fs/dax.c

   1 /*
   2  * fs/dax.c - Direct Access filesystem code
   3  * Copyright (c) 2013-2014 Intel Corporation
   4  * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
   5  * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
   6  *
   7  * This program is free software; you can redistribute it and/or modify it
   8  * under the terms and conditions of the GNU General Public License,
   9  * version 2, as published by the Free Software Foundation.
  10  *
  11  * This program is distributed in the hope it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  14  * more details.
  15  */
  16
  17 #include <linux/atomic.h>
  18 #include <linux/blkdev.h>
  19 #include <linux/buffer_head.h>
  20 #include <linux/dax.h>
  21 #include <linux/fs.h>
  22 #include <linux/genhd.h>
  23 #include <linux/highmem.h>
  24 #include <linux/memcontrol.h>
  25 #include <linux/mm.h>
  26 #include <linux/mutex.h>
  27 #include <linux/pagevec.h>
  28 #include <linux/pmem.h>
  29 #include <linux/sched.h>
  30 #include <linux/uio.h>
  31 #include <linux/vmstat.h>
  32 #include <linux/pfn_t.h>
  33 #include <linux/sizes.h>
  34
  35 /*
  36  * We use lowest available bit in exceptional entry for locking, other two
  37  * bits to determine entry type. In total 3 special bits.
  38  */
  39 #define RADIX_DAX_SHIFT (RADIX_TREE_EXCEPTIONAL_SHIFT + 3)
  40 #define RADIX_DAX_PTE (1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 1))
  41 #define RADIX_DAX_PMD (1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 2))
  42 #define RADIX_DAX_TYPE_MASK (RADIX_DAX_PTE | RADIX_DAX_PMD)
  43 #define RADIX_DAX_TYPE(entry) ((unsigned long)entry & RADIX_DAX_TYPE_MASK)
  44 #define RADIX_DAX_SECTOR(entry) (((unsigned long)entry >> RADIX_DAX_SHIFT))
  45 #define RADIX_DAX_ENTRY(sector, pmd) ((void *)((unsigned long)sector << \
  46                 RADIX_DAX_SHIFT | (pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE) | \
  47                 RADIX_TREE_EXCEPTIONAL_ENTRY))
  48
  49 /* We choose 4096 entries - same as per-zone page wait tables */
  50 #define DAX_WAIT_TABLE_BITS 12
  51 #define DAX_WAIT_TABLE_ENTRIES (1 << DAX_WAIT_TABLE_BITS)
  52
  53 wait_queue_head_t wait_table[DAX_WAIT_TABLE_ENTRIES];
  54
  55 static int __init init_dax_wait_table(void)
  56 {
  57         int i;
  58
  59         for (i = 0; i < DAX_WAIT_TABLE_ENTRIES; i++)
  60                 init_waitqueue_head(wait_table + i);
  61         return 0;
  62 }
  63 fs_initcall(init_dax_wait_table);
  64
  65 static wait_queue_head_t *dax_entry_waitqueue(struct address_space *mapping,
  66                                               pgoff_t index)
  67 {
  68         unsigned long hash = hash_long((unsigned long)mapping ^ index,
  69                                        DAX_WAIT_TABLE_BITS);
  70         return wait_table + hash;
  71 }
  72
  73 static long dax_map_atomic(struct block_device *bdev, struct blk_dax_ctl *dax)
  74 {
  75         struct request_queue *q = bdev->bd_queue;
  76         long rc = -EIO;
  77
  78         dax->addr = (void __pmem *) ERR_PTR(-EIO);
  79         if (blk_queue_enter(q, true) != 0)
  80                 return rc;
  81
  82         rc = bdev_direct_access(bdev, dax);
  83         if (rc < 0) {
  84                 dax->addr = (void __pmem *) ERR_PTR(rc);
  85                 blk_queue_exit(q);
  86                 return rc;
  87         }
  88         return rc;
  89 }
  90
  91 static void dax_unmap_atomic(struct block_device *bdev,
  92                 const struct blk_dax_ctl *dax)
  93 {
  94         if (IS_ERR(dax->addr))
  95                 return;
  96         blk_queue_exit(bdev->bd_queue);
  97 }
  98
  99 struct page *read_dax_sector(struct block_device *bdev, sector_t n)
 100 {
 101         struct page *page = alloc_pages(GFP_KERNEL, 0);
 102         struct blk_dax_ctl dax = {
 103                 .size = PAGE_SIZE,
 104                 .sector = n & ~((((int) PAGE_SIZE) / 512) - 1),
 105         };
 106         long rc;
 107
 108         if (!page)
 109                 return ERR_PTR(-ENOMEM);
 110
 111         rc = dax_map_atomic(bdev, &dax);
 112         if (rc < 0)
 113                 return ERR_PTR(rc);
 114         memcpy_from_pmem(page_address(page), dax.addr, PAGE_SIZE);
 115         dax_unmap_atomic(bdev, &dax);
 116         return page;
 117 }
 118
 119 static bool buffer_written(struct buffer_head *bh)
 120 {
 121         return buffer_mapped(bh) && !buffer_unwritten(bh);
 122 }
 123
 124 /*
 125  * When ext4 encounters a hole, it returns without modifying the buffer_head
 126  * which means that we can't trust b_size.  To cope with this, we set b_state
 127  * to 0 before calling get_block and, if any bit is set, we know we can trust
 128  * b_size.  Unfortunate, really, since ext4 knows precisely how long a hole is
 129  * and would save us time calling get_block repeatedly.
