
  87                 if (WARN_ON(PageHuge(head)))                    \
  88                         break;                                  \
  89                 for (j = (head->index < index) ? index - head->index : 0; \
  90                      j < thp_nr_pages(head); j++) {             \
  91                         void *kaddr = kmap_local_page(head + j);        \
  92                         base = kaddr + offset;                  \
  93                         len = PAGE_SIZE - offset;               \
  94                         len = min(n, len);                      \
  95                         left = (STEP);                          \
  96                         kunmap_local(kaddr);                    \
  97                         len -= left;                            \
  98                         __off += len;                           \
  99                         n -= len;                               \
 100                         if (left || n == 0)                     \
 101                                 goto __out;                     \
 102                         offset = 0;                             \
 103                 }                                               \
 104         }                                                       \
 105 __out:                                                          \
 106         rcu_read_unlock();                                      \
 107         i->iov_offset += __off;                                         \
 108         n = __off;                                              \
 109 }
 110
 111 #define __iterate_and_advance(i, n, base, len, off, I, K) {     \
 112         if (unlikely(i->count < n))                             \
 113                 n = i->count;                                   \
 114         if (likely(n)) {                                        \
 115                 if (likely(iter_is_iovec(i))) {                 \
 116                         const struct iovec *iov = i->iov;       \
 117                         void __user *base;                      \
 118                         size_t len;                             \
 119                         iterate_iovec(i, n, base, len, off,     \
 120                                                 iov, (I))       \
 121                         i->nr_segs -= iov - i->iov;             \
 122                         i->iov = iov;                           \
 123                 } else if (iov_iter_is_bvec(i)) {               \
 124                         const struct bio_vec *bvec = i->bvec;   \
 125                         void *base;                             \
 126                         size_t len;                             \
 127                         iterate_bvec(i, n, base, len, off,      \
 128                                                 bvec, (K))      \
 129                         i->nr_segs -= bvec - i->bvec;           \
 130                         i->bvec = bvec;                         \
 131                 } else if (iov_iter_is_kvec(i)) {               \
 132                         const struct kvec *kvec = i->kvec;      \
 133                         void *base;                             \
 134                         size_t len;                             \
 135                         iterate_iovec(i, n, base, len, off,     \
 136                                                 kvec, (K))      \
 137                         i->nr_segs -= kvec - i->kvec;           \
 138                         i->kvec = kvec;                         \
 139                 } else if (iov_iter_is_xarray(i)) {             \
 140                         void *base;                             \
 141                         size_t len;                             \
 142                         iterate_xarray(i, n, base, len, off,    \
 143                                                         (K))    \
 144                 }                                               \
 145                 i->count -= n;                                  \
 146         }                                                       \
 147 }
 148 #define iterate_and_advance(i, n, base, len, off, I, K) \
 149         __iterate_and_advance(i, n, base, len, off, I, ((void)(K),0))
 150
 151 static int copyout(void __user *to, const void *from, size_t n)
 152 {
 153         if (should_fail_usercopy())
 154                 return n;
 155         if (access_ok(to, n)) {
 156                 instrument_copy_to_user(to, from, n);
 157                 n = raw_copy_to_user(to, from, n);
 158         }
 159         return n;
 160 }
 161
 162 static int copyin(void *to, const void __user *from, size_t n)
 163 {
 164         if (should_fail_usercopy())
 165                 return n;
 166         if (access_ok(from, n)) {
 167                 instrument_copy_from_user(to, from, n);
 168                 n = raw_copy_from_user(to, from, n);
 169         }
 170         return n;
 171 }
 172
 173 static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t bytes,
 174                          struct iov_iter *i)
 175 {
 176         size_t skip, copy, left, wanted;
 177         const struct iovec *iov;
 178         char __user *buf;
 179         void *kaddr, *from;
 180
 181         if (unlikely(bytes > i->count))
 182                 bytes = i->count;
 183
 184         if (unlikely(!bytes))
 185                 return 0;
 186
 187         might_fault();
 188         wanted = bytes;
 189         iov = i->iov;
 190         skip = i->iov_offset;
 191         buf = iov->iov_base + skip;
 192         copy = min(bytes, iov->iov_len - skip);
 193
 194         if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_writeable(buf, copy)) {
 195                 kaddr = kmap_atomic(page);
 196                 from = kaddr + offset;
 197
 198                 /* first chunk, usually the only one */
 199                 left = copyout(buf, from, copy);
 200                 copy -= left;
 201                 skip += copy;
 202                 from += copy;
 203                 bytes -= copy;
 204
 205                 while (unlikely(!left && bytes)) {
 206                         iov++;
 207                         buf = iov->iov_base;
 208                         copy = min(bytes, iov->iov_len);
 209                         left = copyout(buf, from, copy);
 210                         copy -= left;
 211                         skip = copy;
 212                         from += copy;
 213                         bytes -= copy;
 214                 }
 215                 if (likely(!bytes)) {
 216                         kunmap_atomic(kaddr);
 217                         goto done;
 218                 }
 219                 offset = from - kaddr;
 220                 buf += copy;
 221                 kunmap_atomic(kaddr);
 222                 copy = min(bytes, iov->iov_len - skip);
 223         }
 224         /* Too bad - revert to non-atomic kmap */
 225
 226         kaddr = kmap(page);
 227         from = kaddr + offset;
 228         left = copyout(buf, from, copy);
 229         copy -= left;
 230         skip += copy;
 231         from += copy;
 232         bytes -= copy;
 233         while (unlikely(!left && bytes)) {
 234                 iov++;
 235                 buf = iov->iov_base;
 236                 copy = min(bytes, iov->iov_len);
 237                 left = copyout(buf, from, copy);
 238                 copy -= left;
 239                 skip = copy;
 240                 from += copy;
 241                 bytes -= copy;
 242         }
 243         kunmap(page);
 244
 245 done:
 246         if (skip == iov->iov_len) {
 247                 iov++;
 248                 skip = 0;
 249         }
 250         i->count -= wanted - bytes;
 251         i->nr_segs -= iov - i->iov;
 252         i->iov = iov;
 253         i->iov_offset = skip;
 254         return wanted - bytes;
 255 }
 256
 257 static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t bytes,
 258                          struct iov_iter *i)
 259 {
 260         size_t skip, copy, left, wanted;
 261         const struct iovec *iov;
 262         char __user *buf;
 263         void *kaddr, *to;
 264
 265         if (unlikely(bytes > i->count))
 266                 bytes = i->count;
 267
 268         if (unlikely(!bytes))
 269                 return 0;
 270
 271         might_fault();
 272         wanted = bytes;
 273         iov = i->iov;
 274         skip = i->iov_offset;
 275         buf = iov->iov_base + skip;
 276         copy = min(bytes, iov->iov_len - skip);
 277
 278         if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_readable(buf, copy)) {
 279                 kaddr = kmap_atomic(page);
 280                 to = kaddr + offset;
 281
 282                 /* first chunk, usually the only one */
 283                 left = copyin(to, buf, copy);
 284                 copy -= left;
 285                 skip += copy;
 286                 to += copy;
 287                 bytes -= copy;
 288
 289                 while (unlikely(!left && bytes)) {
 290                         iov++;
 291                         buf = iov->iov_base;
 292                         copy = min(bytes, iov->iov_len);
 293                         left = copyin(to, buf, copy);
 294                         copy -= left;
 295                         skip = copy;
 296                         to += copy;
 297                         bytes -= copy;
 298                 }
 299                 if (likely(!bytes)) {
 300                         kunmap_atomic(kaddr);
 301                         goto done;
 302                 }
 303                 offset = to - kaddr;
 304                 buf += copy;
 305                 kunmap_atomic(kaddr);
 306                 copy = min(bytes, iov->iov_len - skip);
 307         }
 308         /* Too bad - revert to non-atomic kmap */
 309
 310         kaddr = kmap(page);
 311         to = kaddr + offset;
 312         left = copyin(to, buf, copy);
 313         copy -= left;
 314         skip += copy;
 315         to += copy;
 316         bytes -= copy;
 317         while (unlikely(!left && bytes)) {
 318                 iov++;
 319                 buf = iov->iov_base;
 320                 copy = min(bytes, iov->iov_len);
 321                 left = copyin(to, buf, copy);
 322                 copy -= left;
 323                 skip = copy;
 324                 to += copy;
 325                 bytes -= copy;
 326         }
 327         kunmap(page);
 328
 329 done:
 330         if (skip == iov->iov_len) {
 331                 iov++;
 332                 skip = 0;
 333         }
 334         i->count -= wanted - bytes;
 335         i->nr_segs -= iov - i->iov;
 336         i->iov = iov;
 337         i->iov_offset = skip;
 338         return wanted - bytes;
 339 }
 340
 341 #ifdef PIPE_PARANOIA
 342 static bool sanity(const struct iov_iter *i)
 343 {
 344         struct pipe_inode_info *pipe = i->pipe;
 345         unsigned int p_head = pipe->head;
 346         unsigned int p_tail = pipe->tail;
 347         unsigned int p_mask = pipe->ring_size - 1;
 348         unsigned int p_occupancy = pipe_occupancy(p_head, p_tail);
 349         unsigned int i_head = i->head;
 350         unsigned int idx;
 351
 352         if (i->iov_offset) {
 353                 struct pipe_buffer *p;
 354                 if (unlikely(p_occupancy == 0))
 355                         goto Bad;       // pipe must be non-empty
 356                 if (unlikely(i_head != p_head - 1))
 357                         goto Bad;       // must be at the last buffer...
