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Linux/fs/dax.c

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  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 static long dax_map_atomic(struct block_device *bdev, struct blk_dax_ctl *dax)
 36 {
 37         struct request_queue *q = bdev->bd_queue;
 38         long rc = -EIO;
 39 
 40         dax->addr = (void __pmem *) ERR_PTR(-EIO);
 41         if (blk_queue_enter(q, true) != 0)
 42                 return rc;
 43 
 44         rc = bdev_direct_access(bdev, dax);
 45         if (rc < 0) {
 46                 dax->addr = (void __pmem *) ERR_PTR(rc);
 47                 blk_queue_exit(q);
 48                 return rc;
 49         }
 50         return rc;
 51 }
 52 
 53 static void dax_unmap_atomic(struct block_device *bdev,
 54                 const struct blk_dax_ctl *dax)
 55 {
 56         if (IS_ERR(dax->addr))
 57                 return;
 58         blk_queue_exit(bdev->bd_queue);
 59 }
 60 
 61 struct page *read_dax_sector(struct block_device *bdev, sector_t n)
 62 {
 63         struct page *page = alloc_pages(GFP_KERNEL, 0);
 64         struct blk_dax_ctl dax = {
 65                 .size = PAGE_SIZE,
 66                 .sector = n & ~((((int) PAGE_SIZE) / 512) - 1),
 67         };
 68         long rc;
 69 
 70         if (!page)
 71                 return ERR_PTR(-ENOMEM);
 72 
 73         rc = dax_map_atomic(bdev, &dax);
 74         if (rc < 0)
 75                 return ERR_PTR(rc);
 76         memcpy_from_pmem(page_address(page), dax.addr, PAGE_SIZE);
 77         dax_unmap_atomic(bdev, &dax);
 78         return page;
 79 }
 80 
 81 /*
 82  * dax_clear_sectors() is called from within transaction context from XFS,
 83  * and hence this means the stack from this point must follow GFP_NOFS
 84  * semantics for all operations.
 85  */
 86 int dax_clear_sectors(struct block_device *bdev, sector_t _sector, long _size)
 87 {
 88         struct blk_dax_ctl dax = {
 89                 .sector = _sector,
 90                 .size = _size,
 91         };
 92 
 93         might_sleep();
 94         do {
 95                 long count, sz;
 96 
 97                 count = dax_map_atomic(bdev, &dax);
 98                 if (count < 0)
 99                         return count;
100                 sz = min_t(long, count, SZ_128K);
101                 clear_pmem(dax.addr, sz);
102                 dax.size -= sz;
103                 dax.sector += sz / 512;
104                 dax_unmap_atomic(bdev, &dax);
105                 cond_resched();
106         } while (dax.size);
107 
108         wmb_pmem();
109         return 0;
110 }
111 EXPORT_SYMBOL_GPL(dax_clear_sectors);
112 
113 /* the clear_pmem() calls are ordered by a wmb_pmem() in the caller */
114 static void dax_new_buf(void __pmem *addr, unsigned size, unsigned first,
115                 loff_t pos, loff_t end)
116 {
117         loff_t final = end - pos + first; /* The final byte of the buffer */
118 
119         if (first > 0)
120                 clear_pmem(addr, first);
121         if (final < size)
122                 clear_pmem(addr + final, size - final);
123 }
124 
125 static bool buffer_written(struct buffer_head *bh)
126 {
127         return buffer_mapped(bh) && !buffer_unwritten(bh);
128 }
129 
130 /*
131  * When ext4 encounters a hole, it returns without modifying the buffer_head
132  * which means that we can't trust b_size.  To cope with this, we set b_state
133  * to 0 before calling get_block and, if any bit is set, we know we can trust
134  * b_size.  Unfortunate, really, since ext4 knows precisely how long a hole is
135  * and would save us time calling get_block repeatedly.