 130  */
 131 static bool buffer_size_valid(struct buffer_head *bh)
 132 {
 133         return bh->b_state != 0;
 134 }
 135
 136
 137 static sector_t to_sector(const struct buffer_head *bh,
 138                 const struct inode *inode)
 139 {
 140         sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
 141
 142         return sector;
 143 }
 144
 145 static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
 146                       loff_t start, loff_t end, get_block_t get_block,
 147                       struct buffer_head *bh)
 148 {
 149         loff_t pos = start, max = start, bh_max = start;
 150         bool hole = false, need_wmb = false;
 151         struct block_device *bdev = NULL;
 152         int rw = iov_iter_rw(iter), rc;
 153         long map_len = 0;
 154         struct blk_dax_ctl dax = {
 155                 .addr = (void __pmem *) ERR_PTR(-EIO),
 156         };
 157         unsigned blkbits = inode->i_blkbits;
 158         sector_t file_blks = (i_size_read(inode) + (1 << blkbits) - 1)
 159                                                                 >> blkbits;
 160
 161         if (rw == READ)
 162                 end = min(end, i_size_read(inode));
 163
 164         while (pos < end) {
 165                 size_t len;
 166                 if (pos == max) {
 167                         long page = pos >> PAGE_SHIFT;
 168                         sector_t block = page << (PAGE_SHIFT - blkbits);
 169                         unsigned first = pos - (block << blkbits);
 170                         long size;
 171
 172                         if (pos == bh_max) {
 173                                 bh->b_size = PAGE_ALIGN(end - pos);
 174                                 bh->b_state = 0;
 175                                 rc = get_block(inode, block, bh, rw == WRITE);
 176                                 if (rc)
 177                                         break;
 178                                 if (!buffer_size_valid(bh))
 179                                         bh->b_size = 1 << blkbits;
 180                                 bh_max = pos - first + bh->b_size;
 181                                 bdev = bh->b_bdev;
 182                                 /*
 183                                  * We allow uninitialized buffers for writes
 184                                  * beyond EOF as those cannot race with faults
 185                                  */
 186                                 WARN_ON_ONCE(
 187                                         (buffer_new(bh) && block < file_blks) ||
 188                                         (rw == WRITE && buffer_unwritten(bh)));
 189                         } else {
 190                                 unsigned done = bh->b_size -
 191                                                 (bh_max - (pos - first));
 192                                 bh->b_blocknr += done >> blkbits;
 193                                 bh->b_size -= done;
 194                         }
 195
 196                         hole = rw == READ && !buffer_written(bh);
 197                         if (hole) {
 198                                 size = bh->b_size - first;
 199                         } else {
 200                                 dax_unmap_atomic(bdev, &dax);
 201                                 dax.sector = to_sector(bh, inode);
 202                                 dax.size = bh->b_size;
 203                                 map_len = dax_map_atomic(bdev, &dax);
 204                                 if (map_len < 0) {
 205                                         rc = map_len;
 206                                         break;
 207                                 }
 208                                 dax.addr += first;
 209                                 size = map_len - first;
 210                         }
 211                         max = min(pos + size, end);
 212                 }
 213
 214                 if (iov_iter_rw(iter) == WRITE) {
 215                         len = copy_from_iter_pmem(dax.addr, max - pos, iter);
 216                         need_wmb = true;
 217                 } else if (!hole)
 218                         len = copy_to_iter((void __force *) dax.addr, max - pos,
 219                                         iter);
 220                 else
 221                         len = iov_iter_zero(max - pos, iter);
 222
 223                 if (!len) {
 224                         rc = -EFAULT;
 225                         break;
 226                 }
 227
 228                 pos += len;
 229                 if (!IS_ERR(dax.addr))
 230                         dax.addr += len;
 231         }
 232
 233         if (need_wmb)
 234                 wmb_pmem();
 235         dax_unmap_atomic(bdev, &dax);
 236
 237         return (pos == start) ? rc : pos - start;
 238 }
 239
 240 /**
 241  * dax_do_io - Perform I/O to a DAX file
 242  * @iocb: The control block for this I/O
 243  * @inode: The file which the I/O is directed at
 244  * @iter: The addresses to do I/O from or to
 245  * @pos: The file offset where the I/O starts
 246  * @get_block: The filesystem method used to translate file offsets to blocks
 247  * @end_io: A filesystem callback for I/O completion
 248  * @flags: See below
 249  *
 250  * This function uses the same locking scheme as do_blockdev_direct_IO:
 251  * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
 252  * caller for writes.  For reads, we take and release the i_mutex ourselves.
 253  * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
 254  * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
 255  * is in progress.
 256  */
 257 ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
 258                   struct iov_iter *iter, loff_t pos, get_block_t get_block,
 259                   dio_iodone_t end_io, int flags)
 260 {
 261         struct buffer_head bh;
 262         ssize_t retval = -EINVAL;
 263         loff_t end = pos + iov_iter_count(iter);
 264
 265         memset(&bh, 0, sizeof(bh));
 266         bh.b_bdev = inode->i_sb->s_bdev;
 267
 268         if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
 269                 inode_lock(inode);
 270
 271         /* Protects against truncate */
 272         if (!(flags & DIO_SKIP_DIO_COUNT))
 273                 inode_dio_begin(inode);
 274
 275         retval = dax_io(inode, iter, pos, end, get_block, &bh);
 276
 277         if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
 278                 inode_unlock(inode);
 279
 280         if (end_io) {
 281                 int err;
 282
 283                 err = end_io(iocb, pos, retval, bh.b_private);
 284                 if (err)
 285                         retval = err;
 286         }
 287
 288         if (!(flags & DIO_SKIP_DIO_COUNT))
 289                 inode_dio_end(inode);
 290         return retval;
 291 }
 292 EXPORT_SYMBOL_GPL(dax_do_io);
 293
 294 /*
 295  * DAX radix tree locking
 296  */
 297 struct exceptional_entry_key {
 298         struct address_space *mapping;
 299         unsigned long index;
 300 };
 301
 302 struct wait_exceptional_entry_queue {
 303         wait_queue_t wait;
 304         struct exceptional_entry_key key;
 305 };
 306
 307 static int wake_exceptional_entry_func(wait_queue_t *wait, unsigned int mode,
 308                                        int sync, void *keyp)
 309 {
 310         struct exceptional_entry_key *key = keyp;
 311         struct wait_exceptional_entry_queue *ewait =
 312                 container_of(wait, struct wait_exceptional_entry_queue, wait);
 313
 314         if (key->mapping != ewait->key.mapping ||
 315             key->index != ewait->key.index)
 316                 return 0;
 317         return autoremove_wake_function(wait, mode, sync, NULL);
 318 }
 319
 320 /*
 321  * Check whether the given slot is locked. The function must be called with
 322  * mapping->tree_lock held
 323  */
 324 static inline int slot_locked(struct address_space *mapping, void **slot)
 325 {
 326         unsigned long entry = (unsigned long)
 327                 radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
 328         return entry & RADIX_DAX_ENTRY_LOCK;
 329 }
 330
 331 /*
 332  * Mark the given slot is locked. The function must be called with
 333  * mapping->tree_lock held
 334  */
 335 static inline void *lock_slot(struct address_space *mapping, void **slot)
 336 {
 337         unsigned long entry = (unsigned long)
 338                 radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
 339
 340         entry |= RADIX_DAX_ENTRY_LOCK;
 341         radix_tree_replace_slot(slot, (void *)entry);
 342         return (void *)entry;
 343 }
 344
 345 /*
 346  * Mark the given slot is unlocked. The function must be called with
 347  * mapping->tree_lock held
 348  */
 349 static inline void *unlock_slot(struct address_space *mapping, void **slot)
 350 {
 351         unsigned long entry = (unsigned long)
 352                 radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
 353
 354         entry &= ~(unsigned long)RADIX_DAX_ENTRY_LOCK;
 355         radix_tree_replace_slot(slot, (void *)entry);
 356         return (void *)entry;
 357 }
 358
 359 /*
 360  * Lookup entry in radix tree, wait for it to become unlocked if it is
 361  * exceptional entry and return it. The caller must call
 362  * put_unlocked_mapping_entry() when he decided not to lock the entry or
 363  * put_locked_mapping_entry() when he locked the entry and now wants to
 364  * unlock it.
