fs/dax.c - kernel/common - Git at Google

 /*
  * fs/dax.c - Direct Access filesystem code
  * Copyright (c) 2013-2014 Intel Corporation
  * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
  * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
  * version 2, as published by the Free Software Foundation.
  *
  * This program is distributed in the hope it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  * more details.
  */

 #include <linux/atomic.h>
 #include <linux/blkdev.h>
 #include <linux/buffer_head.h>
 #include <linux/dax.h>
 #include <linux/fs.h>
 #include <linux/genhd.h>
 #include <linux/highmem.h>
 #include <linux/memcontrol.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
 #include <linux/pagevec.h>
 #include <linux/sched.h>
 #include <linux/sched/signal.h>
 #include <linux/uio.h>
 #include <linux/vmstat.h>
 #include <linux/pfn_t.h>
 #include <linux/sizes.h>
 #include <linux/mmu_notifier.h>
 #include <linux/iomap.h>
 #include "internal.h"

 #define CREATE_TRACE_POINTS
 #include <trace/events/fs_dax.h>

 /* We choose 4096 entries - same as per-zone page wait tables */
 #define DAX_WAIT_TABLE_BITS 12
 #define DAX_WAIT_TABLE_ENTRIES (1 << DAX_WAIT_TABLE_BITS)

 /* The 'colour' (ie low bits) within a PMD of a page offset.  */
 #define PG_PMD_COLOUR	((PMD_SIZE >> PAGE_SHIFT) - 1)

 static wait_queue_head_t wait_table[DAX_WAIT_TABLE_ENTRIES];

 static int __init init_dax_wait_table(void)
 {
 	int i;

 	for (i = 0; i < DAX_WAIT_TABLE_ENTRIES; i++)
 		init_waitqueue_head(wait_table + i);
 	return 0;
 }
 fs_initcall(init_dax_wait_table);

 /*
  * We use lowest available bit in exceptional entry for locking, one bit for
  * the entry size (PMD) and two more to tell us if the entry is a zero page or
  * an empty entry that is just used for locking.  In total four special bits.
  *
  * If the PMD bit isn't set the entry has size PAGE_SIZE, and if the ZERO_PAGE
  * and EMPTY bits aren't set the entry is a normal DAX entry with a filesystem
  * block allocation.
  */
 #define RADIX_DAX_SHIFT		(RADIX_TREE_EXCEPTIONAL_SHIFT + 4)
 #define RADIX_DAX_ENTRY_LOCK	(1 << RADIX_TREE_EXCEPTIONAL_SHIFT)
 #define RADIX_DAX_PMD		(1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 1))
 #define RADIX_DAX_ZERO_PAGE	(1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 2))
 #define RADIX_DAX_EMPTY		(1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 3))

 static unsigned long dax_radix_sector(void *entry)
 {
 	return (unsigned long)entry >> RADIX_DAX_SHIFT;
 }

 static void *dax_radix_locked_entry(sector_t sector, unsigned long flags)
 {
 	return (void *)(RADIX_TREE_EXCEPTIONAL_ENTRY | flags |
 			((unsigned long)sector << RADIX_DAX_SHIFT) |
 			RADIX_DAX_ENTRY_LOCK);
 }

 static unsigned int dax_radix_order(void *entry)
 {
 	if ((unsigned long)entry & RADIX_DAX_PMD)
 		return PMD_SHIFT - PAGE_SHIFT;
 	return 0;
 }

 static int dax_is_pmd_entry(void *entry)
 {
 	return (unsigned long)entry & RADIX_DAX_PMD;
 }

 static int dax_is_pte_entry(void *entry)
 {
 	return !((unsigned long)entry & RADIX_DAX_PMD);
 }

 static int dax_is_zero_entry(void *entry)
 {
 	return (unsigned long)entry & RADIX_DAX_ZERO_PAGE;
 }

 static int dax_is_empty_entry(void *entry)
 {
 	return (unsigned long)entry & RADIX_DAX_EMPTY;
 }

 /*
  * DAX radix tree locking
  */
 struct exceptional_entry_key {
 	struct address_space *mapping;
 	pgoff_t entry_start;
 };

 struct wait_exceptional_entry_queue {
 	wait_queue_entry_t wait;
 	struct exceptional_entry_key key;
 };

 static wait_queue_head_t *dax_entry_waitqueue(struct address_space *mapping,
 		pgoff_t index, void *entry, struct exceptional_entry_key *key)
 {
 	unsigned long hash;

 	/*
 	 * If 'entry' is a PMD, align the 'index' that we use for the wait
 	 * queue to the start of that PMD.  This ensures that all offsets in
 	 * the range covered by the PMD map to the same bit lock.
 	 */
 	if (dax_is_pmd_entry(entry))
 		index &= ~PG_PMD_COLOUR;

 	key->mapping = mapping;
 	key->entry_start = index;

 	hash = hash_long((unsigned long)mapping ^ index, DAX_WAIT_TABLE_BITS);
 	return wait_table + hash;
 }

 static int wake_exceptional_entry_func(wait_queue_entry_t *wait, unsigned int mode,
 				       int sync, void *keyp)
 {
 	struct exceptional_entry_key *key = keyp;
 	struct wait_exceptional_entry_queue *ewait =
 		container_of(wait, struct wait_exceptional_entry_queue, wait);

 	if (key->mapping != ewait->key.mapping ||
 	    key->entry_start != ewait->key.entry_start)
 		return 0;
 	return autoremove_wake_function(wait, mode, sync, NULL);
 }

 /*
  * We do not necessarily hold the mapping->tree_lock when we call this
  * function so it is possible that 'entry' is no longer a valid item in the
  * radix tree.  This is okay because all we really need to do is to find the
  * correct waitqueue where tasks might be waiting for that old 'entry' and
  * wake them.
  */
 static void dax_wake_mapping_entry_waiter(struct address_space *mapping,
 		pgoff_t index, void *entry, bool wake_all)
 {
 	struct exceptional_entry_key key;
 	wait_queue_head_t *wq;

 	wq = dax_entry_waitqueue(mapping, index, entry, &key);

 	/*
 	 * Checking for locked entry and prepare_to_wait_exclusive() happens
 	 * under mapping->tree_lock, ditto for entry handling in our callers.
 	 * So at this point all tasks that could have seen our entry locked
 	 * must be in the waitqueue and the following check will see them.
 	 */
 	if (waitqueue_active(wq))
 		__wake_up(wq, TASK_NORMAL, wake_all ? 0 : 1, &key);
 }