 358
 359                 p = &pipe->bufs[i_head & p_mask];
 360                 if (unlikely(p->offset + p->len != i->iov_offset))
 361                         goto Bad;       // ... at the end of segment
 362         } else {
 363                 if (i_head != p_head)
 364                         goto Bad;       // must be right after the last buffer
 365         }
 366         return true;
 367 Bad:
 368         printk(KERN_ERR "idx = %d, offset = %zd\n", i_head, i->iov_offset);
 369         printk(KERN_ERR "head = %d, tail = %d, buffers = %d\n",
 370                         p_head, p_tail, pipe->ring_size);
 371         for (idx = 0; idx < pipe->ring_size; idx++)
 372                 printk(KERN_ERR "[%p %p %d %d]\n",
 373                         pipe->bufs[idx].ops,
 374                         pipe->bufs[idx].page,
 375                         pipe->bufs[idx].offset,
 376                         pipe->bufs[idx].len);
 377         WARN_ON(1);
 378         return false;
 379 }
 380 #else
 381 #define sanity(i) true
 382 #endif
 383
 384 static size_t copy_page_to_iter_pipe(struct page *page, size_t offset, size_t bytes,
 385                          struct iov_iter *i)
 386 {
 387         struct pipe_inode_info *pipe = i->pipe;
 388         struct pipe_buffer *buf;
 389         unsigned int p_tail = pipe->tail;
 390         unsigned int p_mask = pipe->ring_size - 1;
 391         unsigned int i_head = i->head;
 392         size_t off;
 393
 394         if (unlikely(bytes > i->count))
 395                 bytes = i->count;
 396
 397         if (unlikely(!bytes))
 398                 return 0;
 399
 400         if (!sanity(i))
 401                 return 0;
 402
 403         off = i->iov_offset;
 404         buf = &pipe->bufs[i_head & p_mask];
 405         if (off) {
 406                 if (offset == off && buf->page == page) {
 407                         /* merge with the last one */
 408                         buf->len += bytes;
 409                         i->iov_offset += bytes;
 410                         goto out;
 411                 }
 412                 i_head++;
 413                 buf = &pipe->bufs[i_head & p_mask];
 414         }
 415         if (pipe_full(i_head, p_tail, pipe->max_usage))
 416                 return 0;
 417
 418         buf->ops = &page_cache_pipe_buf_ops;
 419         buf->flags = 0;
 420         get_page(page);
 421         buf->page = page;
 422         buf->offset = offset;
 423         buf->len = bytes;
 424
 425         pipe->head = i_head + 1;
 426         i->iov_offset = offset + bytes;
 427         i->head = i_head;
 428 out:
 429         i->count -= bytes;
 430         return bytes;
 431 }
 432
 433 /*
 434  * fault_in_iov_iter_readable - fault in iov iterator for reading
 435  * @i: iterator
 436  * @size: maximum length
 437  *
 438  * Fault in one or more iovecs of the given iov_iter, to a maximum length of
 439  * @size.  For each iovec, fault in each page that constitutes the iovec.
 440  *
 441  * Returns the number of bytes not faulted in (like copy_to_user() and
 442  * copy_from_user()).
 443  *
 444  * Always returns 0 for non-userspace iterators.
 445  */
 446 size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t size)
 447 {
 448         if (iter_is_iovec(i)) {
 449                 size_t count = min(size, iov_iter_count(i));
 450                 const struct iovec *p;
 451                 size_t skip;
 452
 453                 size -= count;
 454                 for (p = i->iov, skip = i->iov_offset; count; p++, skip = 0) {
 455                         size_t len = min(count, p->iov_len - skip);
 456                         size_t ret;
 457
 458                         if (unlikely(!len))
 459                                 continue;
 460                         ret = fault_in_readable(p->iov_base + skip, len);
 461                         count -= len - ret;
 462                         if (ret)
 463                                 break;
 464                 }
 465                 return count + size;
 466         }
 467         return 0;
 468 }
 469 EXPORT_SYMBOL(fault_in_iov_iter_readable);
 470
 471 /*
 472  * fault_in_iov_iter_writeable - fault in iov iterator for writing
 473  * @i: iterator
 474  * @size: maximum length
 475  *
 476  * Faults in the iterator using get_user_pages(), i.e., without triggering
 477  * hardware page faults.  This is primarily useful when we already know that
 478  * some or all of the pages in @i aren't in memory.
 479  *
 480  * Returns the number of bytes not faulted in, like copy_to_user() and
 481  * copy_from_user().
 482  *
 483  * Always returns 0 for non-user-space iterators.
 484  */
 485 size_t fault_in_iov_iter_writeable(const struct iov_iter *i, size_t size)
 486 {
 487         if (iter_is_iovec(i)) {
 488                 size_t count = min(size, iov_iter_count(i));
 489                 const struct iovec *p;
 490                 size_t skip;
 491
 492                 size -= count;
 493                 for (p = i->iov, skip = i->iov_offset; count; p++, skip = 0) {
 494                         size_t len = min(count, p->iov_len - skip);
 495                         size_t ret;
 496
 497                         if (unlikely(!len))
 498                                 continue;
 499                         ret = fault_in_safe_writeable(p->iov_base + skip, len);
 500                         count -= len - ret;
 501                         if (ret)
 502                                 break;
 503                 }
 504                 return count + size;
 505         }
 506         return 0;
 507 }
 508 EXPORT_SYMBOL(fault_in_iov_iter_writeable);
 509
 510 void iov_iter_init(struct iov_iter *i, unsigned int direction,
 511                         const struct iovec *iov, unsigned long nr_segs,
 512                         size_t count)
 513 {
 514         WARN_ON(direction & ~(READ | WRITE));
 515         *i = (struct iov_iter) {
 516                 .iter_type = ITER_IOVEC,
 517                 .nofault = false,
 518                 .data_source = direction,
 519                 .iov = iov,
 520                 .nr_segs = nr_segs,
 521                 .iov_offset = 0,
 522                 .count = count
 523         };
 524 }
 525 EXPORT_SYMBOL(iov_iter_init);
 526
 527 static inline bool allocated(struct pipe_buffer *buf)
 528 {
 529         return buf->ops == &default_pipe_buf_ops;
 530 }
 531
 532 static inline void data_start(const struct iov_iter *i,
 533                               unsigned int *iter_headp, size_t *offp)
 534 {
 535         unsigned int p_mask = i->pipe->ring_size - 1;
 536         unsigned int iter_head = i->head;
 537         size_t off = i->iov_offset;
 538
 539         if (off && (!allocated(&i->pipe->bufs[iter_head & p_mask]) ||
 540                     off == PAGE_SIZE)) {
 541                 iter_head++;
 542                 off = 0;
 543         }
 544         *iter_headp = iter_head;
 545         *offp = off;
 546 }
 547
 548 static size_t push_pipe(struct iov_iter *i, size_t size,
 549                         int *iter_headp, size_t *offp)
 550 {
 551         struct pipe_inode_info *pipe = i->pipe;
 552         unsigned int p_tail = pipe->tail;
 553         unsigned int p_mask = pipe->ring_size - 1;
 554         unsigned int iter_head;
 555         size_t off;
 556         ssize_t left;
 557
 558         if (unlikely(size > i->count))
 559                 size = i->count;
 560         if (unlikely(!size))
 561                 return 0;
 562
 563         left = size;
 564         data_start(i, &iter_head, &off);
 565         *iter_headp = iter_head;
 566         *offp = off;
 567         if (off) {
 568                 left -= PAGE_SIZE - off;
 569                 if (left <= 0) {
 570                         pipe->bufs[iter_head & p_mask].len += size;
 571                         return size;
 572                 }
 573                 pipe->bufs[iter_head & p_mask].len = PAGE_SIZE;
 574                 iter_head++;
 575         }
 576         while (!pipe_full(iter_head, p_tail, pipe->max_usage)) {
 577                 struct pipe_buffer *buf = &pipe->bufs[iter_head & p_mask];
 578                 struct page *page = alloc_page(GFP_USER);
 579                 if (!page)
 580                         break;
 581
 582                 buf->ops = &default_pipe_buf_ops;
 583                 buf->flags = 0;
 584                 buf->page = page;
 585                 buf->offset = 0;
 586                 buf->len = min_t(ssize_t, left, PAGE_SIZE);
 587                 left -= buf->len;
 588                 iter_head++;
 589                 pipe->head = iter_head;
 590
 591                 if (left == 0)
 592                         return size;
 593         }
 594         return size - left;
 595 }
 596
 597 static size_t copy_pipe_to_iter(const void *addr, size_t bytes,
