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