 /*
  * Check whether the given slot is locked. The function must be called with
  * mapping->tree_lock held
  */
 static inline int slot_locked(struct address_space *mapping, void **slot)
 {
 	unsigned long entry = (unsigned long)
 		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
 	return entry & RADIX_DAX_ENTRY_LOCK;
 }

 /*
  * Mark the given slot is locked. The function must be called with
  * mapping->tree_lock held
  */
 static inline void *lock_slot(struct address_space *mapping, void **slot)
 {
 	unsigned long entry = (unsigned long)
 		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);

 	entry |= RADIX_DAX_ENTRY_LOCK;
 	radix_tree_replace_slot(&mapping->page_tree, slot, (void *)entry);
 	return (void *)entry;
 }

 /*
  * Mark the given slot is unlocked. The function must be called with
  * mapping->tree_lock held
  */
 static inline void *unlock_slot(struct address_space *mapping, void **slot)
 {
 	unsigned long entry = (unsigned long)
 		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);

 	entry &= ~(unsigned long)RADIX_DAX_ENTRY_LOCK;
 	radix_tree_replace_slot(&mapping->page_tree, slot, (void *)entry);
 	return (void *)entry;
 }

 /*
  * Lookup entry in radix tree, wait for it to become unlocked if it is
  * exceptional entry and return it. The caller must call
  * put_unlocked_mapping_entry() when he decided not to lock the entry or
  * put_locked_mapping_entry() when he locked the entry and now wants to
  * unlock it.
  *
  * The function must be called with mapping->tree_lock held.
  */
 static void *get_unlocked_mapping_entry(struct address_space *mapping,
 					pgoff_t index, void ***slotp)
 {
 	void *entry, **slot;
 	struct wait_exceptional_entry_queue ewait;
 	wait_queue_head_t *wq;

 	init_wait(&ewait.wait);
 	ewait.wait.func = wake_exceptional_entry_func;

 	for (;;) {
 		entry = __radix_tree_lookup(&mapping->page_tree, index, NULL,
 					  &slot);
 		if (!entry ||
 		    WARN_ON_ONCE(!radix_tree_exceptional_entry(entry)) ||
 		    !slot_locked(mapping, slot)) {
 			if (slotp)
 				*slotp = slot;
 			return entry;
 		}

 		wq = dax_entry_waitqueue(mapping, index, entry, &ewait.key);
 		prepare_to_wait_exclusive(wq, &ewait.wait,
 					  TASK_UNINTERRUPTIBLE);
 		spin_unlock_irq(&mapping->tree_lock);
 		schedule();
 		finish_wait(wq, &ewait.wait);
 		spin_lock_irq(&mapping->tree_lock);
 	}
 }

 static void dax_unlock_mapping_entry(struct address_space *mapping,
 				     pgoff_t index)
 {
 	void *entry, **slot;

 	spin_lock_irq(&mapping->tree_lock);
 	entry = __radix_tree_lookup(&mapping->page_tree, index, NULL, &slot);
 	if (WARN_ON_ONCE(!entry || !radix_tree_exceptional_entry(entry) ||
 			 !slot_locked(mapping, slot))) {
 		spin_unlock_irq(&mapping->tree_lock);
 		return;
 	}
 	unlock_slot(mapping, slot);
 	spin_unlock_irq(&mapping->tree_lock);
 	dax_wake_mapping_entry_waiter(mapping, index, entry, false);
 }

 static void put_locked_mapping_entry(struct address_space *mapping,
 		pgoff_t index)
 {
 	dax_unlock_mapping_entry(mapping, index);
 }

 /*
  * Called when we are done with radix tree entry we looked up via
  * get_unlocked_mapping_entry() and which we didn't lock in the end.
  */
 static void put_unlocked_mapping_entry(struct address_space *mapping,
 				       pgoff_t index, void *entry)
 {
 	if (!entry)
 		return;

 	/* We have to wake up next waiter for the radix tree entry lock */
 	dax_wake_mapping_entry_waiter(mapping, index, entry, false);
 }

 /*
  * Find radix tree entry at given index. If it points to an exceptional entry,
  * return it with the radix tree entry locked. If the radix tree doesn't
  * contain given index, create an empty exceptional entry for the index and
  * return with it locked.
  *
  * When requesting an entry with size RADIX_DAX_PMD, grab_mapping_entry() will
  * either return that locked entry or will return an error.  This error will
  * happen if there are any 4k entries within the 2MiB range that we are
  * requesting.
  *
  * We always favor 4k entries over 2MiB entries. There isn't a flow where we
  * evict 4k entries in order to 'upgrade' them to a 2MiB entry.  A 2MiB
  * insertion will fail if it finds any 4k entries already in the tree, and a
  * 4k insertion will cause an existing 2MiB entry to be unmapped and
  * downgraded to 4k entries.  This happens for both 2MiB huge zero pages as
  * well as 2MiB empty entries.
  *
  * The exception to this downgrade path is for 2MiB DAX PMD entries that have
  * real storage backing them.  We will leave these real 2MiB DAX entries in
  * the tree, and PTE writes will simply dirty the entire 2MiB DAX entry.
  *
  * Note: Unlike filemap_fault() we don't honor FAULT_FLAG_RETRY flags. For
  * persistent memory the benefit is doubtful. We can add that later if we can
  * show it helps.
  */
 static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index,
 		unsigned long size_flag)
 {
 	bool pmd_downgrade = false; /* splitting 2MiB entry into 4k entries? */
 	void *entry, **slot;

 restart:
 	spin_lock_irq(&mapping->tree_lock);
 	entry = get_unlocked_mapping_entry(mapping, index, &slot);

 	if (WARN_ON_ONCE(entry && !radix_tree_exceptional_entry(entry))) {
 		entry = ERR_PTR(-EIO);
 		goto out_unlock;
 	}

 	if (entry) {
 		if (size_flag & RADIX_DAX_PMD) {
 			if (dax_is_pte_entry(entry)) {
 				put_unlocked_mapping_entry(mapping, index,
 						entry);
 				entry = ERR_PTR(-EEXIST);
 				goto out_unlock;
 			}
 		} else { /* trying to grab a PTE entry */
 			if (dax_is_pmd_entry(entry) &&
 			    (dax_is_zero_entry(entry) ||
 			     dax_is_empty_entry(entry))) {
 				pmd_downgrade = true;
 			}
 		}
 	}