136  */
137 static bool buffer_size_valid(struct buffer_head *bh)
138 {
139         return bh->b_state != 0;
140 }
141 
142 
143 static sector_t to_sector(const struct buffer_head *bh,
144                 const struct inode *inode)
145 {
146         sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
147 
148         return sector;
149 }
150 
151 static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
152                       loff_t start, loff_t end, get_block_t get_block,
153                       struct buffer_head *bh)
154 {
155         loff_t pos = start, max = start, bh_max = start;
156         bool hole = false, need_wmb = false;
157         struct block_device *bdev = NULL;
158         int rw = iov_iter_rw(iter), rc;
159         long map_len = 0;
160         struct blk_dax_ctl dax = {
161                 .addr = (void __pmem *) ERR_PTR(-EIO),
162         };
163 
164         if (rw == READ)
165                 end = min(end, i_size_read(inode));
166 
167         while (pos < end) {
168                 size_t len;
169                 if (pos == max) {
170                         unsigned blkbits = inode->i_blkbits;
171                         long page = pos >> PAGE_SHIFT;
172                         sector_t block = page << (PAGE_SHIFT - blkbits);
173                         unsigned first = pos - (block << blkbits);
174                         long size;
175 
176                         if (pos == bh_max) {
177                                 bh->b_size = PAGE_ALIGN(end - pos);
178                                 bh->b_state = 0;
179                                 rc = get_block(inode, block, bh, rw == WRITE);
180                                 if (rc)
181                                         break;
182                                 if (!buffer_size_valid(bh))
183                                         bh->b_size = 1 << blkbits;
184                                 bh_max = pos - first + bh->b_size;
185                                 bdev = bh->b_bdev;
186                         } else {
187                                 unsigned done = bh->b_size -
188                                                 (bh_max - (pos - first));
189                                 bh->b_blocknr += done >> blkbits;
190                                 bh->b_size -= done;
191                         }
192 
193                         hole = rw == READ && !buffer_written(bh);
194                         if (hole) {
195                                 size = bh->b_size - first;
196                         } else {
197                                 dax_unmap_atomic(bdev, &dax);
198                                 dax.sector = to_sector(bh, inode);
199                                 dax.size = bh->b_size;
200                                 map_len = dax_map_atomic(bdev, &dax);
201                                 if (map_len < 0) {
202                                         rc = map_len;
203                                         break;
204                                 }
205                                 if (buffer_unwritten(bh) || buffer_new(bh)) {
206                                         dax_new_buf(dax.addr, map_len, first,
207                                                         pos, end);
208                                         need_wmb = true;
209                                 }
210                                 dax.addr += first;
211                                 size = map_len - first;
212                         }
213                         max = min(pos + size, end);
214                 }
215 
216                 if (iov_iter_rw(iter) == WRITE) {
217                         len = copy_from_iter_pmem(dax.addr, max - pos, iter);
218                         need_wmb = true;
219                 } else if (!hole)
220                         len = copy_to_iter((void __force *) dax.addr, max - pos,
221                                         iter);
222                 else
223                         len = iov_iter_zero(max - pos, iter);
224 
225                 if (!len) {
226                         rc = -EFAULT;
227                         break;
228                 }
229 
230                 pos += len;
231                 if (!IS_ERR(dax.addr))
232                         dax.addr += len;
233         }
234 
235         if (need_wmb)
236                 wmb_pmem();
237         dax_unmap_atomic(bdev, &dax);
238 
239         return (pos == start) ? rc : pos - start;
240 }
241 
242 /**
243  * dax_do_io - Perform I/O to a DAX file
244  * @iocb: The control block for this I/O
245  * @inode: The file which the I/O is directed at
246  * @iter: The addresses to do I/O from or to
247  * @pos: The file offset where the I/O starts
248  * @get_block: The filesystem method used to translate file offsets to blocks
249  * @end_io: A filesystem callback for I/O completion
250  * @flags: See below
251  *
252  * This function uses the same locking scheme as do_blockdev_direct_IO:
253  * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
254  * caller for writes.  For reads, we take and release the i_mutex ourselves.
255  * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
256  * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
257  * is in progress.
258  */
259 ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
260                   struct iov_iter *iter, loff_t pos, get_block_t get_block,
261                   dio_iodone_t end_io, int flags)
262 {
263         struct buffer_head bh;
264         ssize_t retval = -EINVAL;
265         loff_t end = pos + iov_iter_count(iter);
266 
267         memset(&bh, 0, sizeof(bh));
268         bh.b_bdev = inode->i_sb->s_bdev;
269 
270         if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ) {
271                 struct address_space *mapping = inode->i_mapping;
272                 inode_lock(inode);
273                 retval = filemap_write_and_wait_range(mapping, pos, end - 1);
274                 if (retval) {
275                         inode_unlock(inode);
276                         goto out;
277                 }
278         }
279 
280         /* Protects against truncate */
281         if (!(flags & DIO_SKIP_DIO_COUNT))
282                 inode_dio_begin(inode);
283 
284         retval = dax_io(inode, iter, pos, end, get_block, &bh);
285 
286         if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
287                 inode_unlock(inode);
288 
289         if (end_io) {
290                 int err;
291 
292                 err = end_io(iocb, pos, retval, bh.b_private);
293                 if (err)
294                         retval = err;
295         }
296 
297         if (!(flags & DIO_SKIP_DIO_COUNT))
298                 inode_dio_end(inode);
299  out:
300         return retval;
301 }
302 EXPORT_SYMBOL_GPL(dax_do_io);
303 
304 /*
305  * The user has performed a load from a hole in the file.  Allocating
306  * a new page in the file would cause excessive storage usage for
307  * workloads with sparse files.  We allocate a page cache page instead.
308  * We'll kick it out of the page cache if it's ever written to,
309  * otherwise it will simply fall out of the page cache under memory
310  * pressure without ever having been dirtied.