 365  *
 366  * The function must be called with mapping->tree_lock held.
 367  */
 368 static void *get_unlocked_mapping_entry(struct address_space *mapping,
 369                                         pgoff_t index, void ***slotp)
 370 {
 371         void *ret, **slot;
 372         struct wait_exceptional_entry_queue ewait;
 373         wait_queue_head_t *wq = dax_entry_waitqueue(mapping, index);
 374
 375         init_wait(&ewait.wait);
 376         ewait.wait.func = wake_exceptional_entry_func;
 377         ewait.key.mapping = mapping;
 378         ewait.key.index = index;
 379
 380         for (;;) {
 381                 ret = __radix_tree_lookup(&mapping->page_tree, index, NULL,
 382                                           &slot);
 383                 if (!ret || !radix_tree_exceptional_entry(ret) ||
 384                     !slot_locked(mapping, slot)) {
 385                         if (slotp)
 386                                 *slotp = slot;
 387                         return ret;
 388                 }
 389                 prepare_to_wait_exclusive(wq, &ewait.wait,
 390                                           TASK_UNINTERRUPTIBLE);
 391                 spin_unlock_irq(&mapping->tree_lock);
 392                 schedule();
 393                 finish_wait(wq, &ewait.wait);
 394                 spin_lock_irq(&mapping->tree_lock);
 395         }
 396 }
 397
 398 /*
 399  * Find radix tree entry at given index. If it points to a page, return with
 400  * the page locked. If it points to the exceptional entry, return with the
 401  * radix tree entry locked. If the radix tree doesn't contain given index,
 402  * create empty exceptional entry for the index and return with it locked.
 403  *
 404  * Note: Unlike filemap_fault() we don't honor FAULT_FLAG_RETRY flags. For
 405  * persistent memory the benefit is doubtful. We can add that later if we can
 406  * show it helps.
 407  */
 408 static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index)
 409 {
 410         void *ret, **slot;
 411
 412 restart:
 413         spin_lock_irq(&mapping->tree_lock);
 414         ret = get_unlocked_mapping_entry(mapping, index, &slot);
 415         /* No entry for given index? Make sure radix tree is big enough. */
 416         if (!ret) {
 417                 int err;
 418
 419                 spin_unlock_irq(&mapping->tree_lock);
 420                 err = radix_tree_preload(
 421                                 mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM);
 422                 if (err)
 423                         return ERR_PTR(err);
 424                 ret = (void *)(RADIX_TREE_EXCEPTIONAL_ENTRY |
 425                                RADIX_DAX_ENTRY_LOCK);
 426                 spin_lock_irq(&mapping->tree_lock);
 427                 err = radix_tree_insert(&mapping->page_tree, index, ret);
 428                 radix_tree_preload_end();
 429                 if (err) {
 430                         spin_unlock_irq(&mapping->tree_lock);
 431                         /* Someone already created the entry? */
 432                         if (err == -EEXIST)
 433                                 goto restart;
 434                         return ERR_PTR(err);
 435                 }
 436                 /* Good, we have inserted empty locked entry into the tree. */
 437                 mapping->nrexceptional++;
 438                 spin_unlock_irq(&mapping->tree_lock);
 439                 return ret;
 440         }
 441         /* Normal page in radix tree? */
 442         if (!radix_tree_exceptional_entry(ret)) {
 443                 struct page *page = ret;
 444
 445                 get_page(page);
 446                 spin_unlock_irq(&mapping->tree_lock);
 447                 lock_page(page);
 448                 /* Page got truncated? Retry... */
 449                 if (unlikely(page->mapping != mapping)) {
 450                         unlock_page(page);
 451                         put_page(page);
 452                         goto restart;
 453                 }
 454                 return page;
 455         }
 456         ret = lock_slot(mapping, slot);
 457         spin_unlock_irq(&mapping->tree_lock);
 458         return ret;
 459 }
 460
 461 void dax_wake_mapping_entry_waiter(struct address_space *mapping,
 462                                    pgoff_t index, bool wake_all)
 463 {
 464         wait_queue_head_t *wq = dax_entry_waitqueue(mapping, index);
 465
 466         /*
 467          * Checking for locked entry and prepare_to_wait_exclusive() happens
 468          * under mapping->tree_lock, ditto for entry handling in our callers.
 469          * So at this point all tasks that could have seen our entry locked
 470          * must be in the waitqueue and the following check will see them.
 471          */
 472         if (waitqueue_active(wq)) {
 473                 struct exceptional_entry_key key;
 474
 475                 key.mapping = mapping;
 476                 key.index = index;
 477                 __wake_up(wq, TASK_NORMAL, wake_all ? 0 : 1, &key);
 478         }
 479 }
 480
 481 void dax_unlock_mapping_entry(struct address_space *mapping, pgoff_t index)
 482 {
 483         void *ret, **slot;
 484
 485         spin_lock_irq(&mapping->tree_lock);
 486         ret = __radix_tree_lookup(&mapping->page_tree, index, NULL, &slot);
 487         if (WARN_ON_ONCE(!ret || !radix_tree_exceptional_entry(ret) ||
 488                          !slot_locked(mapping, slot))) {
 489                 spin_unlock_irq(&mapping->tree_lock);
 490                 return;
 491         }
 492         unlock_slot(mapping, slot);
 493         spin_unlock_irq(&mapping->tree_lock);
 494         dax_wake_mapping_entry_waiter(mapping, index, false);
 495 }
 496
 497 static void put_locked_mapping_entry(struct address_space *mapping,
 498                                      pgoff_t index, void *entry)
 499 {
 500         if (!radix_tree_exceptional_entry(entry)) {
 501                 unlock_page(entry);
 502                 put_page(entry);
 503         } else {
 504                 dax_unlock_mapping_entry(mapping, index);
 505         }
 506 }
 507
 508 /*
 509  * Called when we are done with radix tree entry we looked up via
 510  * get_unlocked_mapping_entry() and which we didn't lock in the end.