 	/* No entry for given index? Make sure radix tree is big enough. */
 	if (!entry || pmd_downgrade) {
 		int err;

 		if (pmd_downgrade) {
 			/*
 			 * Make sure 'entry' remains valid while we drop
 			 * mapping->tree_lock.
 			 */
 			entry = lock_slot(mapping, slot);
 		}

 		spin_unlock_irq(&mapping->tree_lock);
 		/*
 		 * Besides huge zero pages the only other thing that gets
 		 * downgraded are empty entries which don't need to be
 		 * unmapped.
 		 */
 		if (pmd_downgrade && dax_is_zero_entry(entry))
 			unmap_mapping_range(mapping,
 				(index << PAGE_SHIFT) & PMD_MASK, PMD_SIZE, 0);

 		err = radix_tree_preload(
 				mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM);
 		if (err) {
 			if (pmd_downgrade)
 				put_locked_mapping_entry(mapping, index);
 			return ERR_PTR(err);
 		}
 		spin_lock_irq(&mapping->tree_lock);

 		if (!entry) {
 			/*
 			 * We needed to drop the page_tree lock while calling
 			 * radix_tree_preload() and we didn't have an entry to
 			 * lock.  See if another thread inserted an entry at
 			 * our index during this time.
 			 */
 			entry = __radix_tree_lookup(&mapping->page_tree, index,
 					NULL, &slot);
 			if (entry) {
 				radix_tree_preload_end();
 				spin_unlock_irq(&mapping->tree_lock);
 				goto restart;
 			}
 		}

 		if (pmd_downgrade) {
 			radix_tree_delete(&mapping->page_tree, index);
 			mapping->nrexceptional--;
 			dax_wake_mapping_entry_waiter(mapping, index, entry,
 					true);
 		}

 		entry = dax_radix_locked_entry(0, size_flag | RADIX_DAX_EMPTY);

 		err = __radix_tree_insert(&mapping->page_tree, index,
 				dax_radix_order(entry), entry);
 		radix_tree_preload_end();
 		if (err) {
 			spin_unlock_irq(&mapping->tree_lock);
 			/*
 			 * Our insertion of a DAX entry failed, most likely
 			 * because we were inserting a PMD entry and it
 			 * collided with a PTE sized entry at a different
 			 * index in the PMD range.  We haven't inserted
 			 * anything into the radix tree and have no waiters to
 			 * wake.
 			 */
 			return ERR_PTR(err);
 		}
 		/* Good, we have inserted empty locked entry into the tree. */
 		mapping->nrexceptional++;
 		spin_unlock_irq(&mapping->tree_lock);
 		return entry;
 	}
 	entry = lock_slot(mapping, slot);
  out_unlock:
 	spin_unlock_irq(&mapping->tree_lock);
 	return entry;
 }

 static int __dax_invalidate_mapping_entry(struct address_space *mapping,
 					  pgoff_t index, bool trunc)
 {
 	int ret = 0;
 	void *entry;
 	struct radix_tree_root *page_tree = &mapping->page_tree;

 	spin_lock_irq(&mapping->tree_lock);
 	entry = get_unlocked_mapping_entry(mapping, index, NULL);
 	if (!entry || WARN_ON_ONCE(!radix_tree_exceptional_entry(entry)))
 		goto out;
 	if (!trunc &&
 	    (radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_DIRTY) ||
 	     radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE)))
 		goto out;
 	radix_tree_delete(page_tree, index);
 	mapping->nrexceptional--;
 	ret = 1;
 out:
 	put_unlocked_mapping_entry(mapping, index, entry);
 	spin_unlock_irq(&mapping->tree_lock);
 	return ret;
 }
 /*
  * Delete exceptional DAX entry at @index from @mapping. Wait for radix tree
  * entry to get unlocked before deleting it.
  */
 int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
 {
 	int ret = __dax_invalidate_mapping_entry(mapping, index, true);

 	/*
 	 * This gets called from truncate / punch_hole path. As such, the caller
 	 * must hold locks protecting against concurrent modifications of the
 	 * radix tree (usually fs-private i_mmap_sem for writing). Since the
 	 * caller has seen exceptional entry for this index, we better find it
 	 * at that index as well...
 	 */
 	WARN_ON_ONCE(!ret);
 	return ret;
 }

 /*
  * Invalidate exceptional DAX entry if it is clean.
  */
 int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
 				      pgoff_t index)
 {
 	return __dax_invalidate_mapping_entry(mapping, index, false);
 }

 static int copy_user_dax(struct block_device *bdev, struct dax_device *dax_dev,
 		sector_t sector, size_t size, struct page *to,
 		unsigned long vaddr)
 {
 	void *vto, *kaddr;
 	pgoff_t pgoff;
 	pfn_t pfn;
 	long rc;
 	int id;

 	rc = bdev_dax_pgoff(bdev, sector, size, &pgoff);
 	if (rc)
 		return rc;

 	id = dax_read_lock();
 	rc = dax_direct_access(dax_dev, pgoff, PHYS_PFN(size), &kaddr, &pfn);
 	if (rc < 0) {
 		dax_read_unlock(id);
 		return rc;
 	}
 	vto = kmap_atomic(to);
 	copy_user_page(vto, (void __force *)kaddr, vaddr, to);
 	kunmap_atomic(vto);
 	dax_read_unlock(id);
 	return 0;
 }

 /*
  * By this point grab_mapping_entry() has ensured that we have a locked entry
  * of the appropriate size so we don't have to worry about downgrading PMDs to
  * PTEs.  If we happen to be trying to insert a PTE and there is a PMD
  * already in the tree, we will skip the insertion and just dirty the PMD as
  * appropriate.
  */
 static void *dax_insert_mapping_entry(struct address_space *mapping,
 				      struct vm_fault *vmf,
 				      void *entry, sector_t sector,
 				      unsigned long flags)
 {
 	struct radix_tree_root *page_tree = &mapping->page_tree;
 	void *new_entry;
 	pgoff_t index = vmf->pgoff;

 	if (vmf->flags & FAULT_FLAG_WRITE)
 		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);

 	if (dax_is_zero_entry(entry) && !(flags & RADIX_DAX_ZERO_PAGE)) {
 		/* we are replacing a zero page with block mapping */
 		if (dax_is_pmd_entry(entry))
 			unmap_mapping_range(mapping,
 					(vmf->pgoff << PAGE_SHIFT) & PMD_MASK,
 					PMD_SIZE, 0);
 		else /* pte entry */
 			unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
 					PAGE_SIZE, 0);
 	}

 	spin_lock_irq(&mapping->tree_lock);
 	new_entry = dax_radix_locked_entry(sector, flags);