311  */
312 static int dax_load_hole(struct address_space *mapping, struct page *page,
313                                                         struct vm_fault *vmf)
314 {
315         unsigned long size;
316         struct inode *inode = mapping->host;
317         if (!page)
318                 page = find_or_create_page(mapping, vmf->pgoff,
319                                                 GFP_KERNEL | __GFP_ZERO);
320         if (!page)
321                 return VM_FAULT_OOM;
322         /* Recheck i_size under page lock to avoid truncate race */
323         size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
324         if (vmf->pgoff >= size) {
325                 unlock_page(page);
326                 put_page(page);
327                 return VM_FAULT_SIGBUS;
328         }
329 
330         vmf->page = page;
331         return VM_FAULT_LOCKED;
332 }
333 
334 static int copy_user_bh(struct page *to, struct inode *inode,
335                 struct buffer_head *bh, unsigned long vaddr)
336 {
337         struct blk_dax_ctl dax = {
338                 .sector = to_sector(bh, inode),
339                 .size = bh->b_size,
340         };
341         struct block_device *bdev = bh->b_bdev;
342         void *vto;
343 
344         if (dax_map_atomic(bdev, &dax) < 0)
345                 return PTR_ERR(dax.addr);
346         vto = kmap_atomic(to);
347         copy_user_page(vto, (void __force *)dax.addr, vaddr, to);
348         kunmap_atomic(vto);
349         dax_unmap_atomic(bdev, &dax);
350         return 0;
351 }
352 
353 #define NO_SECTOR -1
354 #define DAX_PMD_INDEX(page_index) (page_index & (PMD_MASK >> PAGE_SHIFT))
355 
356 static int dax_radix_entry(struct address_space *mapping, pgoff_t index,
357                 sector_t sector, bool pmd_entry, bool dirty)
358 {
359         struct radix_tree_root *page_tree = &mapping->page_tree;
360         pgoff_t pmd_index = DAX_PMD_INDEX(index);
361         int type, error = 0;
362         void *entry;
363 
364         WARN_ON_ONCE(pmd_entry && !dirty);
365         if (dirty)
366                 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
367 
368         spin_lock_irq(&mapping->tree_lock);
369 
370         entry = radix_tree_lookup(page_tree, pmd_index);
371         if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD) {
372                 index = pmd_index;
373                 goto dirty;
374         }
375 
376         entry = radix_tree_lookup(page_tree, index);
377         if (entry) {
378                 type = RADIX_DAX_TYPE(entry);
379                 if (WARN_ON_ONCE(type != RADIX_DAX_PTE &&
380                                         type != RADIX_DAX_PMD)) {
381                         error = -EIO;
382                         goto unlock;
383                 }
384 
385                 if (!pmd_entry || type == RADIX_DAX_PMD)
386                         goto dirty;
387 
388                 /*
389                  * We only insert dirty PMD entries into the radix tree.  This
390                  * means we don't need to worry about removing a dirty PTE
391                  * entry and inserting a clean PMD entry, thus reducing the
392                  * range we would flush with a follow-up fsync/msync call.
393                  */
394                 radix_tree_delete(&mapping->page_tree, index);
395                 mapping->nrexceptional--;
396         }
397 
398         if (sector == NO_SECTOR) {
399                 /*
400                  * This can happen during correct operation if our pfn_mkwrite
401                  * fault raced against a hole punch operation.  If this
402                  * happens the pte that was hole punched will have been
403                  * unmapped and the radix tree entry will have been removed by
404                  * the time we are called, but the call will still happen.  We
405                  * will return all the way up to wp_pfn_shared(), where the
406                  * pte_same() check will fail, eventually causing page fault
407                  * to be retried by the CPU.
408                  */
409                 goto unlock;
410         }
411 
412         error = radix_tree_insert(page_tree, index,
413                         RADIX_DAX_ENTRY(sector, pmd_entry));
414         if (error)
415                 goto unlock;
416 
417         mapping->nrexceptional++;
418  dirty:
419         if (dirty)
420                 radix_tree_tag_set(page_tree, index, PAGECACHE_TAG_DIRTY);
421  unlock:
422         spin_unlock_irq(&mapping->tree_lock);
423         return error;
424 }
425 
426 static int dax_writeback_one(struct block_device *bdev,
427                 struct address_space *mapping, pgoff_t index, void *entry)
428 {
429         struct radix_tree_root *page_tree = &mapping->page_tree;
430         int type = RADIX_DAX_TYPE(entry);
431         struct radix_tree_node *node;
432         struct blk_dax_ctl dax;
433         void **slot;
434         int ret = 0;
435 
436         spin_lock_irq(&mapping->tree_lock);
437         /*
438          * Regular page slots are stabilized by the page lock even
439          * without the tree itself locked.  These unlocked entries
440          * need verification under the tree lock.
441          */
442         if (!__radix_tree_lookup(page_tree, index, &node, &slot))
443                 goto unlock;
444         if (*slot != entry)
445                 goto unlock;
446 
447         /* another fsync thread may have already written back this entry */
448         if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
449                 goto unlock;
450 
451         if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD)) {
452                 ret = -EIO;
453                 goto unlock;
454         }
455 
456         dax.sector = RADIX_DAX_SECTOR(entry);
457         dax.size = (type == RADIX_DAX_PMD ? PMD_SIZE : PAGE_SIZE);
458         spin_unlock_irq(&mapping->tree_lock);
459 
460         /*
461          * We cannot hold tree_lock while calling dax_map_atomic() because it
462          * eventually calls cond_resched().