 511  */
 512 static void put_unlocked_mapping_entry(struct address_space *mapping,
 513                                        pgoff_t index, void *entry)
 514 {
 515         if (!radix_tree_exceptional_entry(entry))
 516                 return;
 517
 518         /* We have to wake up next waiter for the radix tree entry lock */
 519         dax_wake_mapping_entry_waiter(mapping, index, false);
 520 }
 521
 522 /*
 523  * Delete exceptional DAX entry at @index from @mapping. Wait for radix tree
 524  * entry to get unlocked before deleting it.
 525  */
 526 int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
 527 {
 528         void *entry;
 529
 530         spin_lock_irq(&mapping->tree_lock);
 531         entry = get_unlocked_mapping_entry(mapping, index, NULL);
 532         /*
 533          * This gets called from truncate / punch_hole path. As such, the caller
 534          * must hold locks protecting against concurrent modifications of the
 535          * radix tree (usually fs-private i_mmap_sem for writing). Since the
 536          * caller has seen exceptional entry for this index, we better find it
 537          * at that index as well...
 538          */
 539         if (WARN_ON_ONCE(!entry || !radix_tree_exceptional_entry(entry))) {
 540                 spin_unlock_irq(&mapping->tree_lock);
 541                 return 0;
 542         }
 543         radix_tree_delete(&mapping->page_tree, index);
 544         mapping->nrexceptional--;
 545         spin_unlock_irq(&mapping->tree_lock);
 546         dax_wake_mapping_entry_waiter(mapping, index, true);
 547
 548         return 1;
 549 }
 550
 551 /*
 552  * The user has performed a load from a hole in the file.  Allocating
 553  * a new page in the file would cause excessive storage usage for
 554  * workloads with sparse files.  We allocate a page cache page instead.
 555  * We'll kick it out of the page cache if it's ever written to,
 556  * otherwise it will simply fall out of the page cache under memory
 557  * pressure without ever having been dirtied.
 558  */
 559 static int dax_load_hole(struct address_space *mapping, void *entry,
 560                          struct vm_fault *vmf)
 561 {
 562         struct page *page;
 563
 564         /* Hole page already exists? Return it...  */
 565         if (!radix_tree_exceptional_entry(entry)) {
 566                 vmf->page = entry;
 567                 return VM_FAULT_LOCKED;
 568         }
 569
 570         /* This will replace locked radix tree entry with a hole page */
 571         page = find_or_create_page(mapping, vmf->pgoff,
 572                                    vmf->gfp_mask | __GFP_ZERO);
 573         if (!page) {
 574                 put_locked_mapping_entry(mapping, vmf->pgoff, entry);
 575                 return VM_FAULT_OOM;
 576         }
 577         vmf->page = page;
 578         return VM_FAULT_LOCKED;
 579 }
 580
 581 static int copy_user_bh(struct page *to, struct inode *inode,
 582                 struct buffer_head *bh, unsigned long vaddr)
 583 {
 584         struct blk_dax_ctl dax = {
 585                 .sector = to_sector(bh, inode),
 586                 .size = bh->b_size,
 587         };
 588         struct block_device *bdev = bh->b_bdev;
 589         void *vto;
 590
 591         if (dax_map_atomic(bdev, &dax) < 0)
 592                 return PTR_ERR(dax.addr);
 593         vto = kmap_atomic(to);
 594         copy_user_page(vto, (void __force *)dax.addr, vaddr, to);
 595         kunmap_atomic(vto);
 596         dax_unmap_atomic(bdev, &dax);
 597         return 0;
 598 }
 599
 600 #define DAX_PMD_INDEX(page_index) (page_index & (PMD_MASK >> PAGE_SHIFT))
 601
 602 static void *dax_insert_mapping_entry(struct address_space *mapping,
 603                                       struct vm_fault *vmf,
 604                                       void *entry, sector_t sector)
 605 {
 606         struct radix_tree_root *page_tree = &mapping->page_tree;
 607         int error = 0;
 608         bool hole_fill = false;
 609         void *new_entry;
 610         pgoff_t index = vmf->pgoff;
 611
 612         if (vmf->flags & FAULT_FLAG_WRITE)
 613                 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 614
 615         /* Replacing hole page with block mapping? */
 616         if (!radix_tree_exceptional_entry(entry)) {
 617                 hole_fill = true;
 618                 /*
 619                  * Unmap the page now before we remove it from page cache below.
 620                  * The page is locked so it cannot be faulted in again.
 621                  */
 622                 unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
 623                                     PAGE_SIZE, 0);
 624                 error = radix_tree_preload(vmf->gfp_mask & ~__GFP_HIGHMEM);
 625                 if (error)
 626                         return ERR_PTR(error);
 627         }
 628
 629         spin_lock_irq(&mapping->tree_lock);
 630         new_entry = (void *)((unsigned long)RADIX_DAX_ENTRY(sector, false) |
 631                        RADIX_DAX_ENTRY_LOCK);
 632         if (hole_fill) {
 633                 __delete_from_page_cache(entry, NULL);
 634                 /* Drop pagecache reference */
 635                 put_page(entry);
 636                 error = radix_tree_insert(page_tree, index, new_entry);
 637                 if (error) {
 638                         new_entry = ERR_PTR(error);
 639                         goto unlock;
 640                 }
 641                 mapping->nrexceptional++;
 642         } else {
 643                 void **slot;
 644                 void *ret;
 645
 646                 ret = __radix_tree_lookup(page_tree, index, NULL, &slot);
 647                 WARN_ON_ONCE(ret != entry);
 648                 radix_tree_replace_slot(slot, new_entry);
 649         }
 650         if (vmf->flags & FAULT_FLAG_WRITE)
 651                 radix_tree_tag_set(page_tree, index, PAGECACHE_TAG_DIRTY);
 652  unlock:
 653         spin_unlock_irq(&mapping->tree_lock);
 654         if (hole_fill) {
 655                 radix_tree_preload_end();
 656                 /*
 657                  * We don't need hole page anymore, it has been replaced with
 658                  * locked radix tree entry now.