 	if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
 		/*
 		 * Only swap our new entry into the radix tree if the current
 		 * entry is a zero page or an empty entry.  If a normal PTE or
 		 * PMD entry is already in the tree, we leave it alone.  This
 		 * means that if we are trying to insert a PTE and the
 		 * existing entry is a PMD, we will just leave the PMD in the
 		 * tree and dirty it if necessary.
 		 */
 		struct radix_tree_node *node;
 		void **slot;
 		void *ret;

 		ret = __radix_tree_lookup(page_tree, index, &node, &slot);
 		WARN_ON_ONCE(ret != entry);
 		__radix_tree_replace(page_tree, node, slot,
 				     new_entry, NULL, NULL);
 		entry = new_entry;
 	}

 	if (vmf->flags & FAULT_FLAG_WRITE)
 		radix_tree_tag_set(page_tree, index, PAGECACHE_TAG_DIRTY);

 	spin_unlock_irq(&mapping->tree_lock);
 	return entry;
 }

 static inline unsigned long
 pgoff_address(pgoff_t pgoff, struct vm_area_struct *vma)
 {
 	unsigned long address;

 	address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
 	VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
 	return address;
 }

 /* Walk all mappings of a given index of a file and writeprotect them */
 static void dax_mapping_entry_mkclean(struct address_space *mapping,
 				      pgoff_t index, unsigned long pfn)
 {
 	struct vm_area_struct *vma;
 	pte_t pte, *ptep = NULL;
 	pmd_t *pmdp = NULL;
 	spinlock_t *ptl;

 	i_mmap_lock_read(mapping);
 	vma_interval_tree_foreach(vma, &mapping->i_mmap, index, index) {
 		unsigned long address, start, end;

 		cond_resched();

 		if (!(vma->vm_flags & VM_SHARED))
 			continue;

 		address = pgoff_address(index, vma);

 		/*
 		 * Note because we provide start/end to follow_pte_pmd it will
 		 * call mmu_notifier_invalidate_range_start() on our behalf
 		 * before taking any lock.
 		 */
 		if (follow_pte_pmd(vma->vm_mm, address, &start, &end, &ptep, &pmdp, &ptl))
 			continue;

 		if (pmdp) {
 #ifdef CONFIG_FS_DAX_PMD
 			pmd_t pmd;

 			if (pfn != pmd_pfn(*pmdp))
 				goto unlock_pmd;
 			if (!pmd_dirty(*pmdp) && !pmd_write(*pmdp))
 				goto unlock_pmd;

 			flush_cache_page(vma, address, pfn);
 			pmd = pmdp_huge_clear_flush(vma, address, pmdp);
 			pmd = pmd_wrprotect(pmd);
 			pmd = pmd_mkclean(pmd);
 			set_pmd_at(vma->vm_mm, address, pmdp, pmd);
 			mmu_notifier_invalidate_range(vma->vm_mm, start, end);
 unlock_pmd:
 #endif
 			spin_unlock(ptl);
 		} else {
 			if (pfn != pte_pfn(*ptep))
 				goto unlock_pte;
 			if (!pte_dirty(*ptep) && !pte_write(*ptep))
 				goto unlock_pte;

 			flush_cache_page(vma, address, pfn);
 			pte = ptep_clear_flush(vma, address, ptep);
 			pte = pte_wrprotect(pte);
 			pte = pte_mkclean(pte);
 			set_pte_at(vma->vm_mm, address, ptep, pte);
 			mmu_notifier_invalidate_range(vma->vm_mm, start, end);
 unlock_pte:
 			pte_unmap_unlock(ptep, ptl);
 		}

 		mmu_notifier_invalidate_range_end(vma->vm_mm, start, end);
 	}
 	i_mmap_unlock_read(mapping);
 }

 static int dax_writeback_one(struct block_device *bdev,
 		struct dax_device *dax_dev, struct address_space *mapping,
 		pgoff_t index, void *entry)
 {
 	struct radix_tree_root *page_tree = &mapping->page_tree;
 	void *entry2, **slot, *kaddr;
 	long ret = 0, id;
 	sector_t sector;
 	pgoff_t pgoff;
 	size_t size;
 	pfn_t pfn;

 	/*
 	 * A page got tagged dirty in DAX mapping? Something is seriously
 	 * wrong.
 	 */
 	if (WARN_ON(!radix_tree_exceptional_entry(entry)))
 		return -EIO;

 	spin_lock_irq(&mapping->tree_lock);
 	entry2 = get_unlocked_mapping_entry(mapping, index, &slot);
 	/* Entry got punched out / reallocated? */
 	if (!entry2 || WARN_ON_ONCE(!radix_tree_exceptional_entry(entry2)))
 		goto put_unlocked;
 	/*
 	 * Entry got reallocated elsewhere? No need to writeback. We have to
 	 * compare sectors as we must not bail out due to difference in lockbit
 	 * or entry type.
 	 */
 	if (dax_radix_sector(entry2) != dax_radix_sector(entry))
 		goto put_unlocked;
 	if (WARN_ON_ONCE(dax_is_empty_entry(entry) ||
 				dax_is_zero_entry(entry))) {
 		ret = -EIO;
 		goto put_unlocked;
 	}

 	/* Another fsync thread may have already written back this entry */
 	if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
 		goto put_unlocked;
 	/* Lock the entry to serialize with page faults */
 	entry = lock_slot(mapping, slot);
 	/*
 	 * We can clear the tag now but we have to be careful so that concurrent
 	 * dax_writeback_one() calls for the same index cannot finish before we
 	 * actually flush the caches. This is achieved as the calls will look
 	 * at the entry only under tree_lock and once they do that they will
 	 * see the entry locked and wait for it to unlock.
 	 */
 	radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
 	spin_unlock_irq(&mapping->tree_lock);

 	/*
 	 * Even if dax_writeback_mapping_range() was given a wbc->range_start
 	 * in the middle of a PMD, the 'index' we are given will be aligned to
 	 * the start index of the PMD, as will the sector we pull from
 	 * 'entry'.  This allows us to flush for PMD_SIZE and not have to
 	 * worry about partial PMD writebacks.
 	 */
 	sector = dax_radix_sector(entry);
 	size = PAGE_SIZE << dax_radix_order(entry);

 	id = dax_read_lock();
 	ret = bdev_dax_pgoff(bdev, sector, size, &pgoff);
 	if (ret)
 		goto dax_unlock;