463          */
464         ret = dax_map_atomic(bdev, &dax);
465         if (ret < 0)
466                 return ret;
467 
468         if (WARN_ON_ONCE(ret < dax.size)) {
469                 ret = -EIO;
470                 goto unmap;
471         }
472 
473         wb_cache_pmem(dax.addr, dax.size);
474 
475         spin_lock_irq(&mapping->tree_lock);
476         radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
477         spin_unlock_irq(&mapping->tree_lock);
478  unmap:
479         dax_unmap_atomic(bdev, &dax);
480         return ret;
481 
482  unlock:
483         spin_unlock_irq(&mapping->tree_lock);
484         return ret;
485 }
486 
487 /*
488  * Flush the mapping to the persistent domain within the byte range of [start,
489  * end]. This is required by data integrity operations to ensure file data is
490  * on persistent storage prior to completion of the operation.
491  */
492 int dax_writeback_mapping_range(struct address_space *mapping,
493                 struct block_device *bdev, struct writeback_control *wbc)
494 {
495         struct inode *inode = mapping->host;
496         pgoff_t start_index, end_index, pmd_index;
497         pgoff_t indices[PAGEVEC_SIZE];
498         struct pagevec pvec;
499         bool done = false;
500         int i, ret = 0;
501         void *entry;
502 
503         if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))
504                 return -EIO;
505 
506         if (!mapping->nrexceptional || wbc->sync_mode != WB_SYNC_ALL)
507                 return 0;
508 
509         start_index = wbc->range_start >> PAGE_SHIFT;
510         end_index = wbc->range_end >> PAGE_SHIFT;
511         pmd_index = DAX_PMD_INDEX(start_index);
512 
513         rcu_read_lock();
514         entry = radix_tree_lookup(&mapping->page_tree, pmd_index);
515         rcu_read_unlock();
516 
517         /* see if the start of our range is covered by a PMD entry */
518         if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
519                 start_index = pmd_index;
520 
521         tag_pages_for_writeback(mapping, start_index, end_index);
522 
523         pagevec_init(&pvec, 0);
524         while (!done) {
525                 pvec.nr = find_get_entries_tag(mapping, start_index,
526                                 PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
527                                 pvec.pages, indices);
528 
529                 if (pvec.nr == 0)
530                         break;
531 
532                 for (i = 0; i < pvec.nr; i++) {
533                         if (indices[i] > end_index) {
534                                 done = true;
535                                 break;
536                         }
537 
538                         ret = dax_writeback_one(bdev, mapping, indices[i],
539                                         pvec.pages[i]);
540                         if (ret < 0)
541                                 return ret;
542                 }
543         }
544         wmb_pmem();
545         return 0;
546 }
547 EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
548 
549 static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
550                         struct vm_area_struct *vma, struct vm_fault *vmf)
551 {
552         unsigned long vaddr = (unsigned long)vmf->virtual_address;
553         struct address_space *mapping = inode->i_mapping;
554         struct block_device *bdev = bh->b_bdev;
555         struct blk_dax_ctl dax = {
556                 .sector = to_sector(bh, inode),
557                 .size = bh->b_size,
558         };
559         pgoff_t size;
560         int error;
561 
562         i_mmap_lock_read(mapping);
563 
564         /*
565          * Check truncate didn't happen while we were allocating a block.
566          * If it did, this block may or may not be still allocated to the
567          * file.  We can't tell the filesystem to free it because we can't
568          * take i_mutex here.  In the worst case, the file still has blocks
569          * allocated past the end of the file.
570          */
571         size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
572         if (unlikely(vmf->pgoff >= size)) {
573                 error = -EIO;
574                 goto out;
575         }
576 
577         if (dax_map_atomic(bdev, &dax) < 0) {
578                 error = PTR_ERR(dax.addr);
579                 goto out;
580         }
581 
582         if (buffer_unwritten(bh) || buffer_new(bh)) {
583                 clear_pmem(dax.addr, PAGE_SIZE);
584                 wmb_pmem();
585         }
586         dax_unmap_atomic(bdev, &dax);
587 
588         error = dax_radix_entry(mapping, vmf->pgoff, dax.sector, false,
589                         vmf->flags & FAULT_FLAG_WRITE);
590         if (error)
591                 goto out;
592 
593         error = vm_insert_mixed(vma, vaddr, dax.pfn);
594 
595  out:
596         i_mmap_unlock_read(mapping);
597 
598         return error;
599 }
600 
601 /**
602  * __dax_fault - handle a page fault on a DAX file
603  * @vma: The virtual memory area where the fault occurred
604  * @vmf: The description of the fault
605  * @get_block: The filesystem method used to translate file offsets to blocks
606  * @complete_unwritten: The filesystem method used to convert unwritten blocks
607  *      to written so the data written to them is exposed. This is required for
608  *      required by write faults for filesystems that will return unwritten
609  *      extent mappings from @get_block, but it is optional for reads as
610  *      dax_insert_mapping() will always zero unwritten blocks. If the fs does
611  *      not support unwritten extents, the it should pass NULL.
612  *
613  * When a page fault occurs, filesystems may call this helper in their
614  * fault handler for DAX files. __dax_fault() assumes the caller has done all
615  * the necessary locking for the page fault to proceed successfully.