 659                  */
 660                 if (mapping->a_ops->freepage)
 661                         mapping->a_ops->freepage(entry);
 662                 unlock_page(entry);
 663                 put_page(entry);
 664         }
 665         return new_entry;
 666 }
 667
 668 static int dax_writeback_one(struct block_device *bdev,
 669                 struct address_space *mapping, pgoff_t index, void *entry)
 670 {
 671         struct radix_tree_root *page_tree = &mapping->page_tree;
 672         int type = RADIX_DAX_TYPE(entry);
 673         struct radix_tree_node *node;
 674         struct blk_dax_ctl dax;
 675         void **slot;
 676         int ret = 0;
 677
 678         spin_lock_irq(&mapping->tree_lock);
 679         /*
 680          * Regular page slots are stabilized by the page lock even
 681          * without the tree itself locked.  These unlocked entries
 682          * need verification under the tree lock.
 683          */
 684         if (!__radix_tree_lookup(page_tree, index, &node, &slot))
 685                 goto unlock;
 686         if (*slot != entry)
 687                 goto unlock;
 688
 689         /* another fsync thread may have already written back this entry */
 690         if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
 691                 goto unlock;
 692
 693         if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD)) {
 694                 ret = -EIO;
 695                 goto unlock;
 696         }
 697
 698         dax.sector = RADIX_DAX_SECTOR(entry);
 699         dax.size = (type == RADIX_DAX_PMD ? PMD_SIZE : PAGE_SIZE);
 700         spin_unlock_irq(&mapping->tree_lock);
 701
 702         /*
 703          * We cannot hold tree_lock while calling dax_map_atomic() because it
 704          * eventually calls cond_resched().
 705          */
 706         ret = dax_map_atomic(bdev, &dax);
 707         if (ret < 0)
 708                 return ret;
 709
 710         if (WARN_ON_ONCE(ret < dax.size)) {
 711                 ret = -EIO;
 712                 goto unmap;
 713         }
 714
 715         wb_cache_pmem(dax.addr, dax.size);
 716
 717         spin_lock_irq(&mapping->tree_lock);
 718         radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
 719         spin_unlock_irq(&mapping->tree_lock);
 720  unmap:
 721         dax_unmap_atomic(bdev, &dax);
 722         return ret;
 723
 724  unlock:
 725         spin_unlock_irq(&mapping->tree_lock);
 726         return ret;
 727 }
 728
 729 /*
 730  * Flush the mapping to the persistent domain within the byte range of [start,
 731  * end]. This is required by data integrity operations to ensure file data is
 732  * on persistent storage prior to completion of the operation.
 733  */
 734 int dax_writeback_mapping_range(struct address_space *mapping,
 735                 struct block_device *bdev, struct writeback_control *wbc)
 736 {
 737         struct inode *inode = mapping->host;
 738         pgoff_t start_index, end_index, pmd_index;
 739         pgoff_t indices[PAGEVEC_SIZE];
 740         struct pagevec pvec;
 741         bool done = false;
 742         int i, ret = 0;
 743         void *entry;
 744
 745         if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))
 746                 return -EIO;
 747
 748         if (!mapping->nrexceptional || wbc->sync_mode != WB_SYNC_ALL)
 749                 return 0;
 750
 751         start_index = wbc->range_start >> PAGE_SHIFT;
 752         end_index = wbc->range_end >> PAGE_SHIFT;
 753         pmd_index = DAX_PMD_INDEX(start_index);
 754
 755         rcu_read_lock();
 756         entry = radix_tree_lookup(&mapping->page_tree, pmd_index);
 757         rcu_read_unlock();
 758
 759         /* see if the start of our range is covered by a PMD entry */
 760         if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
 761                 start_index = pmd_index;
 762
 763         tag_pages_for_writeback(mapping, start_index, end_index);
 764
 765         pagevec_init(&pvec, 0);
 766         while (!done) {
 767                 pvec.nr = find_get_entries_tag(mapping, start_index,
 768                                 PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
 769                                 pvec.pages, indices);
 770
 771                 if (pvec.nr == 0)
 772                         break;
 773
 774                 for (i = 0; i < pvec.nr; i++) {
 775                         if (indices[i] > end_index) {
 776                                 done = true;
 777                                 break;
 778                         }
 779
 780                         ret = dax_writeback_one(bdev, mapping, indices[i],
 781                                         pvec.pages[i]);
 782                         if (ret < 0)
 783                                 return ret;
 784                 }
 785         }
 786         wmb_pmem();
 787         return 0;
 788 }
 789 EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
 790
 791 static int dax_insert_mapping(struct address_space *mapping,
 792                         struct buffer_head *bh, void **entryp,
 793                         struct vm_area_struct *vma, struct vm_fault *vmf)
 794 {
 795         unsigned long vaddr = (unsigned long)vmf->virtual_address;
 796         struct block_device *bdev = bh->b_bdev;
 797         struct blk_dax_ctl dax = {
 798                 .sector = to_sector(bh, mapping->host),
 799                 .size = bh->b_size,
 800         };
 801         int error;
 802         void *ret;
 803         void *entry = *entryp;
 804
 805         i_mmap_lock_read(mapping);
 806
 807         if (dax_map_atomic(bdev, &dax) < 0) {
 808                 error = PTR_ERR(dax.addr);
 809                 goto out;
 810         }
 811         dax_unmap_atomic(bdev, &dax);
 812
 813         ret = dax_insert_mapping_entry(mapping, vmf, entry, dax.sector);
 814         if (IS_ERR(ret)) {
 815                 error = PTR_ERR(ret);
 816                 goto out;
 817         }
 818         *entryp = ret;
 819
 820         error = vm_insert_mixed(vma, vaddr, dax.pfn);
 821  out:
 822         i_mmap_unlock_read(mapping);
 823         return error;
 824 }
 825
 826 /**
 827  * __dax_fault - handle a page fault on a DAX file
 828  * @vma: The virtual memory area where the fault occurred
 829  * @vmf: The description of the fault
 830  * @get_block: The filesystem method used to translate file offsets to blocks
 831  *
 832  * When a page fault occurs, filesystems may call this helper in their
 833  * fault handler for DAX files. __dax_fault() assumes the caller has done all
 834  * the necessary locking for the page fault to proceed successfully.