 598                                 struct iov_iter *i)
 599 {
 600         struct pipe_inode_info *pipe = i->pipe;
 601         unsigned int p_mask = pipe->ring_size - 1;
 602         unsigned int i_head;
 603         size_t n, off;
 604
 605         if (!sanity(i))
 606                 return 0;
 607
 608         bytes = n = push_pipe(i, bytes, &i_head, &off);
 609         if (unlikely(!n))
 610                 return 0;
 611         do {
 612                 size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
 613                 memcpy_to_page(pipe->bufs[i_head & p_mask].page, off, addr, chunk);
 614                 i->head = i_head;
 615                 i->iov_offset = off + chunk;
 616                 n -= chunk;
 617                 addr += chunk;
 618                 off = 0;
 619                 i_head++;
 620         } while (n);
 621         i->count -= bytes;
 622         return bytes;
 623 }
 624
 625 static __wsum csum_and_memcpy(void *to, const void *from, size_t len,
 626                               __wsum sum, size_t off)
 627 {
 628         __wsum next = csum_partial_copy_nocheck(from, to, len);
 629         return csum_block_add(sum, next, off);
 630 }
 631
 632 static size_t csum_and_copy_to_pipe_iter(const void *addr, size_t bytes,
 633                                          struct iov_iter *i, __wsum *sump)
 634 {
 635         struct pipe_inode_info *pipe = i->pipe;
 636         unsigned int p_mask = pipe->ring_size - 1;
 637         __wsum sum = *sump;
 638         size_t off = 0;
 639         unsigned int i_head;
 640         size_t r;
 641
 642         if (!sanity(i))
 643                 return 0;
 644
 645         bytes = push_pipe(i, bytes, &i_head, &r);
 646         while (bytes) {
 647                 size_t chunk = min_t(size_t, bytes, PAGE_SIZE - r);
 648                 char *p = kmap_local_page(pipe->bufs[i_head & p_mask].page);
 649                 sum = csum_and_memcpy(p + r, addr + off, chunk, sum, off);
 650                 kunmap_local(p);
 651                 i->head = i_head;
 652                 i->iov_offset = r + chunk;
 653                 bytes -= chunk;
 654                 off += chunk;
 655                 r = 0;
 656                 i_head++;
 657         }
 658         *sump = sum;
 659         i->count -= off;
 660         return off;
 661 }
 662
 663 size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 664 {
 665         if (unlikely(iov_iter_is_pipe(i)))
 666                 return copy_pipe_to_iter(addr, bytes, i);
 667         if (iter_is_iovec(i))
 668                 might_fault();
 669         iterate_and_advance(i, bytes, base, len, off,
 670                 copyout(base, addr + off, len),
 671                 memcpy(base, addr + off, len)
 672         )
 673
 674         return bytes;
 675 }
 676 EXPORT_SYMBOL(_copy_to_iter);
 677
 678 #ifdef CONFIG_ARCH_HAS_COPY_MC
 679 static int copyout_mc(void __user *to, const void *from, size_t n)
 680 {
 681         if (access_ok(to, n)) {
 682                 instrument_copy_to_user(to, from, n);
 683                 n = copy_mc_to_user((__force void *) to, from, n);
 684         }
 685         return n;
 686 }
 687
 688 static size_t copy_mc_pipe_to_iter(const void *addr, size_t bytes,
 689                                 struct iov_iter *i)
 690 {
 691         struct pipe_inode_info *pipe = i->pipe;
 692         unsigned int p_mask = pipe->ring_size - 1;
 693         unsigned int i_head;
 694         size_t n, off, xfer = 0;
 695
 696         if (!sanity(i))
 697                 return 0;
 698
 699         n = push_pipe(i, bytes, &i_head, &off);
 700         while (n) {
 701                 size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
 702                 char *p = kmap_local_page(pipe->bufs[i_head & p_mask].page);
 703                 unsigned long rem;
 704                 rem = copy_mc_to_kernel(p + off, addr + xfer, chunk);
 705                 chunk -= rem;
 706                 kunmap_local(p);
 707                 i->head = i_head;
 708                 i->iov_offset = off + chunk;
 709                 xfer += chunk;
 710                 if (rem)
 711                         break;
 712                 n -= chunk;
 713                 off = 0;
 714                 i_head++;
 715         }
 716         i->count -= xfer;
 717         return xfer;
 718 }
 719
 720 /**
 721  * _copy_mc_to_iter - copy to iter with source memory error exception handling
 722  * @addr: source kernel address
 723  * @bytes: total transfer length
 724  * @i: destination iterator
 725  *
 726  * The pmem driver deploys this for the dax operation
 727  * (dax_copy_to_iter()) for dax reads (bypass page-cache and the
 728  * block-layer). Upon #MC read(2) aborts and returns EIO or the bytes
 729  * successfully copied.
 730  *
 731  * The main differences between this and typical _copy_to_iter().
 732  *
 733  * * Typical tail/residue handling after a fault retries the copy
 734  *   byte-by-byte until the fault happens again. Re-triggering machine
 735  *   checks is potentially fatal so the implementation uses source
 736  *   alignment and poison alignment assumptions to avoid re-triggering
 737  *   hardware exceptions.
 738  *
 739  * * ITER_KVEC, ITER_PIPE, and ITER_BVEC can return short copies.
 740  *   Compare to copy_to_iter() where only ITER_IOVEC attempts might return
 741  *   a short copy.
 742  *
 743  * Return: number of bytes copied (may be %0)
 744  */
 745 size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 746 {
 747         if (unlikely(iov_iter_is_pipe(i)))
 748                 return copy_mc_pipe_to_iter(addr, bytes, i);
 749         if (iter_is_iovec(i))
 750                 might_fault();
 751         __iterate_and_advance(i, bytes, base, len, off,
 752                 copyout_mc(base, addr + off, len),
 753                 copy_mc_to_kernel(base, addr + off, len)
 754         )
 755
 756         return bytes;
 757 }
 758 EXPORT_SYMBOL_GPL(_copy_mc_to_iter);
 759 #endif /* CONFIG_ARCH_HAS_COPY_MC */
 760
 761 size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
 762 {
 763         if (unlikely(iov_iter_is_pipe(i))) {
 764                 WARN_ON(1);
 765                 return 0;
 766         }
 767         if (iter_is_iovec(i))
 768                 might_fault();
 769         iterate_and_advance(i, bytes, base, len, off,
 770                 copyin(addr + off, base, len),
 771                 memcpy(addr + off, base, len)
 772         )
 773
 774         return bytes;
 775 }
 776 EXPORT_SYMBOL(_copy_from_iter);
 777
 778 size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)
 779 {
 780         if (unlikely(iov_iter_is_pipe(i))) {
 781                 WARN_ON(1);
 782                 return 0;
 783         }
 784         iterate_and_advance(i, bytes, base, len, off,
 785                 __copy_from_user_inatomic_nocache(addr + off, base, len),
 786                 memcpy(addr + off, base, len)
 787         )
 788
 789         return bytes;
 790 }
 791 EXPORT_SYMBOL(_copy_from_iter_nocache);
 792
 793 #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
 794 /**
 795  * _copy_from_iter_flushcache - write destination through cpu cache
 796  * @addr: destination kernel address
 797  * @bytes: total transfer length
 798  * @i: source iterator
 799  *
 800  * The pmem driver arranges for filesystem-dax to use this facility via
 801  * dax_copy_from_iter() for ensuring that writes to persistent memory
 802  * are flushed through the CPU cache. It is differentiated from
 803  * _copy_from_iter_nocache() in that guarantees all data is flushed for
 804  * all iterator types. The _copy_from_iter_nocache() only attempts to
 805  * bypass the cache for the ITER_IOVEC case, and on some archs may use
 806  * instructions that strand dirty-data in the cache.
 807  *
 808  * Return: number of bytes copied (may be %0)
 809  */
 810 size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i)
 811 {
 812         if (unlikely(iov_iter_is_pipe(i))) {
 813                 WARN_ON(1);
 814                 return 0;
 815         }
 816         iterate_and_advance(i, bytes, base, len, off,
 817                 __copy_from_user_flushcache(addr + off, base, len),
 818                 memcpy_flushcache(addr + off, base, len)
 819         )
 820
 821         return bytes;
 822 }
 823 EXPORT_SYMBOL_GPL(_copy_from_iter_flushcache);
 824 #endif
 825
 826 static inline bool page_copy_sane(struct page *page, size_t offset, size_t n)
 827 {
 828         struct page *head;
 829         size_t v = n + offset;
 830
 831         /*
 832          * The general case needs to access the page order in order
 833          * to compute the page size.
 834          * However, we mostly deal with order-0 pages and thus can
 835          * avoid a possible cache line miss for requests that fit all
 836          * page orders.