616  */
617 int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
618                         get_block_t get_block, dax_iodone_t complete_unwritten)
619 {
620         struct file *file = vma->vm_file;
621         struct address_space *mapping = file->f_mapping;
622         struct inode *inode = mapping->host;
623         struct page *page;
624         struct buffer_head bh;
625         unsigned long vaddr = (unsigned long)vmf->virtual_address;
626         unsigned blkbits = inode->i_blkbits;
627         sector_t block;
628         pgoff_t size;
629         int error;
630         int major = 0;
631 
632         size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
633         if (vmf->pgoff >= size)
634                 return VM_FAULT_SIGBUS;
635 
636         memset(&bh, 0, sizeof(bh));
637         block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
638         bh.b_bdev = inode->i_sb->s_bdev;
639         bh.b_size = PAGE_SIZE;
640 
641  repeat:
642         page = find_get_page(mapping, vmf->pgoff);
643         if (page) {
644                 if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
645                         put_page(page);
646                         return VM_FAULT_RETRY;
647                 }
648                 if (unlikely(page->mapping != mapping)) {
649                         unlock_page(page);
650                         put_page(page);
651                         goto repeat;
652                 }
653                 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
654                 if (unlikely(vmf->pgoff >= size)) {
655                         /*
656                          * We have a struct page covering a hole in the file
657                          * from a read fault and we've raced with a truncate
658                          */
659                         error = -EIO;
660                         goto unlock_page;
661                 }
662         }
663 
664         error = get_block(inode, block, &bh, 0);
665         if (!error && (bh.b_size < PAGE_SIZE))
666                 error = -EIO;           /* fs corruption? */
667         if (error)
668                 goto unlock_page;
669 
670         if (!buffer_mapped(&bh) && !buffer_unwritten(&bh) && !vmf->cow_page) {
671                 if (vmf->flags & FAULT_FLAG_WRITE) {
672                         error = get_block(inode, block, &bh, 1);
673                         count_vm_event(PGMAJFAULT);
674                         mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
675                         major = VM_FAULT_MAJOR;
676                         if (!error && (bh.b_size < PAGE_SIZE))
677                                 error = -EIO;
678                         if (error)
679                                 goto unlock_page;
680                 } else {
681                         return dax_load_hole(mapping, page, vmf);
682                 }
683         }
684 
685         if (vmf->cow_page) {
686                 struct page *new_page = vmf->cow_page;
687                 if (buffer_written(&bh))
688                         error = copy_user_bh(new_page, inode, &bh, vaddr);
689                 else
690                         clear_user_highpage(new_page, vaddr);
691                 if (error)
692                         goto unlock_page;
693                 vmf->page = page;
694                 if (!page) {
695                         i_mmap_lock_read(mapping);
696                         /* Check we didn't race with truncate */
697                         size = (i_size_read(inode) + PAGE_SIZE - 1) >>
698                                                                 PAGE_SHIFT;
699                         if (vmf->pgoff >= size) {
700                                 i_mmap_unlock_read(mapping);
701                                 error = -EIO;
702                                 goto out;
703                         }
704                 }
705                 return VM_FAULT_LOCKED;
706         }
707 
708         /* Check we didn't race with a read fault installing a new page */
709         if (!page && major)
710                 page = find_lock_page(mapping, vmf->pgoff);
711 
712         if (page) {
713                 unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
714                                                         PAGE_SIZE, 0);
715                 delete_from_page_cache(page);
716                 unlock_page(page);
717                 put_page(page);
718                 page = NULL;
719         }
720 
721         /*
722          * If we successfully insert the new mapping over an unwritten extent,
723          * we need to ensure we convert the unwritten extent. If there is an
724          * error inserting the mapping, the filesystem needs to leave it as
725          * unwritten to prevent exposure of the stale underlying data to
726          * userspace, but we still need to call the completion function so
727          * the private resources on the mapping buffer can be released. We
728          * indicate what the callback should do via the uptodate variable, same
729          * as for normal BH based IO completions.
730          */
731         error = dax_insert_mapping(inode, &bh, vma, vmf);
732         if (buffer_unwritten(&bh)) {
733                 if (complete_unwritten)
734                         complete_unwritten(&bh, !error);
735                 else
736                         WARN_ON_ONCE(!(vmf->flags & FAULT_FLAG_WRITE));
737         }
738 
739  out:
740         if (error == -ENOMEM)
741                 return VM_FAULT_OOM | major;
742         /* -EBUSY is fine, somebody else faulted on the same PTE */
743         if ((error < 0) && (error != -EBUSY))
744                 return VM_FAULT_SIGBUS | major;
745         return VM_FAULT_NOPAGE | major;
746 
747  unlock_page:
748         if (page) {
749                 unlock_page(page);
750                 put_page(page);
751         }
752         goto out;
753 }
754 EXPORT_SYMBOL(__dax_fault);
755 
756 /**
757  * dax_fault - handle a page fault on a DAX file
758  * @vma: The virtual memory area where the fault occurred
759  * @vmf: The description of the fault
760  * @get_block: The filesystem method used to translate file offsets to blocks
761  *
762  * When a page fault occurs, filesystems may call this helper in their
763  * fault handler for DAX files.