 835  */
 836 int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
 837                         get_block_t get_block)
 838 {
 839         struct file *file = vma->vm_file;
 840         struct address_space *mapping = file->f_mapping;
 841         struct inode *inode = mapping->host;
 842         void *entry;
 843         struct buffer_head bh;
 844         unsigned long vaddr = (unsigned long)vmf->virtual_address;
 845         unsigned blkbits = inode->i_blkbits;
 846         sector_t block;
 847         pgoff_t size;
 848         int error;
 849         int major = 0;
 850
 851         /*
 852          * Check whether offset isn't beyond end of file now. Caller is supposed
 853          * to hold locks serializing us with truncate / punch hole so this is
 854          * a reliable test.
 855          */
 856         size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 857         if (vmf->pgoff >= size)
 858                 return VM_FAULT_SIGBUS;
 859
 860         memset(&bh, 0, sizeof(bh));
 861         block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
 862         bh.b_bdev = inode->i_sb->s_bdev;
 863         bh.b_size = PAGE_SIZE;
 864
 865         entry = grab_mapping_entry(mapping, vmf->pgoff);
 866         if (IS_ERR(entry)) {
 867                 error = PTR_ERR(entry);
 868                 goto out;
 869         }
 870
 871         error = get_block(inode, block, &bh, 0);
 872         if (!error && (bh.b_size < PAGE_SIZE))
 873                 error = -EIO;           /* fs corruption? */
 874         if (error)
 875                 goto unlock_entry;
 876
 877         if (vmf->cow_page) {
 878                 struct page *new_page = vmf->cow_page;
 879                 if (buffer_written(&bh))
 880                         error = copy_user_bh(new_page, inode, &bh, vaddr);
 881                 else
 882                         clear_user_highpage(new_page, vaddr);
 883                 if (error)
 884                         goto unlock_entry;
 885                 if (!radix_tree_exceptional_entry(entry)) {
 886                         vmf->page = entry;
 887                         return VM_FAULT_LOCKED;
 888                 }
 889                 vmf->entry = entry;
 890                 return VM_FAULT_DAX_LOCKED;
 891         }
 892
 893         if (!buffer_mapped(&bh)) {
 894                 if (vmf->flags & FAULT_FLAG_WRITE) {
 895                         error = get_block(inode, block, &bh, 1);
 896                         count_vm_event(PGMAJFAULT);
 897                         mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
 898                         major = VM_FAULT_MAJOR;
 899                         if (!error && (bh.b_size < PAGE_SIZE))
 900                                 error = -EIO;
 901                         if (error)
 902                                 goto unlock_entry;
 903                 } else {
 904                         return dax_load_hole(mapping, entry, vmf);
 905                 }
 906         }
 907
 908         /* Filesystem should not return unwritten buffers to us! */
 909         WARN_ON_ONCE(buffer_unwritten(&bh) || buffer_new(&bh));
 910         error = dax_insert_mapping(mapping, &bh, &entry, vma, vmf);
 911  unlock_entry:
 912         put_locked_mapping_entry(mapping, vmf->pgoff, entry);
 913  out:
 914         if (error == -ENOMEM)
 915                 return VM_FAULT_OOM | major;
 916         /* -EBUSY is fine, somebody else faulted on the same PTE */
 917         if ((error < 0) && (error != -EBUSY))
 918                 return VM_FAULT_SIGBUS | major;
 919         return VM_FAULT_NOPAGE | major;
 920 }
 921 EXPORT_SYMBOL(__dax_fault);
 922
 923 /**
 924  * dax_fault - handle a page fault on a DAX file
 925  * @vma: The virtual memory area where the fault occurred
 926  * @vmf: The description of the fault
 927  * @get_block: The filesystem method used to translate file offsets to blocks
 928  *
 929  * When a page fault occurs, filesystems may call this helper in their
 930  * fault handler for DAX files.
 931  */
 932 int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
 933               get_block_t get_block)
 934 {
 935         int result;
 936         struct super_block *sb = file_inode(vma->vm_file)->i_sb;
 937
 938         if (vmf->flags & FAULT_FLAG_WRITE) {
 939                 sb_start_pagefault(sb);
 940                 file_update_time(vma->vm_file);
 941         }
 942         result = __dax_fault(vma, vmf, get_block);
 943         if (vmf->flags & FAULT_FLAG_WRITE)
 944                 sb_end_pagefault(sb);
 945
 946         return result;
 947 }
 948 EXPORT_SYMBOL_GPL(dax_fault);
 949
 950 #if defined(CONFIG_TRANSPARENT_HUGEPAGE)
 951 /*
 952  * The 'colour' (ie low bits) within a PMD of a page offset.  This comes up
 953  * more often than one might expect in the below function.