 837          */
 838         if (n <= v && v <= PAGE_SIZE)
 839                 return true;
 840
 841         head = compound_head(page);
 842         v += (page - head) << PAGE_SHIFT;
 843
 844         if (likely(n <= v && v <= (page_size(head))))
 845                 return true;
 846         WARN_ON(1);
 847         return false;
 848 }
 849
 850 static size_t __copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
 851                          struct iov_iter *i)
 852 {
 853         if (likely(iter_is_iovec(i)))
 854                 return copy_page_to_iter_iovec(page, offset, bytes, i);
 855         if (iov_iter_is_bvec(i) || iov_iter_is_kvec(i) || iov_iter_is_xarray(i)) {
 856                 void *kaddr = kmap_local_page(page);
 857                 size_t wanted = _copy_to_iter(kaddr + offset, bytes, i);
 858                 kunmap_local(kaddr);
 859                 return wanted;
 860         }
 861         if (iov_iter_is_pipe(i))
 862                 return copy_page_to_iter_pipe(page, offset, bytes, i);
 863         if (unlikely(iov_iter_is_discard(i))) {
 864                 if (unlikely(i->count < bytes))
 865                         bytes = i->count;
 866                 i->count -= bytes;
 867                 return bytes;
 868         }
 869         WARN_ON(1);
 870         return 0;
 871 }
 872
 873 size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
 874                          struct iov_iter *i)
 875 {
 876         size_t res = 0;
 877         if (unlikely(!page_copy_sane(page, offset, bytes)))
 878                 return 0;
 879         page += offset / PAGE_SIZE; // first subpage
 880         offset %= PAGE_SIZE;
 881         while (1) {
 882                 size_t n = __copy_page_to_iter(page, offset,
 883                                 min(bytes, (size_t)PAGE_SIZE - offset), i);
 884                 res += n;
 885                 bytes -= n;
 886                 if (!bytes || !n)
 887                         break;
 888                 offset += n;
 889                 if (offset == PAGE_SIZE) {
 890                         page++;
 891                         offset = 0;
 892                 }
 893         }
 894         return res;
 895 }
 896 EXPORT_SYMBOL(copy_page_to_iter);
 897
 898 size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
 899                          struct iov_iter *i)
 900 {
 901         if (unlikely(!page_copy_sane(page, offset, bytes)))
 902                 return 0;
 903         if (likely(iter_is_iovec(i)))
 904                 return copy_page_from_iter_iovec(page, offset, bytes, i);
 905         if (iov_iter_is_bvec(i) || iov_iter_is_kvec(i) || iov_iter_is_xarray(i)) {
 906                 void *kaddr = kmap_local_page(page);
 907                 size_t wanted = _copy_from_iter(kaddr + offset, bytes, i);
 908                 kunmap_local(kaddr);
 909                 return wanted;
 910         }
 911         WARN_ON(1);
 912         return 0;
 913 }
 914 EXPORT_SYMBOL(copy_page_from_iter);
 915
 916 static size_t pipe_zero(size_t bytes, struct iov_iter *i)
 917 {
 918         struct pipe_inode_info *pipe = i->pipe;
 919         unsigned int p_mask = pipe->ring_size - 1;
 920         unsigned int i_head;
 921         size_t n, off;
 922
 923         if (!sanity(i))
 924                 return 0;
 925
 926         bytes = n = push_pipe(i, bytes, &i_head, &off);
 927         if (unlikely(!n))
 928                 return 0;
 929
 930         do {
 931                 size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
 932                 char *p = kmap_local_page(pipe->bufs[i_head & p_mask].page);
 933                 memset(p + off, 0, chunk);
 934                 kunmap_local(p);
 935                 i->head = i_head;
 936                 i->iov_offset = off + chunk;
 937                 n -= chunk;
 938                 off = 0;
 939                 i_head++;
 940         } while (n);
 941         i->count -= bytes;
 942         return bytes;
 943 }
 944
 945 size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
 946 {
 947         if (unlikely(iov_iter_is_pipe(i)))
 948                 return pipe_zero(bytes, i);
 949         iterate_and_advance(i, bytes, base, len, count,
 950                 clear_user(base, len),
 951                 memset(base, 0, len)
 952         )
 953
 954         return bytes;
 955 }
 956 EXPORT_SYMBOL(iov_iter_zero);
 957
 958 size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, size_t bytes,
 959                                   struct iov_iter *i)
 960 {
 961         char *kaddr = kmap_atomic(page), *p = kaddr + offset;
 962         if (unlikely(!page_copy_sane(page, offset, bytes))) {
 963                 kunmap_atomic(kaddr);
 964                 return 0;
 965         }
 966         if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {
 967                 kunmap_atomic(kaddr);
 968                 WARN_ON(1);
 969                 return 0;
 970         }
 971         iterate_and_advance(i, bytes, base, len, off,
 972                 copyin(p + off, base, len),
 973                 memcpy(p + off, base, len)
 974         )
 975         kunmap_atomic(kaddr);
 976         return bytes;
 977 }
 978 EXPORT_SYMBOL(copy_page_from_iter_atomic);
 979
 980 static inline void pipe_truncate(struct iov_iter *i)
 981 {
 982         struct pipe_inode_info *pipe = i->pipe;
 983         unsigned int p_tail = pipe->tail;
 984         unsigned int p_head = pipe->head;
 985         unsigned int p_mask = pipe->ring_size - 1;
 986
 987         if (!pipe_empty(p_head, p_tail)) {
 988                 struct pipe_buffer *buf;
 989                 unsigned int i_head = i->head;
 990                 size_t off = i->iov_offset;
 991
 992                 if (off) {
 993                         buf = &pipe->bufs[i_head & p_mask];
 994                         buf->len = off - buf->offset;
 995                         i_head++;
 996                 }
 997                 while (p_head != i_head) {
 998                         p_head--;
 999                         pipe_buf_release(pipe, &pipe->bufs[p_head & p_mask]);
1000                 }
1001
1002                 pipe->head = p_head;
1003         }
1004 }
1005
1006 static void pipe_advance(struct iov_iter *i, size_t size)
1007 {
1008         struct pipe_inode_info *pipe = i->pipe;
1009         if (size) {
1010                 struct pipe_buffer *buf;
1011                 unsigned int p_mask = pipe->ring_size - 1;
1012                 unsigned int i_head = i->head;
1013                 size_t off = i->iov_offset, left = size;
1014
1015                 if (off) /* make it relative to the beginning of buffer */
1016                         left += off - pipe->bufs[i_head & p_mask].offset;
1017                 while (1) {
1018                         buf = &pipe->bufs[i_head & p_mask];
1019                         if (left <= buf->len)
1020                                 break;
1021                         left -= buf->len;
1022                         i_head++;
1023                 }
1024                 i->head = i_head;
1025                 i->iov_offset = buf->offset + left;
1026         }
1027         i->count -= size;
1028         /* ... and discard everything past that point */
1029         pipe_truncate(i);
1030 }
1031
1032 static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)
1033 {
1034         struct bvec_iter bi;
1035
1036         bi.bi_size = i->count;
1037         bi.bi_bvec_done = i->iov_offset;
1038         bi.bi_idx = 0;
1039         bvec_iter_advance(i->bvec, &bi, size);
1040
1041         i->bvec += bi.bi_idx;
1042         i->nr_segs -= bi.bi_idx;
1043         i->count = bi.bi_size;
1044         i->iov_offset = bi.bi_bvec_done;
1045 }
1046
1047 static void iov_iter_iovec_advance(struct iov_iter *i, size_t size)
1048 {
1049         const struct iovec *iov, *end;
1050
1051         if (!i->count)
1052                 return;
1053         i->count -= size;
1054
1055         size += i->iov_offset; // from beginning of current segment
1056         for (iov = i->iov, end = iov + i->nr_segs; iov < end; iov++) {
1057                 if (likely(size < iov->iov_len))
1058                         break;
1059                 size -= iov->iov_len;
1060         }
1061         i->iov_offset = size;
1062         i->nr_segs -= iov - i->iov;
1063         i->iov = iov;
1064 }
1065
1066 void iov_iter_advance(struct iov_iter *i, size_t size)
1067 {
1068         if (unlikely(i->count < size))
1069                 size = i->count;
1070         if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i))) {
1071                 /* iovec and kvec have identical layouts */
1072                 iov_iter_iovec_advance(i, size);
1073         } else if (iov_iter_is_bvec(i)) {
1074                 iov_iter_bvec_advance(i, size);
1075         } else if (iov_iter_is_pipe(i)) {
1076                 pipe_advance(i, size);
1077         } else if (unlikely(iov_iter_is_xarray(i))) {
1078                 i->iov_offset += size;
1079                 i->count -= size;
1080         } else if (iov_iter_is_discard(i)) {
1081                 i->count -= size;
1082         }
1083 }
1084 EXPORT_SYMBOL(iov_iter_advance);
1085
1086 void iov_iter_revert(struct iov_iter *i, size_t unroll)
1087 {
1088         if (!unroll)
1089                 return;
1090         if (WARN_ON(unroll > MAX_RW_COUNT))
1091                 return;
1092         i->count += unroll;
1093         if (unlikely(iov_iter_is_pipe(i))) {
1094                 struct pipe_inode_info *pipe = i->pipe;
1095                 unsigned int p_mask = pipe->ring_size - 1;
1096                 unsigned int i_head = i->head;
1097                 size_t off = i->iov_offset;
1098                 while (1) {
1099                         struct pipe_buffer *b = &pipe->bufs[i_head & p_mask];
1100                         size_t n = off - b->offset;
1101                         if (unroll < n) {
1102                                 off -= unroll;
1103                                 break;
1104                         }
1105                         unroll -= n;
1106                         if (!unroll && i_head == i->start_head) {
1107                                 off = 0;
1108                                 break;
1109                         }
1110                         i_head--;
1111                         b = &pipe->bufs[i_head & p_mask];
1112                         off = b->offset + b->len;
1113                 }
1114                 i->iov_offset = off;
1115                 i->head = i_head;
1116                 pipe_truncate(i);
1117                 return;
1118         }
1119         if (unlikely(iov_iter_is_discard(i)))
1120                 return;
1121         if (unroll <= i->iov_offset) {
1122                 i->iov_offset -= unroll;
1123                 return;
1124         }
1125         unroll -= i->iov_offset;
1126         if (iov_iter_is_xarray(i)) {
1127                 BUG(); /* We should never go beyond the start of the specified
1128                         * range since we might then be straying into pages that
1129                         * aren't pinned.