764  */
765 int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
766               get_block_t get_block, dax_iodone_t complete_unwritten)
767 {
768         int result;
769         struct super_block *sb = file_inode(vma->vm_file)->i_sb;
770 
771         if (vmf->flags & FAULT_FLAG_WRITE) {
772                 sb_start_pagefault(sb);
773                 file_update_time(vma->vm_file);
774         }
775         result = __dax_fault(vma, vmf, get_block, complete_unwritten);
776         if (vmf->flags & FAULT_FLAG_WRITE)
777                 sb_end_pagefault(sb);
778 
779         return result;
780 }
781 EXPORT_SYMBOL_GPL(dax_fault);
782 
783 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
784 /*
785  * The 'colour' (ie low bits) within a PMD of a page offset.  This comes up
786  * more often than one might expect in the below function.
787  */
788 #define PG_PMD_COLOUR   ((PMD_SIZE >> PAGE_SHIFT) - 1)
789 
790 static void __dax_dbg(struct buffer_head *bh, unsigned long address,
791                 const char *reason, const char *fn)
792 {
793         if (bh) {
794                 char bname[BDEVNAME_SIZE];
795                 bdevname(bh->b_bdev, bname);
796                 pr_debug("%s: %s addr: %lx dev %s state %lx start %lld "
797                         "length %zd fallback: %s\n", fn, current->comm,
798                         address, bname, bh->b_state, (u64)bh->b_blocknr,
799                         bh->b_size, reason);
800         } else {
801                 pr_debug("%s: %s addr: %lx fallback: %s\n", fn,
802                         current->comm, address, reason);
803         }
804 }
805 
806 #define dax_pmd_dbg(bh, address, reason)        __dax_dbg(bh, address, reason, "dax_pmd")
807 
808 int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
809                 pmd_t *pmd, unsigned int flags, get_block_t get_block,
810                 dax_iodone_t complete_unwritten)
811 {
812         struct file *file = vma->vm_file;
813         struct address_space *mapping = file->f_mapping;
814         struct inode *inode = mapping->host;
815         struct buffer_head bh;
816         unsigned blkbits = inode->i_blkbits;
817         unsigned long pmd_addr = address & PMD_MASK;
818         bool write = flags & FAULT_FLAG_WRITE;
819         struct block_device *bdev;
820         pgoff_t size, pgoff;
821         sector_t block;
822         int error, result = 0;
823         bool alloc = false;
824 
825         /* dax pmd mappings require pfn_t_devmap() */
826         if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
827                 return VM_FAULT_FALLBACK;
828 
829         /* Fall back to PTEs if we're going to COW */
830         if (write && !(vma->vm_flags & VM_SHARED)) {
831                 split_huge_pmd(vma, pmd, address);
832                 dax_pmd_dbg(NULL, address, "cow write");
833                 return VM_FAULT_FALLBACK;
834         }
835         /* If the PMD would extend outside the VMA */
836         if (pmd_addr < vma->vm_start) {
837                 dax_pmd_dbg(NULL, address, "vma start unaligned");
838                 return VM_FAULT_FALLBACK;
839         }
840         if ((pmd_addr + PMD_SIZE) > vma->vm_end) {
841                 dax_pmd_dbg(NULL, address, "vma end unaligned");
842                 return VM_FAULT_FALLBACK;
843         }
844 
845         pgoff = linear_page_index(vma, pmd_addr);
846         size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
847         if (pgoff >= size)
848                 return VM_FAULT_SIGBUS;
849         /* If the PMD would cover blocks out of the file */
850         if ((pgoff | PG_PMD_COLOUR) >= size) {
851                 dax_pmd_dbg(NULL, address,
852                                 "offset + huge page size > file size");
853                 return VM_FAULT_FALLBACK;
854         }
855 
856         memset(&bh, 0, sizeof(bh));
857         bh.b_bdev = inode->i_sb->s_bdev;
858         block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);
859 
860         bh.b_size = PMD_SIZE;
861 
862         if (get_block(inode, block, &bh, 0) != 0)
863                 return VM_FAULT_SIGBUS;
864 
865         if (!buffer_mapped(&bh) && write) {
866                 if (get_block(inode, block, &bh, 1) != 0)
867                         return VM_FAULT_SIGBUS;
868                 alloc = true;
869         }
870 
871         bdev = bh.b_bdev;
872 
873         /*
874          * If the filesystem isn't willing to tell us the length of a hole,
875          * just fall back to PTEs.  Calling get_block 512 times in a loop
876          * would be silly.
877          */
878         if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE) {
879                 dax_pmd_dbg(&bh, address, "allocated block too small");
880                 return VM_FAULT_FALLBACK;
881         }
882 
883         /*
884          * If we allocated new storage, make sure no process has any
885          * zero pages covering this hole
886          */
887         if (alloc) {
888                 loff_t lstart = pgoff << PAGE_SHIFT;
889                 loff_t lend = lstart + PMD_SIZE - 1; /* inclusive */
890 
891                 truncate_pagecache_range(inode, lstart, lend);
892         }
893 
894         i_mmap_lock_read(mapping);
895 
896         /*
897          * If a truncate happened while we were allocating blocks, we may
898          * leave blocks allocated to the file that are beyond EOF.  We can't
899          * take i_mutex here, so just leave them hanging; they'll be freed
900          * when the file is deleted.