 	/*
 	 * dax_direct_access() may sleep, so cannot hold tree_lock over
 	 * its invocation.
 	 */
 	ret = dax_direct_access(dax_dev, pgoff, size / PAGE_SIZE, &kaddr, &pfn);
 	if (ret < 0)
 		goto dax_unlock;

 	if (WARN_ON_ONCE(ret < size / PAGE_SIZE)) {
 		ret = -EIO;
 		goto dax_unlock;
 	}

 	dax_mapping_entry_mkclean(mapping, index, pfn_t_to_pfn(pfn));
 	dax_flush(dax_dev, kaddr, size);
 	/*
 	 * After we have flushed the cache, we can clear the dirty tag. There
 	 * cannot be new dirty data in the pfn after the flush has completed as
 	 * the pfn mappings are writeprotected and fault waits for mapping
 	 * entry lock.
 	 */
 	spin_lock_irq(&mapping->tree_lock);
 	radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_DIRTY);
 	spin_unlock_irq(&mapping->tree_lock);
 	trace_dax_writeback_one(mapping->host, index, size >> PAGE_SHIFT);
  dax_unlock:
 	dax_read_unlock(id);
 	put_locked_mapping_entry(mapping, index);
 	return ret;

  put_unlocked:
 	put_unlocked_mapping_entry(mapping, index, entry2);
 	spin_unlock_irq(&mapping->tree_lock);
 	return ret;
 }

 /*
  * Flush the mapping to the persistent domain within the byte range of [start,
  * end]. This is required by data integrity operations to ensure file data is
  * on persistent storage prior to completion of the operation.
  */
 int dax_writeback_mapping_range(struct address_space *mapping,
 		struct block_device *bdev, struct writeback_control *wbc)
 {
 	struct inode *inode = mapping->host;
 	pgoff_t start_index, end_index;
 	pgoff_t indices[PAGEVEC_SIZE];
 	struct dax_device *dax_dev;
 	struct pagevec pvec;
 	bool done = false;
 	int i, ret = 0;

 	if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))
 		return -EIO;

 	if (!mapping->nrexceptional || wbc->sync_mode != WB_SYNC_ALL)
 		return 0;

 	dax_dev = dax_get_by_host(bdev->bd_disk->disk_name);
 	if (!dax_dev)
 		return -EIO;

 	start_index = wbc->range_start >> PAGE_SHIFT;
 	end_index = wbc->range_end >> PAGE_SHIFT;

 	trace_dax_writeback_range(inode, start_index, end_index);

 	tag_pages_for_writeback(mapping, start_index, end_index);

 	pagevec_init(&pvec, 0);
 	while (!done) {
 		pvec.nr = find_get_entries_tag(mapping, start_index,
 				PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
 				pvec.pages, indices);

 		if (pvec.nr == 0)
 			break;

 		for (i = 0; i < pvec.nr; i++) {
 			if (indices[i] > end_index) {
 				done = true;
 				break;
 			}

 			ret = dax_writeback_one(bdev, dax_dev, mapping,
 					indices[i], pvec.pages[i]);
 			if (ret < 0) {
 				mapping_set_error(mapping, ret);
 				goto out;
 			}
 		}
 		start_index = indices[pvec.nr - 1] + 1;
 	}
 out:
 	put_dax(dax_dev);
 	trace_dax_writeback_range_done(inode, start_index, end_index);
 	return (ret < 0 ? ret : 0);
 }
 EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);

 static int dax_insert_mapping(struct address_space *mapping,
 		struct block_device *bdev, struct dax_device *dax_dev,
 		sector_t sector, size_t size, void *entry,
 		struct vm_area_struct *vma, struct vm_fault *vmf)
 {
 	unsigned long vaddr = vmf->address;
 	void *ret, *kaddr;
 	pgoff_t pgoff;
 	int id, rc;
 	pfn_t pfn;

 	rc = bdev_dax_pgoff(bdev, sector, size, &pgoff);
 	if (rc)
 		return rc;

 	id = dax_read_lock();
 	rc = dax_direct_access(dax_dev, pgoff, PHYS_PFN(size), &kaddr, &pfn);
 	if (rc < 0) {
 		dax_read_unlock(id);
 		return rc;
 	}
 	dax_read_unlock(id);

 	ret = dax_insert_mapping_entry(mapping, vmf, entry, sector, 0);
 	if (IS_ERR(ret))
 		return PTR_ERR(ret);

 	trace_dax_insert_mapping(mapping->host, vmf, ret);
 	if (vmf->flags & FAULT_FLAG_WRITE)
 		return vm_insert_mixed_mkwrite(vma, vaddr, pfn);
 	else
 		return vm_insert_mixed(vma, vaddr, pfn);
 }

 /*
  * The user has performed a load from a hole in the file.  Allocating a new
  * page in the file would cause excessive storage usage for workloads with
  * sparse files.  Instead we insert a read-only mapping of the 4k zero page.
  * If this page is ever written to we will re-fault and change the mapping to
  * point to real DAX storage instead.
  */
 static int dax_load_hole(struct address_space *mapping, void *entry,
 			 struct vm_fault *vmf)
 {
 	struct inode *inode = mapping->host;
 	unsigned long vaddr = vmf->address;
 	int ret = VM_FAULT_NOPAGE;
 	struct page *zero_page;
 	void *entry2;

 	zero_page = ZERO_PAGE(0);
 	if (unlikely(!zero_page)) {
 		ret = VM_FAULT_OOM;
 		goto out;
 	}

 	entry2 = dax_insert_mapping_entry(mapping, vmf, entry, 0,
 			RADIX_DAX_ZERO_PAGE);
 	if (IS_ERR(entry2)) {
 		ret = VM_FAULT_SIGBUS;
 		goto out;
 	}

 	vm_insert_mixed(vmf->vma, vaddr, page_to_pfn_t(zero_page));
 out:
 	trace_dax_load_hole(inode, vmf, ret);
 	return ret;
 }

 static bool dax_range_is_aligned(struct block_device *bdev,
 				 unsigned int offset, unsigned int length)
 {
 	unsigned short sector_size = bdev_logical_block_size(bdev);

 	if (!IS_ALIGNED(offset, sector_size))
 		return false;
 	if (!IS_ALIGNED(length, sector_size))
 		return false;

 	return true;
 }

 int __dax_zero_page_range(struct block_device *bdev,
 		struct dax_device *dax_dev, sector_t sector,
 		unsigned int offset, unsigned int size)
 {
 	if (dax_range_is_aligned(bdev, offset, size)) {
 		sector_t start_sector = sector + (offset >> 9);

 		return blkdev_issue_zeroout(bdev, start_sector,
 				size >> 9, GFP_NOFS, 0);
 	} else {
 		pgoff_t pgoff;
 		long rc, id;
 		void *kaddr;
 		pfn_t pfn;