 954  */
 955 #define PG_PMD_COLOUR   ((PMD_SIZE >> PAGE_SHIFT) - 1)
 956
 957 static void __dax_dbg(struct buffer_head *bh, unsigned long address,
 958                 const char *reason, const char *fn)
 959 {
 960         if (bh) {
 961                 char bname[BDEVNAME_SIZE];
 962                 bdevname(bh->b_bdev, bname);
 963                 pr_debug("%s: %s addr: %lx dev %s state %lx start %lld "
 964                         "length %zd fallback: %s\n", fn, current->comm,
 965                         address, bname, bh->b_state, (u64)bh->b_blocknr,
 966                         bh->b_size, reason);
 967         } else {
 968                 pr_debug("%s: %s addr: %lx fallback: %s\n", fn,
 969                         current->comm, address, reason);
 970         }
 971 }
 972
 973 #define dax_pmd_dbg(bh, address, reason)        __dax_dbg(bh, address, reason, "dax_pmd")
 974
 975 int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 976                 pmd_t *pmd, unsigned int flags, get_block_t get_block)
 977 {
 978         struct file *file = vma->vm_file;
 979         struct address_space *mapping = file->f_mapping;
 980         struct inode *inode = mapping->host;
 981         struct buffer_head bh;
 982         unsigned blkbits = inode->i_blkbits;
 983         unsigned long pmd_addr = address & PMD_MASK;
 984         bool write = flags & FAULT_FLAG_WRITE;
 985         struct block_device *bdev;
 986         pgoff_t size, pgoff;
 987         sector_t block;
 988         int result = 0;
 989         bool alloc = false;
 990
 991         /* dax pmd mappings require pfn_t_devmap() */
 992         if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
 993                 return VM_FAULT_FALLBACK;
 994
 995         /* Fall back to PTEs if we're going to COW */
 996         if (write && !(vma->vm_flags & VM_SHARED)) {
 997                 split_huge_pmd(vma, pmd, address);
 998                 dax_pmd_dbg(NULL, address, "cow write");
 999                 return VM_FAULT_FALLBACK;
1000         }
1001         /* If the PMD would extend outside the VMA */
1002         if (pmd_addr < vma->vm_start) {
1003                 dax_pmd_dbg(NULL, address, "vma start unaligned");
1004                 return VM_FAULT_FALLBACK;
1005         }
1006         if ((pmd_addr + PMD_SIZE) > vma->vm_end) {
1007                 dax_pmd_dbg(NULL, address, "vma end unaligned");
1008                 return VM_FAULT_FALLBACK;
1009         }
1010
1011         pgoff = linear_page_index(vma, pmd_addr);
1012         size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
1013         if (pgoff >= size)
1014                 return VM_FAULT_SIGBUS;
1015         /* If the PMD would cover blocks out of the file */
1016         if ((pgoff | PG_PMD_COLOUR) >= size) {
1017                 dax_pmd_dbg(NULL, address,
1018                                 "offset + huge page size > file size");
1019                 return VM_FAULT_FALLBACK;
1020         }
1021
1022         memset(&bh, 0, sizeof(bh));
1023         bh.b_bdev = inode->i_sb->s_bdev;
1024         block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);
1025
1026         bh.b_size = PMD_SIZE;
1027
1028         if (get_block(inode, block, &bh, 0) != 0)
1029                 return VM_FAULT_SIGBUS;
1030
1031         if (!buffer_mapped(&bh) && write) {
1032                 if (get_block(inode, block, &bh, 1) != 0)
1033                         return VM_FAULT_SIGBUS;
1034                 alloc = true;
1035                 WARN_ON_ONCE(buffer_unwritten(&bh) || buffer_new(&bh));
1036         }
1037
1038         bdev = bh.b_bdev;
1039
1040         /*
1041          * If the filesystem isn't willing to tell us the length of a hole,
1042          * just fall back to PTEs.  Calling get_block 512 times in a loop
1043          * would be silly.
1044          */
1045         if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE) {
1046                 dax_pmd_dbg(&bh, address, "allocated block too small");
1047                 return VM_FAULT_FALLBACK;
1048         }
1049
1050         /*
1051          * If we allocated new storage, make sure no process has any
1052          * zero pages covering this hole
1053          */
1054         if (alloc) {
1055                 loff_t lstart = pgoff << PAGE_SHIFT;
1056                 loff_t lend = lstart + PMD_SIZE - 1; /* inclusive */
1057
1058                 truncate_pagecache_range(inode, lstart, lend);
1059         }
1060
1061         i_mmap_lock_read(mapping);
1062
1063         if (!write && !buffer_mapped(&bh)) {
1064                 spinlock_t *ptl;
1065                 pmd_t entry;
1066                 struct page *zero_page = get_huge_zero_page();
1067
1068                 if (unlikely(!zero_page)) {
1069                         dax_pmd_dbg(&bh, address, "no zero page");
1070                         goto fallback;
1071                 }
1072
1073                 ptl = pmd_lock(vma->vm_mm, pmd);
1074                 if (!pmd_none(*pmd)) {
1075                         spin_unlock(ptl);
1076                         dax_pmd_dbg(&bh, address, "pmd already present");
1077                         goto fallback;
1078                 }
1079
1080                 dev_dbg(part_to_dev(bdev->bd_part),
1081                                 "%s: %s addr: %lx pfn: <zero> sect: %llx\n",
1082                                 __func__, current->comm, address,
1083                                 (unsigned long long) to_sector(&bh, inode));
1084
1085                 entry = mk_pmd(zero_page, vma->vm_page_prot);
1086                 entry = pmd_mkhuge(entry);
1087                 set_pmd_at(vma->vm_mm, pmd_addr, pmd, entry);
1088                 result = VM_FAULT_NOPAGE;
1089                 spin_unlock(ptl);
1090         } else {
1091                 struct blk_dax_ctl dax = {
1092                         .sector = to_sector(&bh, inode),
1093                         .size = PMD_SIZE,
1094                 };
1095                 long length = dax_map_atomic(bdev, &dax);
1096
1097                 if (length < 0) {
1098                         dax_pmd_dbg(&bh, address, "dax-error fallback");
1099                         goto fallback;
1100                 }
1101                 if (length < PMD_SIZE) {
1102                         dax_pmd_dbg(&bh, address, "dax-length too small");
1103                         dax_unmap_atomic(bdev, &dax);
1104                         goto fallback;
1105                 }
1106                 if (pfn_t_to_pfn(dax.pfn) & PG_PMD_COLOUR) {
1107                         dax_pmd_dbg(&bh, address, "pfn unaligned");
1108                         dax_unmap_atomic(bdev, &dax);
1109                         goto fallback;
1110                 }
1111
1112                 if (!pfn_t_devmap(dax.pfn)) {
1113                         dax_unmap_atomic(bdev, &dax);
1114                         dax_pmd_dbg(&bh, address, "pfn not in memmap");
1115                         goto fallback;
1116                 }
1117                 dax_unmap_atomic(bdev, &dax);
1118
1119                 /*
1120                  * For PTE faults we insert a radix tree entry for reads, and
1121                  * leave it clean.  Then on the first write we dirty the radix
1122                  * tree entry via the dax_pfn_mkwrite() path.  This sequence
1123                  * allows the dax_pfn_mkwrite() call to be simpler and avoid a
1124                  * call into get_block() to translate the pgoff to a sector in
1125                  * order to be able to create a new radix tree entry.
1126                  *
1127                  * The PMD path doesn't have an equivalent to
1128                  * dax_pfn_mkwrite(), though, so for a read followed by a
1129                  * write we traverse all the way through __dax_pmd_fault()
1130                  * twice.  This means we can just skip inserting a radix tree
1131                  * entry completely on the initial read and just wait until
1132                  * the write to insert a dirty entry.
1133                  */
1134                 if (write) {
1135                         /*
1136                          * We should insert radix-tree entry and dirty it here.
1137                          * For now this is broken...