1130                         */
1131         } else if (iov_iter_is_bvec(i)) {
1132                 const struct bio_vec *bvec = i->bvec;
1133                 while (1) {
1134                         size_t n = (--bvec)->bv_len;
1135                         i->nr_segs++;
1136                         if (unroll <= n) {
1137                                 i->bvec = bvec;
1138                                 i->iov_offset = n - unroll;
1139                                 return;
1140                         }
1141                         unroll -= n;
1142                 }
1143         } else { /* same logics for iovec and kvec */
1144                 const struct iovec *iov = i->iov;
1145                 while (1) {
1146                         size_t n = (--iov)->iov_len;
1147                         i->nr_segs++;
1148                         if (unroll <= n) {
1149                                 i->iov = iov;
1150                                 i->iov_offset = n - unroll;
1151                                 return;
1152                         }
1153                         unroll -= n;
1154                 }
1155         }
1156 }
1157 EXPORT_SYMBOL(iov_iter_revert);
1158
1159 /*
1160  * Return the count of just the current iov_iter segment.
1161  */
1162 size_t iov_iter_single_seg_count(const struct iov_iter *i)
1163 {
1164         if (i->nr_segs > 1) {
1165                 if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
1166                         return min(i->count, i->iov->iov_len - i->iov_offset);
1167                 if (iov_iter_is_bvec(i))
1168                         return min(i->count, i->bvec->bv_len - i->iov_offset);
1169         }
1170         return i->count;
1171 }
1172 EXPORT_SYMBOL(iov_iter_single_seg_count);
1173
1174 void iov_iter_kvec(struct iov_iter *i, unsigned int direction,
1175                         const struct kvec *kvec, unsigned long nr_segs,
1176                         size_t count)
1177 {
1178         WARN_ON(direction & ~(READ | WRITE));
1179         *i = (struct iov_iter){
1180                 .iter_type = ITER_KVEC,
1181                 .data_source = direction,
1182                 .kvec = kvec,
1183                 .nr_segs = nr_segs,
1184                 .iov_offset = 0,
1185                 .count = count
1186         };
1187 }
1188 EXPORT_SYMBOL(iov_iter_kvec);
1189
1190 void iov_iter_bvec(struct iov_iter *i, unsigned int direction,
1191                         const struct bio_vec *bvec, unsigned long nr_segs,
1192                         size_t count)
1193 {
1194         WARN_ON(direction & ~(READ | WRITE));
1195         *i = (struct iov_iter){
1196                 .iter_type = ITER_BVEC,
1197                 .data_source = direction,
1198                 .bvec = bvec,
1199                 .nr_segs = nr_segs,
1200                 .iov_offset = 0,
1201                 .count = count
1202         };
1203 }
1204 EXPORT_SYMBOL(iov_iter_bvec);
1205
1206 void iov_iter_pipe(struct iov_iter *i, unsigned int direction,
1207                         struct pipe_inode_info *pipe,
1208                         size_t count)
1209 {
1210         BUG_ON(direction != READ);
1211         WARN_ON(pipe_full(pipe->head, pipe->tail, pipe->ring_size));
1212         *i = (struct iov_iter){
1213                 .iter_type = ITER_PIPE,
1214                 .data_source = false,
1215                 .pipe = pipe,
1216                 .head = pipe->head,
1217                 .start_head = pipe->head,
1218                 .iov_offset = 0,
1219                 .count = count
1220         };
1221 }
1222 EXPORT_SYMBOL(iov_iter_pipe);
1223
1224 /**
1225  * iov_iter_xarray - Initialise an I/O iterator to use the pages in an xarray
1226  * @i: The iterator to initialise.
1227  * @direction: The direction of the transfer.
1228  * @xarray: The xarray to access.
1229  * @start: The start file position.
1230  * @count: The size of the I/O buffer in bytes.
1231  *
1232  * Set up an I/O iterator to either draw data out of the pages attached to an
1233  * inode or to inject data into those pages.  The pages *must* be prevented
1234  * from evaporation, either by taking a ref on them or locking them by the
1235  * caller.
1236  */
1237 void iov_iter_xarray(struct iov_iter *i, unsigned int direction,
1238                      struct xarray *xarray, loff_t start, size_t count)
1239 {
1240         BUG_ON(direction & ~1);
1241         *i = (struct iov_iter) {
1242                 .iter_type = ITER_XARRAY,
1243                 .data_source = direction,
1244                 .xarray = xarray,
1245                 .xarray_start = start,
1246                 .count = count,
1247                 .iov_offset = 0
1248         };
1249 }
1250 EXPORT_SYMBOL(iov_iter_xarray);
1251
1252 /**
1253  * iov_iter_discard - Initialise an I/O iterator that discards data
1254  * @i: The iterator to initialise.
1255  * @direction: The direction of the transfer.
1256  * @count: The size of the I/O buffer in bytes.
1257  *
1258  * Set up an I/O iterator that just discards everything that's written to it.
1259  * It's only available as a READ iterator.
1260  */
1261 void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count)
1262 {
1263         BUG_ON(direction != READ);
1264         *i = (struct iov_iter){
1265                 .iter_type = ITER_DISCARD,
1266                 .data_source = false,
1267                 .count = count,
1268                 .iov_offset = 0
1269         };
1270 }
1271 EXPORT_SYMBOL(iov_iter_discard);
1272
1273 static unsigned long iov_iter_alignment_iovec(const struct iov_iter *i)
1274 {
1275         unsigned long res = 0;
1276         size_t size = i->count;
1277         size_t skip = i->iov_offset;
1278         unsigned k;
1279
1280         for (k = 0; k < i->nr_segs; k++, skip = 0) {
1281                 size_t len = i->iov[k].iov_len - skip;
1282                 if (len) {
1283                         res |= (unsigned long)i->iov[k].iov_base + skip;
1284                         if (len > size)
1285                                 len = size;
1286                         res |= len;
1287                         size -= len;
1288                         if (!size)
1289                                 break;
1290                 }
1291         }
1292         return res;
1293 }
1294
1295 static unsigned long iov_iter_alignment_bvec(const struct iov_iter *i)
1296 {
1297         unsigned res = 0;
1298         size_t size = i->count;
1299         unsigned skip = i->iov_offset;
1300         unsigned k;
1301
1302         for (k = 0; k < i->nr_segs; k++, skip = 0) {
1303                 size_t len = i->bvec[k].bv_len - skip;
1304                 res |= (unsigned long)i->bvec[k].bv_offset + skip;
1305                 if (len > size)
1306                         len = size;
1307                 res |= len;
1308                 size -= len;
1309                 if (!size)
1310                         break;
1311         }
1312         return res;
1313 }
1314
1315 unsigned long iov_iter_alignment(const struct iov_iter *i)
1316 {
1317         /* iovec and kvec have identical layouts */
1318         if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
1319                 return iov_iter_alignment_iovec(i);
1320
1321         if (iov_iter_is_bvec(i))
1322                 return iov_iter_alignment_bvec(i);
1323
1324         if (iov_iter_is_pipe(i)) {
1325                 unsigned int p_mask = i->pipe->ring_size - 1;
1326                 size_t size = i->count;
1327
1328                 if (size && i->iov_offset && allocated(&i->pipe->bufs[i->head & p_mask]))
1329                         return size | i->iov_offset;
1330                 return size;
1331         }
1332
1333         if (iov_iter_is_xarray(i))
1334                 return (i->xarray_start + i->iov_offset) | i->count;
1335
1336         return 0;
1337 }
1338 EXPORT_SYMBOL(iov_iter_alignment);
1339
1340 unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
1341 {
1342         unsigned long res = 0;
1343         unsigned long v = 0;
1344         size_t size = i->count;
1345         unsigned k;
1346
1347         if (WARN_ON(!iter_is_iovec(i)))
1348                 return ~0U;
1349
1350         for (k = 0; k < i->nr_segs; k++) {
1351                 if (i->iov[k].iov_len) {
1352                         unsigned long base = (unsigned long)i->iov[k].iov_base;
1353                         if (v) // if not the first one
1354                                 res |= base | v; // this start | previous end
1355                         v = base + i->iov[k].iov_len;
1356                         if (size <= i->iov[k].iov_len)
1357                                 break;
1358                         size -= i->iov[k].iov_len;
1359                 }
1360         }
1361         return res;
1362 }
1363 EXPORT_SYMBOL(iov_iter_gap_alignment);