 		rc = bdev_dax_pgoff(bdev, sector, PAGE_SIZE, &pgoff);
 		if (rc)
 			return rc;

 		id = dax_read_lock();
 		rc = dax_direct_access(dax_dev, pgoff, 1, &kaddr,
 				&pfn);
 		if (rc < 0) {
 			dax_read_unlock(id);
 			return rc;
 		}
 		memset(kaddr + offset, 0, size);
 		dax_flush(dax_dev, kaddr + offset, size);
 		dax_read_unlock(id);
 	}
 	return 0;
 }
 EXPORT_SYMBOL_GPL(__dax_zero_page_range);

 static sector_t dax_iomap_sector(struct iomap *iomap, loff_t pos)
 {
 	return iomap->blkno + (((pos & PAGE_MASK) - iomap->offset) >> 9);
 }

 static loff_t
 dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 		struct iomap *iomap)
 {
 	struct block_device *bdev = iomap->bdev;
 	struct dax_device *dax_dev = iomap->dax_dev;
 	struct iov_iter *iter = data;
 	loff_t end = pos + length, done = 0;
 	ssize_t ret = 0;
 	int id;

 	if (iov_iter_rw(iter) == READ) {
 		end = min(end, i_size_read(inode));
 		if (pos >= end)
 			return 0;

 		if (iomap->type == IOMAP_HOLE || iomap->type == IOMAP_UNWRITTEN)
 			return iov_iter_zero(min(length, end - pos), iter);
 	}

 	if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
 		return -EIO;

 	/*
 	 * Write can allocate block for an area which has a hole page mapped
 	 * into page tables. We have to tear down these mappings so that data
 	 * written by write(2) is visible in mmap.
 	 */
 	if (iomap->flags & IOMAP_F_NEW) {
 		invalidate_inode_pages2_range(inode->i_mapping,
 					      pos >> PAGE_SHIFT,
 					      (end - 1) >> PAGE_SHIFT);
 	}

 	id = dax_read_lock();
 	while (pos < end) {
 		unsigned offset = pos & (PAGE_SIZE - 1);
 		const size_t size = ALIGN(length + offset, PAGE_SIZE);
 		const sector_t sector = dax_iomap_sector(iomap, pos);
 		ssize_t map_len;
 		pgoff_t pgoff;
 		void *kaddr;
 		pfn_t pfn;

 		if (fatal_signal_pending(current)) {
 			ret = -EINTR;
 			break;
 		}

 		ret = bdev_dax_pgoff(bdev, sector, size, &pgoff);
 		if (ret)
 			break;

 		map_len = dax_direct_access(dax_dev, pgoff, PHYS_PFN(size),
 				&kaddr, &pfn);
 		if (map_len < 0) {
 			ret = map_len;
 			break;
 		}

 		map_len = PFN_PHYS(map_len);
 		kaddr += offset;
 		map_len -= offset;
 		if (map_len > end - pos)
 			map_len = end - pos;

 		/*
 		 * The userspace address for the memory copy has already been
 		 * validated via access_ok() in either vfs_read() or
 		 * vfs_write(), depending on which operation we are doing.
 		 */
 		if (iov_iter_rw(iter) == WRITE)
 			map_len = dax_copy_from_iter(dax_dev, pgoff, kaddr,
 					map_len, iter);
 		else
 			map_len = copy_to_iter(kaddr, map_len, iter);
 		if (map_len <= 0) {
 			ret = map_len ? map_len : -EFAULT;
 			break;
 		}

 		pos += map_len;
 		length -= map_len;
 		done += map_len;
 	}
 	dax_read_unlock(id);

 	return done ? done : ret;
 }

 /**
  * dax_iomap_rw - Perform I/O to a DAX file
  * @iocb:	The control block for this I/O
  * @iter:	The addresses to do I/O from or to
  * @ops:	iomap ops passed from the file system
  *
  * This function performs read and write operations to directly mapped
  * persistent memory.  The callers needs to take care of read/write exclusion
  * and evicting any page cache pages in the region under I/O.
  */
 ssize_t
 dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
 		const struct iomap_ops *ops)
 {
 	struct address_space *mapping = iocb->ki_filp->f_mapping;
 	struct inode *inode = mapping->host;
 	loff_t pos = iocb->ki_pos, ret = 0, done = 0;
 	unsigned flags = 0;

 	if (iov_iter_rw(iter) == WRITE) {
 		lockdep_assert_held_exclusive(&inode->i_rwsem);
 		flags |= IOMAP_WRITE;
 	} else {
 		lockdep_assert_held(&inode->i_rwsem);
 	}

 	if (iocb->ki_flags & IOCB_NOWAIT)
 		flags |= IOMAP_NOWAIT;

 	while (iov_iter_count(iter)) {
 		ret = iomap_apply(inode, pos, iov_iter_count(iter), flags, ops,
 				iter, dax_iomap_actor);
 		if (ret <= 0)
 			break;
 		pos += ret;
 		done += ret;
 	}

 	iocb->ki_pos += done;
 	return done ? done : ret;
 }
 EXPORT_SYMBOL_GPL(dax_iomap_rw);

 static int dax_fault_return(int error)
 {
 	if (error == 0)
 		return VM_FAULT_NOPAGE;
 	if (error == -ENOMEM)
 		return VM_FAULT_OOM;
 	return VM_FAULT_SIGBUS;
 }

 static int dax_iomap_pte_fault(struct vm_fault *vmf,
 			       const struct iomap_ops *ops)
 {
 	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
 	struct inode *inode = mapping->host;
 	unsigned long vaddr = vmf->address;
 	loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;
 	sector_t sector;
 	struct iomap iomap = { 0 };
 	unsigned flags = IOMAP_FAULT;
 	int error, major = 0;
 	int vmf_ret = 0;
 	void *entry;

 	trace_dax_pte_fault(inode, vmf, vmf_ret);
 	/*
 	 * Check whether offset isn't beyond end of file now. Caller is supposed
 	 * to hold locks serializing us with truncate / punch hole so this is
 	 * a reliable test.
 	 */
 	if (pos >= i_size_read(inode)) {
 		vmf_ret = VM_FAULT_SIGBUS;
 		goto out;
 	}

 	if ((vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page)
 		flags |= IOMAP_WRITE;

 	entry = grab_mapping_entry(mapping, vmf->pgoff, 0);
 	if (IS_ERR(entry)) {
 		vmf_ret = dax_fault_return(PTR_ERR(entry));
 		goto out;
 	}