901          */
902         size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
903         if (pgoff >= size) {
904                 result = VM_FAULT_SIGBUS;
905                 goto out;
906         }
907         if ((pgoff | PG_PMD_COLOUR) >= size) {
908                 dax_pmd_dbg(&bh, address,
909                                 "offset + huge page size > file size");
910                 goto fallback;
911         }
912 
913         if (!write && !buffer_mapped(&bh) && buffer_uptodate(&bh)) {
914                 spinlock_t *ptl;
915                 pmd_t entry;
916                 struct page *zero_page = get_huge_zero_page();
917 
918                 if (unlikely(!zero_page)) {
919                         dax_pmd_dbg(&bh, address, "no zero page");
920                         goto fallback;
921                 }
922 
923                 ptl = pmd_lock(vma->vm_mm, pmd);
924                 if (!pmd_none(*pmd)) {
925                         spin_unlock(ptl);
926                         dax_pmd_dbg(&bh, address, "pmd already present");
927                         goto fallback;
928                 }
929 
930                 dev_dbg(part_to_dev(bdev->bd_part),
931                                 "%s: %s addr: %lx pfn: <zero> sect: %llx\n",
932                                 __func__, current->comm, address,
933                                 (unsigned long long) to_sector(&bh, inode));
934 
935                 entry = mk_pmd(zero_page, vma->vm_page_prot);
936                 entry = pmd_mkhuge(entry);
937                 set_pmd_at(vma->vm_mm, pmd_addr, pmd, entry);
938                 result = VM_FAULT_NOPAGE;
939                 spin_unlock(ptl);
940         } else {
941                 struct blk_dax_ctl dax = {
942                         .sector = to_sector(&bh, inode),
943                         .size = PMD_SIZE,
944                 };
945                 long length = dax_map_atomic(bdev, &dax);
946 
947                 if (length < 0) {
948                         result = VM_FAULT_SIGBUS;
949                         goto out;
950                 }
951                 if (length < PMD_SIZE) {
952                         dax_pmd_dbg(&bh, address, "dax-length too small");
953                         dax_unmap_atomic(bdev, &dax);
954                         goto fallback;
955                 }
956                 if (pfn_t_to_pfn(dax.pfn) & PG_PMD_COLOUR) {
957                         dax_pmd_dbg(&bh, address, "pfn unaligned");
958                         dax_unmap_atomic(bdev, &dax);
959                         goto fallback;
960                 }
961 
962                 if (!pfn_t_devmap(dax.pfn)) {
963                         dax_unmap_atomic(bdev, &dax);
964                         dax_pmd_dbg(&bh, address, "pfn not in memmap");
965                         goto fallback;
966                 }
967 
968                 if (buffer_unwritten(&bh) || buffer_new(&bh)) {
969                         clear_pmem(dax.addr, PMD_SIZE);
970                         wmb_pmem();
971                         count_vm_event(PGMAJFAULT);
972                         mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
973                         result |= VM_FAULT_MAJOR;
974                 }
975                 dax_unmap_atomic(bdev, &dax);
976 
977                 /*
978                  * For PTE faults we insert a radix tree entry for reads, and
979                  * leave it clean.  Then on the first write we dirty the radix
980                  * tree entry via the dax_pfn_mkwrite() path.  This sequence
981                  * allows the dax_pfn_mkwrite() call to be simpler and avoid a
982                  * call into get_block() to translate the pgoff to a sector in
983                  * order to be able to create a new radix tree entry.
984                  *
985                  * The PMD path doesn't have an equivalent to
986                  * dax_pfn_mkwrite(), though, so for a read followed by a
987                  * write we traverse all the way through __dax_pmd_fault()
988                  * twice.  This means we can just skip inserting a radix tree
989                  * entry completely on the initial read and just wait until
990                  * the write to insert a dirty entry.
991                  */
992                 if (write) {
993                         error = dax_radix_entry(mapping, pgoff, dax.sector,
994                                         true, true);
995                         if (error) {
996                                 dax_pmd_dbg(&bh, address,
997                                                 "PMD radix insertion failed");
998                                 goto fallback;
999                         }
1000                 }
1001 
1002                 dev_dbg(part_to_dev(bdev->bd_part),
1003                                 "%s: %s addr: %lx pfn: %lx sect: %llx\n",
1004                                 __func__, current->comm, address,
1005                                 pfn_t_to_pfn(dax.pfn),
1006                                 (unsigned long long) dax.sector);
1007                 result |= vmf_insert_pfn_pmd(vma, address, pmd,
1008                                 dax.pfn, write);
1009         }
1010 
1011  out:
1012         i_mmap_unlock_read(mapping);
1013 
1014         if (buffer_unwritten(&bh))
1015                 complete_unwritten(&bh, !(result & VM_FAULT_ERROR));
1016 
1017         return result;
1018 
1019  fallback:
1020         count_vm_event(THP_FAULT_FALLBACK);
1021         result = VM_FAULT_FALLBACK;
1022         goto out;
1023 }
1024 EXPORT_SYMBOL_GPL(__dax_pmd_fault);
1025 
1026 /**
1027  * dax_pmd_fault - handle a PMD fault on a DAX file
1028  * @vma: The virtual memory area where the fault occurred
1029  * @vmf: The description of the fault
1030  * @get_block: The filesystem method used to translate file offsets to blocks
1031  *
1032  * When a page fault occurs, filesystems may call this helper in their
1033  * pmd_fault handler for DAX files.