1138                          */
1139                 }
1140
1141                 dev_dbg(part_to_dev(bdev->bd_part),
1142                                 "%s: %s addr: %lx pfn: %lx sect: %llx\n",
1143                                 __func__, current->comm, address,
1144                                 pfn_t_to_pfn(dax.pfn),
1145                                 (unsigned long long) dax.sector);
1146                 result |= vmf_insert_pfn_pmd(vma, address, pmd,
1147                                 dax.pfn, write);
1148         }
1149
1150  out:
1151         i_mmap_unlock_read(mapping);
1152
1153         return result;
1154
1155  fallback:
1156         count_vm_event(THP_FAULT_FALLBACK);
1157         result = VM_FAULT_FALLBACK;
1158         goto out;
1159 }
1160 EXPORT_SYMBOL_GPL(__dax_pmd_fault);
1161
1162 /**
1163  * dax_pmd_fault - handle a PMD fault on a DAX file
1164  * @vma: The virtual memory area where the fault occurred
1165  * @vmf: The description of the fault
1166  * @get_block: The filesystem method used to translate file offsets to blocks
1167  *
1168  * When a page fault occurs, filesystems may call this helper in their
1169  * pmd_fault handler for DAX files.
1170  */
1171 int dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
1172                         pmd_t *pmd, unsigned int flags, get_block_t get_block)
1173 {
1174         int result;
1175         struct super_block *sb = file_inode(vma->vm_file)->i_sb;
1176
1177         if (flags & FAULT_FLAG_WRITE) {
1178                 sb_start_pagefault(sb);
1179                 file_update_time(vma->vm_file);
1180         }
1181         result = __dax_pmd_fault(vma, address, pmd, flags, get_block);
1182         if (flags & FAULT_FLAG_WRITE)
1183                 sb_end_pagefault(sb);
1184
1185         return result;
1186 }
1187 EXPORT_SYMBOL_GPL(dax_pmd_fault);
1188 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
1189
1190 /**
1191  * dax_pfn_mkwrite - handle first write to DAX page
1192  * @vma: The virtual memory area where the fault occurred
1193  * @vmf: The description of the fault
1194  */
1195 int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
1196 {
1197         struct file *file = vma->vm_file;
1198         struct address_space *mapping = file->f_mapping;
1199         void *entry;
1200         pgoff_t index = vmf->pgoff;
1201
1202         spin_lock_irq(&mapping->tree_lock);
1203         entry = get_unlocked_mapping_entry(mapping, index, NULL);
1204         if (!entry || !radix_tree_exceptional_entry(entry))
1205                 goto out;
1206         radix_tree_tag_set(&mapping->page_tree, index, PAGECACHE_TAG_DIRTY);
1207         put_unlocked_mapping_entry(mapping, index, entry);
1208 out:
1209         spin_unlock_irq(&mapping->tree_lock);
1210         return VM_FAULT_NOPAGE;
1211 }
1212 EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
1213
1214 static bool dax_range_is_aligned(struct block_device *bdev,
1215                                  unsigned int offset, unsigned int length)
1216 {
1217         unsigned short sector_size = bdev_logical_block_size(bdev);
1218
1219         if (!IS_ALIGNED(offset, sector_size))
1220                 return false;
1221         if (!IS_ALIGNED(length, sector_size))
1222                 return false;
1223
1224         return true;
1225 }
1226
1227 int __dax_zero_page_range(struct block_device *bdev, sector_t sector,
1228                 unsigned int offset, unsigned int length)
1229 {
1230         struct blk_dax_ctl dax = {
1231                 .sector         = sector,
1232                 .size           = PAGE_SIZE,
1233         };
1234
1235         if (dax_range_is_aligned(bdev, offset, length)) {
1236                 sector_t start_sector = dax.sector + (offset >> 9);
1237
1238                 return blkdev_issue_zeroout(bdev, start_sector,
1239                                 length >> 9, GFP_NOFS, true);
1240         } else {
1241                 if (dax_map_atomic(bdev, &dax) < 0)
1242                         return PTR_ERR(dax.addr);
1243                 clear_pmem(dax.addr + offset, length);
1244                 wmb_pmem();
1245                 dax_unmap_atomic(bdev, &dax);
1246         }
1247         return 0;
1248 }
1249 EXPORT_SYMBOL_GPL(__dax_zero_page_range);
1250
1251 /**
1252  * dax_zero_page_range - zero a range within a page of a DAX file
1253  * @inode: The file being truncated
1254  * @from: The file offset that is being truncated to
1255  * @length: The number of bytes to zero
1256  * @get_block: The filesystem method used to translate file offsets to blocks
1257  *
1258  * This function can be called by a filesystem when it is zeroing part of a
1259  * page in a DAX file.  This is intended for hole-punch operations.  If
1260  * you are truncating a file, the helper function dax_truncate_page() may be
1261  * more convenient.
1262  */
1263 int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
1264                                                         get_block_t get_block)
1265 {
1266         struct buffer_head bh;
1267         pgoff_t index = from >> PAGE_SHIFT;
1268         unsigned offset = from & (PAGE_SIZE-1);
1269         int err;
1270
1271         /* Block boundary? Nothing to do */
1272         if (!length)
1273                 return 0;
1274         BUG_ON((offset + length) > PAGE_SIZE);
1275
1276         memset(&bh, 0, sizeof(bh));
1277         bh.b_bdev = inode->i_sb->s_bdev;
1278         bh.b_size = PAGE_SIZE;
1279         err = get_block(inode, index, &bh, 0);
1280         if (err < 0 || !buffer_written(&bh))
1281                 return err;
1282
1283         return __dax_zero_page_range(bh.b_bdev, to_sector(&bh, inode),
1284                         offset, length);
1285 }
1286 EXPORT_SYMBOL_GPL(dax_zero_page_range);
1287
1288 /**
1289  * dax_truncate_page - handle a partial page being truncated in a DAX file
1290  * @inode: The file being truncated
1291  * @from: The file offset that is being truncated to
1292  * @get_block: The filesystem method used to translate file offsets to blocks
1293  *
1294  * Similar to block_truncate_page(), this function can be called by a
1295  * filesystem when it is truncating a DAX file to handle the partial page.
1296  */
1297 int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
1298 {
1299         unsigned length = PAGE_ALIGN(from) - from;
1300         return dax_zero_page_range(inode, from, length, get_block);
1301 }
1302 EXPORT_SYMBOL_GPL(dax_truncate_page);