 	/*
 	 * It is possible, particularly with mixed reads & writes to private
 	 * mappings, that we have raced with a PMD fault that overlaps with
 	 * the PTE we need to set up.  If so just return and the fault will be
 	 * retried.
 	 */
 	if (pmd_trans_huge(*vmf->pmd) || pmd_devmap(*vmf->pmd)) {
 		vmf_ret = VM_FAULT_NOPAGE;
 		goto unlock_entry;
 	}

 	/*
 	 * Note that we don't bother to use iomap_apply here: DAX required
 	 * the file system block size to be equal the page size, which means
 	 * that we never have to deal with more than a single extent here.
 	 */
 	error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap);
 	if (error) {
 		vmf_ret = dax_fault_return(error);
 		goto unlock_entry;
 	}
 	if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) {
 		error = -EIO;	/* fs corruption? */
 		goto error_finish_iomap;
 	}

 	sector = dax_iomap_sector(&iomap, pos);

 	if (vmf->cow_page) {
 		switch (iomap.type) {
 		case IOMAP_HOLE:
 		case IOMAP_UNWRITTEN:
 			clear_user_highpage(vmf->cow_page, vaddr);
 			break;
 		case IOMAP_MAPPED:
 			error = copy_user_dax(iomap.bdev, iomap.dax_dev,
 					sector, PAGE_SIZE, vmf->cow_page, vaddr);
 			break;
 		default:
 			WARN_ON_ONCE(1);
 			error = -EIO;
 			break;
 		}

 		if (error)
 			goto error_finish_iomap;

 		__SetPageUptodate(vmf->cow_page);
 		vmf_ret = finish_fault(vmf);
 		if (!vmf_ret)
 			vmf_ret = VM_FAULT_DONE_COW;
 		goto finish_iomap;
 	}

 	switch (iomap.type) {
 	case IOMAP_MAPPED:
 		if (iomap.flags & IOMAP_F_NEW) {
 			count_vm_event(PGMAJFAULT);
 			count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
 			major = VM_FAULT_MAJOR;
 		}
 		error = dax_insert_mapping(mapping, iomap.bdev, iomap.dax_dev,
 				sector, PAGE_SIZE, entry, vmf->vma, vmf);
 		/* -EBUSY is fine, somebody else faulted on the same PTE */
 		if (error == -EBUSY)
 			error = 0;
 		break;
 	case IOMAP_UNWRITTEN:
 	case IOMAP_HOLE:
 		if (!(vmf->flags & FAULT_FLAG_WRITE)) {
 			vmf_ret = dax_load_hole(mapping, entry, vmf);
 			goto finish_iomap;
 		}
 		/*FALLTHRU*/
 	default:
 		WARN_ON_ONCE(1);
 		error = -EIO;
 		break;
 	}

  error_finish_iomap:
 	vmf_ret = dax_fault_return(error) | major;
  finish_iomap:
 	if (ops->iomap_end) {
 		int copied = PAGE_SIZE;

 		if (vmf_ret & VM_FAULT_ERROR)
 			copied = 0;
 		/*
 		 * The fault is done by now and there's no way back (other
 		 * thread may be already happily using PTE we have installed).
 		 * Just ignore error from ->iomap_end since we cannot do much
 		 * with it.
 		 */
 		ops->iomap_end(inode, pos, PAGE_SIZE, copied, flags, &iomap);
 	}
  unlock_entry:
 	put_locked_mapping_entry(mapping, vmf->pgoff);
  out:
 	trace_dax_pte_fault_done(inode, vmf, vmf_ret);
 	return vmf_ret;
 }

 #ifdef CONFIG_FS_DAX_PMD
 static int dax_pmd_insert_mapping(struct vm_fault *vmf, struct iomap *iomap,
 		loff_t pos, void *entry)
 {
 	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
 	const sector_t sector = dax_iomap_sector(iomap, pos);
 	struct dax_device *dax_dev = iomap->dax_dev;
 	struct block_device *bdev = iomap->bdev;
 	struct inode *inode = mapping->host;
 	const size_t size = PMD_SIZE;
 	void *ret = NULL, *kaddr;
 	long length = 0;
 	pgoff_t pgoff;
 	pfn_t pfn = {};
 	int id;

 	if (bdev_dax_pgoff(bdev, sector, size, &pgoff) != 0)
 		goto fallback;

 	id = dax_read_lock();
 	length = dax_direct_access(dax_dev, pgoff, PHYS_PFN(size), &kaddr, &pfn);
 	if (length < 0)
 		goto unlock_fallback;
 	length = PFN_PHYS(length);

 	if (length < size)
 		goto unlock_fallback;
 	if (pfn_t_to_pfn(pfn) & PG_PMD_COLOUR)
 		goto unlock_fallback;
 	if (!pfn_t_devmap(pfn))
 		goto unlock_fallback;
 	dax_read_unlock(id);

 	ret = dax_insert_mapping_entry(mapping, vmf, entry, sector,
 			RADIX_DAX_PMD);
 	if (IS_ERR(ret))
 		goto fallback;

 	trace_dax_pmd_insert_mapping(inode, vmf, length, pfn, ret);
 	return vmf_insert_pfn_pmd(vmf->vma, vmf->address, vmf->pmd,
 			pfn, vmf->flags & FAULT_FLAG_WRITE);

 unlock_fallback:
 	dax_read_unlock(id);
 fallback:
 	trace_dax_pmd_insert_mapping_fallback(inode, vmf, length, pfn, ret);
 	return VM_FAULT_FALLBACK;
 }

 static int dax_pmd_load_hole(struct vm_fault *vmf, struct iomap *iomap,
 		void *entry)
 {
 	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
 	unsigned long pmd_addr = vmf->address & PMD_MASK;
 	struct inode *inode = mapping->host;
 	struct page *zero_page;
 	void *ret = NULL;
 	spinlock_t *ptl;
 	pmd_t pmd_entry;

 	zero_page = mm_get_huge_zero_page(vmf->vma->vm_mm);

 	if (unlikely(!zero_page))
 		goto fallback;

 	ret = dax_insert_mapping_entry(mapping, vmf, entry, 0,
 			RADIX_DAX_PMD | RADIX_DAX_ZERO_PAGE);
 	if (IS_ERR(ret))
 		goto fallback;