1034  */
1035 int dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
1036                         pmd_t *pmd, unsigned int flags, get_block_t get_block,
1037                         dax_iodone_t complete_unwritten)
1038 {
1039         int result;
1040         struct super_block *sb = file_inode(vma->vm_file)->i_sb;
1041 
1042         if (flags & FAULT_FLAG_WRITE) {
1043                 sb_start_pagefault(sb);
1044                 file_update_time(vma->vm_file);
1045         }
1046         result = __dax_pmd_fault(vma, address, pmd, flags, get_block,
1047                                 complete_unwritten);
1048         if (flags & FAULT_FLAG_WRITE)
1049                 sb_end_pagefault(sb);
1050 
1051         return result;
1052 }
1053 EXPORT_SYMBOL_GPL(dax_pmd_fault);
1054 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
1055 
1056 /**
1057  * dax_pfn_mkwrite - handle first write to DAX page
1058  * @vma: The virtual memory area where the fault occurred
1059  * @vmf: The description of the fault
1060  */
1061 int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
1062 {
1063         struct file *file = vma->vm_file;
1064         int error;
1065 
1066         /*
1067          * We pass NO_SECTOR to dax_radix_entry() because we expect that a
1068          * RADIX_DAX_PTE entry already exists in the radix tree from a
1069          * previous call to __dax_fault().  We just want to look up that PTE
1070          * entry using vmf->pgoff and make sure the dirty tag is set.  This
1071          * saves us from having to make a call to get_block() here to look
1072          * up the sector.
1073          */
1074         error = dax_radix_entry(file->f_mapping, vmf->pgoff, NO_SECTOR, false,
1075                         true);
1076 
1077         if (error == -ENOMEM)
1078                 return VM_FAULT_OOM;
1079         if (error)
1080                 return VM_FAULT_SIGBUS;
1081         return VM_FAULT_NOPAGE;
1082 }
1083 EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
1084 
1085 /**
1086  * dax_zero_page_range - zero a range within a page of a DAX file
1087  * @inode: The file being truncated
1088  * @from: The file offset that is being truncated to
1089  * @length: The number of bytes to zero
1090  * @get_block: The filesystem method used to translate file offsets to blocks
1091  *
1092  * This function can be called by a filesystem when it is zeroing part of a
1093  * page in a DAX file.  This is intended for hole-punch operations.  If
1094  * you are truncating a file, the helper function dax_truncate_page() may be
1095  * more convenient.
1096  *
1097  * We work in terms of PAGE_SIZE here for commonality with
1098  * block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
1099  * took care of disposing of the unnecessary blocks.  Even if the filesystem
1100  * block size is smaller than PAGE_SIZE, we have to zero the rest of the page
1101  * since the file might be mmapped.
1102  */
1103 int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
1104                                                         get_block_t get_block)
1105 {
1106         struct buffer_head bh;
1107         pgoff_t index = from >> PAGE_SHIFT;
1108         unsigned offset = from & (PAGE_SIZE-1);
1109         int err;
1110 
1111         /* Block boundary? Nothing to do */
1112         if (!length)
1113                 return 0;
1114         BUG_ON((offset + length) > PAGE_SIZE);
1115 
1116         memset(&bh, 0, sizeof(bh));
1117         bh.b_bdev = inode->i_sb->s_bdev;
1118         bh.b_size = PAGE_SIZE;
1119         err = get_block(inode, index, &bh, 0);
1120         if (err < 0)
1121                 return err;
1122         if (buffer_written(&bh)) {
1123                 struct block_device *bdev = bh.b_bdev;
1124                 struct blk_dax_ctl dax = {
1125                         .sector = to_sector(&bh, inode),
1126                         .size = PAGE_SIZE,
1127                 };
1128 
1129                 if (dax_map_atomic(bdev, &dax) < 0)
1130                         return PTR_ERR(dax.addr);
1131                 clear_pmem(dax.addr + offset, length);
1132                 wmb_pmem();
1133                 dax_unmap_atomic(bdev, &dax);
1134         }
1135 
1136         return 0;
1137 }
1138 EXPORT_SYMBOL_GPL(dax_zero_page_range);
1139 
1140 /**
1141  * dax_truncate_page - handle a partial page being truncated in a DAX file
1142  * @inode: The file being truncated
1143  * @from: The file offset that is being truncated to
1144  * @get_block: The filesystem method used to translate file offsets to blocks
1145  *
1146  * Similar to block_truncate_page(), this function can be called by a
1147  * filesystem when it is truncating a DAX file to handle the partial page.
1148  *
1149  * We work in terms of PAGE_SIZE here for commonality with
1150  * block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
1151  * took care of disposing of the unnecessary blocks.  Even if the filesystem
1152  * block size is smaller than PAGE_SIZE, we have to zero the rest of the page
1153  * since the file might be mmapped.
1154  */
1155 int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
1156 {
1157         unsigned length = PAGE_ALIGN(from) - from;
1158         return dax_zero_page_range(inode, from, length, get_block);
1159 }
1160 EXPORT_SYMBOL_GPL(dax_truncate_page);
1161 

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