1364
1365 static inline ssize_t __pipe_get_pages(struct iov_iter *i,
1366                                 size_t maxsize,
1367                                 struct page **pages,
1368                                 int iter_head,
1369                                 size_t *start)
1370 {
1371         struct pipe_inode_info *pipe = i->pipe;
1372         unsigned int p_mask = pipe->ring_size - 1;
1373         ssize_t n = push_pipe(i, maxsize, &iter_head, start);
1374         if (!n)
1375                 return -EFAULT;
1376
1377         maxsize = n;
1378         n += *start;
1379         while (n > 0) {
1380                 get_page(*pages++ = pipe->bufs[iter_head & p_mask].page);
1381                 iter_head++;
1382                 n -= PAGE_SIZE;
1383         }
1384
1385         return maxsize;
1386 }
1387
1388 static ssize_t pipe_get_pages(struct iov_iter *i,
1389                    struct page **pages, size_t maxsize, unsigned maxpages,
1390                    size_t *start)
1391 {
1392         unsigned int iter_head, npages;
1393         size_t capacity;
1394
1395         if (!sanity(i))
1396                 return -EFAULT;
1397
1398         data_start(i, &iter_head, start);
1399         /* Amount of free space: some of this one + all after this one */
1400         npages = pipe_space_for_user(iter_head, i->pipe->tail, i->pipe);
1401         capacity = min(npages, maxpages) * PAGE_SIZE - *start;
1402
1403         return __pipe_get_pages(i, min(maxsize, capacity), pages, iter_head, start);
1404 }
1405
1406 static ssize_t iter_xarray_populate_pages(struct page **pages, struct xarray *xa,
1407                                           pgoff_t index, unsigned int nr_pages)
1408 {
1409         XA_STATE(xas, xa, index);
1410         struct page *page;
1411         unsigned int ret = 0;
1412
1413         rcu_read_lock();
1414         for (page = xas_load(&xas); page; page = xas_next(&xas)) {
1415                 if (xas_retry(&xas, page))
1416                         continue;
1417
1418                 /* Has the page moved or been split? */
1419                 if (unlikely(page != xas_reload(&xas))) {
1420                         xas_reset(&xas);
1421                         continue;
1422                 }
1423
1424                 pages[ret] = find_subpage(page, xas.xa_index);
1425                 get_page(pages[ret]);
1426                 if (++ret == nr_pages)
1427                         break;
1428         }
1429         rcu_read_unlock();
1430         return ret;
1431 }
1432
1433 static ssize_t iter_xarray_get_pages(struct iov_iter *i,
1434                                      struct page **pages, size_t maxsize,
1435                                      unsigned maxpages, size_t *_start_offset)
1436 {
1437         unsigned nr, offset;
1438         pgoff_t index, count;
1439         size_t size = maxsize;
1440         loff_t pos;
1441
1442         if (!size || !maxpages)
1443                 return 0;
1444
1445         pos = i->xarray_start + i->iov_offset;
1446         index = pos >> PAGE_SHIFT;
1447         offset = pos & ~PAGE_MASK;
1448         *_start_offset = offset;
1449
1450         count = 1;
1451         if (size > PAGE_SIZE - offset) {
1452                 size -= PAGE_SIZE - offset;
1453                 count += size >> PAGE_SHIFT;
1454                 size &= ~PAGE_MASK;
1455                 if (size)
1456                         count++;
1457         }
1458
1459         if (count > maxpages)
1460                 count = maxpages;
1461
1462         nr = iter_xarray_populate_pages(pages, i->xarray, index, count);
1463         if (nr == 0)
1464                 return 0;
1465
1466         return min_t(size_t, nr * PAGE_SIZE - offset, maxsize);
1467 }
1468
1469 /* must be done on non-empty ITER_IOVEC one */
1470 static unsigned long first_iovec_segment(const struct iov_iter *i,
1471                                          size_t *size, size_t *start,
1472                                          size_t maxsize, unsigned maxpages)
1473 {
1474         size_t skip;
1475         long k;
1476
1477         for (k = 0, skip = i->iov_offset; k < i->nr_segs; k++, skip = 0) {
1478                 unsigned long addr = (unsigned long)i->iov[k].iov_base + skip;
1479                 size_t len = i->iov[k].iov_len - skip;
1480
1481                 if (unlikely(!len))
1482                         continue;
1483                 if (len > maxsize)
1484                         len = maxsize;
1485                 len += (*start = addr % PAGE_SIZE);
1486                 if (len > maxpages * PAGE_SIZE)
1487                         len = maxpages * PAGE_SIZE;
1488                 *size = len;
1489                 return addr & PAGE_MASK;
1490         }
1491         BUG(); // if it had been empty, we wouldn't get called
1492 }
1493
1494 /* must be done on non-empty ITER_BVEC one */
1495 static struct page *first_bvec_segment(const struct iov_iter *i,
1496                                        size_t *size, size_t *start,
1497                                        size_t maxsize, unsigned maxpages)
1498 {
1499         struct page *page;
1500         size_t skip = i->iov_offset, len;
1501
1502         len = i->bvec->bv_len - skip;
1503         if (len > maxsize)
1504                 len = maxsize;
1505         skip += i->bvec->bv_offset;
1506         page = i->bvec->bv_page + skip / PAGE_SIZE;
1507         len += (*start = skip % PAGE_SIZE);
1508         if (len > maxpages * PAGE_SIZE)
1509                 len = maxpages * PAGE_SIZE;
1510         *size = len;
1511         return page;
1512 }
1513
1514 ssize_t iov_iter_get_pages(struct iov_iter *i,
1515                    struct page **pages, size_t maxsize, unsigned maxpages,
1516                    size_t *start)
1517 {
1518         size_t len;
1519         int n, res;
1520
1521         if (maxsize > i->count)
1522                 maxsize = i->count;
1523         if (!maxsize)
1524                 return 0;
1525
1526         if (likely(iter_is_iovec(i))) {
1527                 unsigned int gup_flags = 0;
1528                 unsigned long addr;
1529
1530                 if (iov_iter_rw(i) != WRITE)
1531                         gup_flags |= FOLL_WRITE;
1532                 if (i->nofault)
1533                         gup_flags |= FOLL_NOFAULT;
1534
1535                 addr = first_iovec_segment(i, &len, start, maxsize, maxpages);
1536                 n = DIV_ROUND_UP(len, PAGE_SIZE);
1537                 res = get_user_pages_fast(addr, n, gup_flags, pages);
1538                 if (unlikely(res <= 0))
1539                         return res;
1540                 return (res == n ? len : res * PAGE_SIZE) - *start;
1541         }
1542         if (iov_iter_is_bvec(i)) {
1543                 struct page *page;
1544
1545                 page = first_bvec_segment(i, &len, start, maxsize, maxpages);
1546                 n = DIV_ROUND_UP(len, PAGE_SIZE);
1547                 while (n--)
1548                         get_page(*pages++ = page++);
1549                 return len - *start;
1550         }
1551         if (iov_iter_is_pipe(i))
1552                 return pipe_get_pages(i, pages, maxsize, maxpages, start);
1553         if (iov_iter_is_xarray(i))
1554                 return iter_xarray_get_pages(i, pages, maxsize, maxpages, start);
1555         return -EFAULT;
1556 }
1557 EXPORT_SYMBOL(iov_iter_get_pages);
1558
1559 static struct page **get_pages_array(size_t n)
1560 {
1561         return kvmalloc_array(n, sizeof(struct page *), GFP_KERNEL);
1562 }
1563
1564 static ssize_t pipe_get_pages_alloc(struct iov_iter *i,
1565                    struct page ***pages, size_t maxsize,
1566                    size_t *start)
1567 {
1568         struct page **p;
1569         unsigned int iter_head, npages;
1570         ssize_t n;
1571
1572         if (!sanity(i))
1573                 return -EFAULT;
1574
1575         data_start(i, &iter_head, start);
1576         /* Amount of free space: some of this one + all after this one */
1577         npages = pipe_space_for_user(iter_head, i->pipe->tail, i->pipe);
1578         n = npages * PAGE_SIZE - *start;
1579         if (maxsize > n)
1580                 maxsize = n;
1581         else
1582                 npages = DIV_ROUND_UP(maxsize + *start, PAGE_SIZE);
1583         p = get_pages_array(npages);
1584         if (!p)
1585                 return -ENOMEM;
1586         n = __pipe_get_pages(i, maxsize, p, iter_head, start);
1587         if (n > 0)
1588                 *pages = p;
1589         else
1590                 kvfree(p);
1591         return n;
1592 }
1593
1594 static ssize_t iter_xarray_get_pages_alloc(struct iov_iter *i,
1595                                            struct page ***pages, size_t maxsize,
1596                                            size_t *_start_offset)