 	ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
 	if (!pmd_none(*(vmf->pmd))) {
 		spin_unlock(ptl);
 		goto fallback;
 	}

 	pmd_entry = mk_pmd(zero_page, vmf->vma->vm_page_prot);
 	pmd_entry = pmd_mkhuge(pmd_entry);
 	set_pmd_at(vmf->vma->vm_mm, pmd_addr, vmf->pmd, pmd_entry);
 	spin_unlock(ptl);
 	trace_dax_pmd_load_hole(inode, vmf, zero_page, ret);
 	return VM_FAULT_NOPAGE;

 fallback:
 	trace_dax_pmd_load_hole_fallback(inode, vmf, zero_page, ret);
 	return VM_FAULT_FALLBACK;
 }

 static int dax_iomap_pmd_fault(struct vm_fault *vmf,
 			       const struct iomap_ops *ops)
 {
 	struct vm_area_struct *vma = vmf->vma;
 	struct address_space *mapping = vma->vm_file->f_mapping;
 	unsigned long pmd_addr = vmf->address & PMD_MASK;
 	bool write = vmf->flags & FAULT_FLAG_WRITE;
 	unsigned int iomap_flags = (write ? IOMAP_WRITE : 0) | IOMAP_FAULT;
 	struct inode *inode = mapping->host;
 	int result = VM_FAULT_FALLBACK;
 	struct iomap iomap = { 0 };
 	pgoff_t max_pgoff, pgoff;
 	void *entry;
 	loff_t pos;
 	int error;

 	/*
 	 * Check whether offset isn't beyond end of file now. Caller is
 	 * supposed to hold locks serializing us with truncate / punch hole so
 	 * this is a reliable test.
 	 */
 	pgoff = linear_page_index(vma, pmd_addr);
 	max_pgoff = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);

 	trace_dax_pmd_fault(inode, vmf, max_pgoff, 0);

 	/*
 	 * Make sure that the faulting address's PMD offset (color) matches
 	 * the PMD offset from the start of the file.  This is necessary so
 	 * that a PMD range in the page table overlaps exactly with a PMD
 	 * range in the radix tree.
 	 */
 	if ((vmf->pgoff & PG_PMD_COLOUR) !=
 	    ((vmf->address >> PAGE_SHIFT) & PG_PMD_COLOUR))
 		goto fallback;

 	/* Fall back to PTEs if we're going to COW */
 	if (write && !(vma->vm_flags & VM_SHARED))
 		goto fallback;

 	/* If the PMD would extend outside the VMA */
 	if (pmd_addr < vma->vm_start)
 		goto fallback;
 	if ((pmd_addr + PMD_SIZE) > vma->vm_end)
 		goto fallback;

 	if (pgoff >= max_pgoff) {
 		result = VM_FAULT_SIGBUS;
 		goto out;
 	}

 	/* If the PMD would extend beyond the file size */
 	if ((pgoff | PG_PMD_COLOUR) >= max_pgoff)
 		goto fallback;

 	/*
 	 * grab_mapping_entry() will make sure we get a 2MiB empty entry, a
 	 * 2MiB zero page entry or a DAX PMD.  If it can't (because a 4k page
 	 * is already in the tree, for instance), it will return -EEXIST and
 	 * we just fall back to 4k entries.
 	 */
 	entry = grab_mapping_entry(mapping, pgoff, RADIX_DAX_PMD);
 	if (IS_ERR(entry))
 		goto fallback;

 	/*
 	 * It is possible, particularly with mixed reads & writes to private
 	 * mappings, that we have raced with a PTE fault that overlaps with
 	 * the PMD we need to set up.  If so just return and the fault will be
 	 * retried.
 	 */
 	if (!pmd_none(*vmf->pmd) && !pmd_trans_huge(*vmf->pmd) &&
 			!pmd_devmap(*vmf->pmd)) {
 		result = 0;
 		goto unlock_entry;
 	}

 	/*
 	 * Note that we don't use iomap_apply here.  We aren't doing I/O, only
 	 * setting up a mapping, so really we're using iomap_begin() as a way
 	 * to look up our filesystem block.
 	 */
 	pos = (loff_t)pgoff << PAGE_SHIFT;
 	error = ops->iomap_begin(inode, pos, PMD_SIZE, iomap_flags, &iomap);
 	if (error)
 		goto unlock_entry;

 	if (iomap.offset + iomap.length < pos + PMD_SIZE)
 		goto finish_iomap;

 	switch (iomap.type) {
 	case IOMAP_MAPPED:
 		result = dax_pmd_insert_mapping(vmf, &iomap, pos, entry);
 		break;
 	case IOMAP_UNWRITTEN:
 	case IOMAP_HOLE:
 		if (WARN_ON_ONCE(write))
 			break;
 		result = dax_pmd_load_hole(vmf, &iomap, entry);
 		break;
 	default:
 		WARN_ON_ONCE(1);
 		break;
 	}

  finish_iomap:
 	if (ops->iomap_end) {
 		int copied = PMD_SIZE;

 		if (result == VM_FAULT_FALLBACK)
 			copied = 0;
 		/*
 		 * The fault is done by now and there's no way back (other
 		 * thread may be already happily using PMD we have installed).
 		 * Just ignore error from ->iomap_end since we cannot do much
 		 * with it.
 		 */
 		ops->iomap_end(inode, pos, PMD_SIZE, copied, iomap_flags,
 				&iomap);
 	}
  unlock_entry:
 	put_locked_mapping_entry(mapping, pgoff);
  fallback:
 	if (result == VM_FAULT_FALLBACK) {
 		split_huge_pmd(vma, vmf->pmd, vmf->address);
 		count_vm_event(THP_FAULT_FALLBACK);
 	}
 out:
 	trace_dax_pmd_fault_done(inode, vmf, max_pgoff, result);
 	return result;
 }
 #else
 static int dax_iomap_pmd_fault(struct vm_fault *vmf,
 			       const struct iomap_ops *ops)
 {
 	return VM_FAULT_FALLBACK;
 }
 #endif /* CONFIG_FS_DAX_PMD */

 /**
  * dax_iomap_fault - handle a page fault on a DAX file
  * @vmf: The description of the fault
  * @ops: iomap ops passed from the file system
  *
  * When a page fault occurs, filesystems may call this helper in
  * their fault handler for DAX files. dax_iomap_fault() assumes the caller
  * has done all the necessary locking for page fault to proceed
  * successfully.
  */
 int dax_iomap_fault(struct vm_fault *vmf, enum page_entry_size pe_size,
 		    const struct iomap_ops *ops)
 {
 	switch (pe_size) {
 	case PE_SIZE_PTE:
 		return dax_iomap_pte_fault(vmf, ops);
 	case PE_SIZE_PMD:
 		return dax_iomap_pmd_fault(vmf, ops);
 	default:
 		return VM_FAULT_FALLBACK;
 	}
 }
 EXPORT_SYMBOL_GPL(dax_iomap_fault);