1597 {
1598         struct page **p;
1599         unsigned nr, offset;
1600         pgoff_t index, count;
1601         size_t size = maxsize;
1602         loff_t pos;
1603
1604         if (!size)
1605                 return 0;
1606
1607         pos = i->xarray_start + i->iov_offset;
1608         index = pos >> PAGE_SHIFT;
1609         offset = pos & ~PAGE_MASK;
1610         *_start_offset = offset;
1611
1612         count = 1;
1613         if (size > PAGE_SIZE - offset) {
1614                 size -= PAGE_SIZE - offset;
1615                 count += size >> PAGE_SHIFT;
1616                 size &= ~PAGE_MASK;
1617                 if (size)
1618                         count++;
1619         }
1620
1621         p = get_pages_array(count);
1622         if (!p)
1623                 return -ENOMEM;
1624         *pages = p;
1625
1626         nr = iter_xarray_populate_pages(p, i->xarray, index, count);
1627         if (nr == 0)
1628                 return 0;
1629
1630         return min_t(size_t, nr * PAGE_SIZE - offset, maxsize);
1631 }
1632
1633 ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
1634                    struct page ***pages, size_t maxsize,
1635                    size_t *start)
1636 {
1637         struct page **p;
1638         size_t len;
1639         int n, res;
1640
1641         if (maxsize > i->count)
1642                 maxsize = i->count;
1643         if (!maxsize)
1644                 return 0;
1645
1646         if (likely(iter_is_iovec(i))) {
1647                 unsigned int gup_flags = 0;
1648                 unsigned long addr;
1649
1650                 if (iov_iter_rw(i) != WRITE)
1651                         gup_flags |= FOLL_WRITE;
1652                 if (i->nofault)
1653                         gup_flags |= FOLL_NOFAULT;
1654
1655                 addr = first_iovec_segment(i, &len, start, maxsize, ~0U);
1656                 n = DIV_ROUND_UP(len, PAGE_SIZE);
1657                 p = get_pages_array(n);
1658                 if (!p)
1659                         return -ENOMEM;
1660                 res = get_user_pages_fast(addr, n, gup_flags, p);
1661                 if (unlikely(res <= 0)) {
1662                         kvfree(p);
1663                         *pages = NULL;
1664                         return res;
1665                 }
1666                 *pages = p;
1667                 return (res == n ? len : res * PAGE_SIZE) - *start;
1668         }
1669         if (iov_iter_is_bvec(i)) {
1670                 struct page *page;
1671
1672                 page = first_bvec_segment(i, &len, start, maxsize, ~0U);
1673                 n = DIV_ROUND_UP(len, PAGE_SIZE);
1674                 *pages = p = get_pages_array(n);
1675                 if (!p)
1676                         return -ENOMEM;
1677                 while (n--)
1678                         get_page(*p++ = page++);
1679                 return len - *start;
1680         }
1681         if (iov_iter_is_pipe(i))
1682                 return pipe_get_pages_alloc(i, pages, maxsize, start);
1683         if (iov_iter_is_xarray(i))
1684                 return iter_xarray_get_pages_alloc(i, pages, maxsize, start);
1685         return -EFAULT;
1686 }
1687 EXPORT_SYMBOL(iov_iter_get_pages_alloc);
1688
1689 size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum,
1690                                struct iov_iter *i)
1691 {
1692         __wsum sum, next;
1693         sum = *csum;
1694         if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {
1695                 WARN_ON(1);
1696                 return 0;
1697         }
1698         iterate_and_advance(i, bytes, base, len, off, ({
1699                 next = csum_and_copy_from_user(base, addr + off, len);
1700                 sum = csum_block_add(sum, next, off);
1701                 next ? 0 : len;
1702         }), ({
1703                 sum = csum_and_memcpy(addr + off, base, len, sum, off);
1704         })
1705         )
1706         *csum = sum;
1707         return bytes;
1708 }
1709 EXPORT_SYMBOL(csum_and_copy_from_iter);
1710
1711 size_t csum_and_copy_to_iter(const void *addr, size_t bytes, void *_csstate,
1712                              struct iov_iter *i)
1713 {
1714         struct csum_state *csstate = _csstate;
1715         __wsum sum, next;
1716
1717         if (unlikely(iov_iter_is_discard(i))) {
1718                 WARN_ON(1);     /* for now */
1719                 return 0;
1720         }
1721
1722         sum = csum_shift(csstate->csum, csstate->off);
1723         if (unlikely(iov_iter_is_pipe(i)))
1724                 bytes = csum_and_copy_to_pipe_iter(addr, bytes, i, &sum);
1725         else iterate_and_advance(i, bytes, base, len, off, ({
1726                 next = csum_and_copy_to_user(addr + off, base, len);
1727                 sum = csum_block_add(sum, next, off);
1728                 next ? 0 : len;
1729         }), ({
1730                 sum = csum_and_memcpy(base, addr + off, len, sum, off);
1731         })
1732         )
1733         csstate->csum = csum_shift(sum, csstate->off);
1734         csstate->off += bytes;
1735         return bytes;
1736 }
1737 EXPORT_SYMBOL(csum_and_copy_to_iter);
1738
1739 size_t hash_and_copy_to_iter(const void *addr, size_t bytes, void *hashp,
1740                 struct iov_iter *i)
1741 {
1742 #ifdef CONFIG_CRYPTO_HASH
1743         struct ahash_request *hash = hashp;
1744         struct scatterlist sg;
1745         size_t copied;
1746
1747         copied = copy_to_iter(addr, bytes, i);
1748         sg_init_one(&sg, addr, copied);
1749         ahash_request_set_crypt(hash, &sg, NULL, copied);
1750         crypto_ahash_update(hash);
1751         return copied;
1752 #else
1753         return 0;
1754 #endif
1755 }
1756 EXPORT_SYMBOL(hash_and_copy_to_iter);
1757
1758 static int iov_npages(const struct iov_iter *i, int maxpages)
1759 {
1760         size_t skip = i->iov_offset, size = i->count;
1761         const struct iovec *p;
1762         int npages = 0;
1763
1764         for (p = i->iov; size; skip = 0, p++) {
1765                 unsigned offs = offset_in_page(p->iov_base + skip);
1766                 size_t len = min(p->iov_len - skip, size);
1767
1768                 if (len) {
1769                         size -= len;
1770                         npages += DIV_ROUND_UP(offs + len, PAGE_SIZE);
1771                         if (unlikely(npages > maxpages))
1772                                 return maxpages;
1773                 }
1774         }
1775         return npages;
1776 }
1777
1778 static int bvec_npages(const struct iov_iter *i, int maxpages)
1779 {
1780         size_t skip = i->iov_offset, size = i->count;
1781         const struct bio_vec *p;
1782         int npages = 0;
1783
1784         for (p = i->bvec; size; skip = 0, p++) {
1785                 unsigned offs = (p->bv_offset + skip) % PAGE_SIZE;
1786                 size_t len = min(p->bv_len - skip, size);
1787
1788                 size -= len;
1789                 npages += DIV_ROUND_UP(offs + len, PAGE_SIZE);
1790                 if (unlikely(npages > maxpages))
1791                         return maxpages;
1792         }
1793         return npages;
1794 }
1795
1796 int iov_iter_npages(const struct iov_iter *i, int maxpages)
1797 {
1798         if (unlikely(!i->count))
1799                 return 0;
1800         /* iovec and kvec have identical layouts */
1801         if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
1802                 return iov_npages(i, maxpages);
1803         if (iov_iter_is_bvec(i))
1804                 return bvec_npages(i, maxpages);
1805         if (iov_iter_is_pipe(i)) {
1806                 unsigned int iter_head;
1807                 int npages;
1808                 size_t off;
1809
1810                 if (!sanity(i))
1811                         return 0;
1812
1813                 data_start(i, &iter_head, &off);
1814                 /* some of this one + all after this one */
1815                 npages = pipe_space_for_user(iter_head, i->pipe->tail, i->pipe);
1816                 return min(npages, maxpages);
1817         }
1818         if (iov_iter_is_xarray(i)) {
1819                 unsigned offset = (i->xarray_start + i->iov_offset) % PAGE_SIZE;
1820                 int npages = DIV_ROUND_UP(offset + i->count, PAGE_SIZE);
1821                 return min(npages, maxpages);
1822         }
1823         return 0;
1824 }
1825 EXPORT_SYMBOL(iov_iter_npages);
1826
1827 const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
1828 {
1829         *new = *old;
1830         if (unlikely(iov_iter_is_pipe(new))) {
1831                 WARN_ON(1);
1832                 return NULL;
1833         }
1834         if (unlikely(iov_iter_is_discard(new) || iov_iter_is_xarray(new)))
1835                 return NULL;
1836         if (iov_iter_is_bvec(new))
1837                 return new->bvec = kmemdup(new->bvec,
1838                                     new->nr_segs * sizeof(struct bio_vec),
1839                                     flags);
1840         else
1841                 /* iovec and kvec have identical layout */
1842                 return new->iov = kmemdup(new->iov,
1843                                    new->nr_segs * sizeof(struct iovec),
1844                                    flags);
1845 }
1846 EXPORT_SYMBOL(dup_iter);
1847
1848 static int copy_compat_iovec_from_user(struct iovec *iov,
1849                 const struct iovec __user *uvec, unsigned long nr_segs)
1850 {
1851         const struct compat_iovec __user *uiov =
1852                 (const struct compat_iovec __user *)uvec;
1853         int ret = -EFAULT, i;
1854
1855         if (!user_access_begin(uiov, nr_segs * sizeof(*uiov)))
1856                 return -EFAULT;
1857
1858         for (i = 0; i < nr_segs; i++) {
1859                 compat_uptr_t buf;
1860                 compat_ssize_t len;
1861
1862                 unsafe_get_user(len, &uiov[i].iov_len, uaccess_end);
1863                 unsafe_get_user(buf, &uiov[i].iov_base, uaccess_end);
1864
1865                 /* check for compat_size_t not fitting in compat_ssize_t .. */
1866                 if (len < 0) {
1867                         ret = -EINVAL;
1868                         goto uaccess_end;
1869                 }
1870                 iov[i].iov_base = compat_ptr(buf);
1871                 iov[i].iov_len = len;
1872         }
1873
1874         ret = 0;
1875 uaccess_end:
1876         user_access_end();
1877         return ret;
1878 }
1879
1880 static int copy_iovec_from_user(struct iovec *iov,
1881                 const struct iovec __user *uvec, unsigned long nr_segs)
1882 {
1883         unsigned long seg;
1884
1885         if (copy_from_user(iov, uvec, nr_segs * sizeof(*uvec)))
1886                 return -EFAULT;
1887         for (seg = 0; seg < nr_segs; seg++) {
1888                 if ((ssize_t)iov[seg].iov_len < 0)
1889                         return -EINVAL;
1890         }
1891
1892         return 0;
1893 }
1894
1895 struct iovec *iovec_from_user(const struct iovec __user *uvec,
1896                 unsigned long nr_segs, unsigned long fast_segs,
1897                 struct iovec *fast_iov, bool compat)
1898 {
1899         struct iovec *iov = fast_iov;
1900         int ret;
1901
1902         /*
1903          * SuS says "The readv() function *may* fail if the iovcnt argument was
1904          * less than or equal to 0, or greater than {IOV_MAX}.  Linux has
1905          * traditionally returned zero for zero segments, so...
1906          */
1907         if (nr_segs == 0)
1908                 return iov;
1909         if (nr_segs > UIO_MAXIOV)
1910                 return ERR_PTR(-EINVAL);
1911         if (nr_segs > fast_segs) {
1912                 iov = kmalloc_array(nr_segs, sizeof(struct iovec), GFP_KERNEL);
1913                 if (!iov)
1914                         return ERR_PTR(-ENOMEM);
1915         }
1916
1917         if (compat)
1918                 ret = copy_compat_iovec_from_user(iov, uvec, nr_segs);
1919         else
1920                 ret = copy_iovec_from_user(iov, uvec, nr_segs);
1921         if (ret) {
1922                 if (iov != fast_iov)
1923                         kfree(iov);
1924                 return ERR_PTR(ret);
1925         }
1926
1927         return iov;
1928 }
1929
1930 ssize_t __import_iovec(int type, const struct iovec __user *uvec,
1931                  unsigned nr_segs, unsigned fast_segs, struct iovec **iovp,
1932                  struct iov_iter *i, bool compat)
1933 {
1934         ssize_t total_len = 0;
1935         unsigned long seg;
1936         struct iovec *iov;
1937
1938         iov = iovec_from_user(uvec, nr_segs, fast_segs, *iovp, compat);
1939         if (IS_ERR(iov)) {
1940                 *iovp = NULL;
1941                 return PTR_ERR(iov);
1942         }
1943
1944         /*
1945          * According to the Single Unix Specification we should return EINVAL if
1946          * an element length is < 0 when cast to ssize_t or if the total length
1947          * would overflow the ssize_t return value of the system call.
1948          *
1949          * Linux caps all read/write calls to MAX_RW_COUNT, and avoids the
1950          * overflow case.
1951          */
1952         for (seg = 0; seg < nr_segs; seg++) {
1953                 ssize_t len = (ssize_t)iov[seg].iov_len;
1954
1955                 if (!access_ok(iov[seg].iov_base, len)) {
1956                         if (iov != *iovp)
1957                                 kfree(iov);
1958                         *iovp = NULL;
1959                         return -EFAULT;
1960                 }
1961
1962                 if (len > MAX_RW_COUNT - total_len) {
1963                         len = MAX_RW_COUNT - total_len;
1964                         iov[seg].iov_len = len;
1965                 }
1966                 total_len += len;
1967         }
1968
1969         iov_iter_init(i, type, iov, nr_segs, total_len);
1970         if (iov == *iovp)
1971                 *iovp = NULL;
1972         else
1973                 *iovp = iov;
1974         return total_len;
1975 }
1976
1977 /**
1978  * import_iovec() - Copy an array of &struct iovec from userspace
1979  *     into the kernel, check that it is valid, and initialize a new
1980  *     &struct iov_iter iterator to access it.
1981  *
1982  * @type: One of %READ or %WRITE.
1983  * @uvec: Pointer to the userspace array.
1984  * @nr_segs: Number of elements in userspace array.
1985  * @fast_segs: Number of elements in @iov.
1986  * @iovp: (input and output parameter) Pointer to pointer to (usually small
1987  *     on-stack) kernel array.
1988  * @i: Pointer to iterator that will be initialized on success.
1989  *
1990  * If the array pointed to by *@iov is large enough to hold all @nr_segs,
1991  * then this function places %NULL in *@iov on return. Otherwise, a new
1992  * array will be allocated and the result placed in *@iov. This means that
1993  * the caller may call kfree() on *@iov regardless of whether the small
1994  * on-stack array was used or not (and regardless of whether this function
1995  * returns an error or not).
1996  *
1997  * Return: Negative error code on error, bytes imported on success
1998  */
1999 ssize_t import_iovec(int type, const struct iovec __user *uvec,
2000                  unsigned nr_segs, unsigned fast_segs,
2001                  struct iovec **iovp, struct iov_iter *i)
2002 {
2003         return __import_iovec(type, uvec, nr_segs, fast_segs, iovp, i,
2004                               in_compat_syscall());
2005 }
2006 EXPORT_SYMBOL(import_iovec);
2007
2008 int import_single_range(int rw, void __user *buf, size_t len,
2009                  struct iovec *iov, struct iov_iter *i)
2010 {
2011         if (len > MAX_RW_COUNT)
2012                 len = MAX_RW_COUNT;
2013         if (unlikely(!access_ok(buf, len)))
2014                 return -EFAULT;
2015
2016         iov->iov_base = buf;
2017         iov->iov_len = len;
2018         iov_iter_init(i, rw, iov, 1, len);
2019         return 0;
2020 }
2021 EXPORT_SYMBOL(import_single_range);
2022
2023 /**
2024  * iov_iter_restore() - Restore a &struct iov_iter to the same state as when
2025  *     iov_iter_save_state() was called.
2026  *
2027  * @i: &struct iov_iter to restore
2028  * @state: state to restore from
2029  *
2030  * Used after iov_iter_save_state() to bring restore @i, if operations may
2031  * have advanced it.
2032  *
2033  * Note: only works on ITER_IOVEC, ITER_BVEC, and ITER_KVEC
2034  */
2035 void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state)
2036 {
2037         if (WARN_ON_ONCE(!iov_iter_is_bvec(i) && !iter_is_iovec(i)) &&
2038                          !iov_iter_is_kvec(i))
2039                 return;
2040         i->iov_offset = state->iov_offset;
2041         i->count = state->count;
2042         /*
2043          * For the *vec iters, nr_segs + iov is constant - if we increment
2044          * the vec, then we also decrement the nr_segs count. Hence we don't
2045          * need to track both of these, just one is enough and we can deduct
2046          * the other from that. ITER_KVEC and ITER_IOVEC are the same struct
2047          * size, so we can just increment the iov pointer as they are unionzed.
2048          * ITER_BVEC _may_ be the same size on some archs, but on others it is
2049          * not. Be safe and handle it separately.
2050          */
2051         BUILD_BUG_ON(sizeof(struct iovec) != sizeof(struct kvec));
2052         if (iov_iter_is_bvec(i))
2053                 i->bvec -= state->nr_segs - i->nr_segs;
2054         else
2055                 i->iov -= state->nr_segs - i->nr_segs;
2056         i->nr_segs = state->nr_segs;
2057 }