Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1820 insertions, 0 deletions

diff --git a/fs/dax.c b/fs/dax.c
new file mode 100644
index 000000000..7451efc50
--- /dev/null
+++ b/fs/dax.c
@@ -0,0 +1,1820 @@
+/*
+ * 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)
+#define PG_PMD_NR	(PMD_SIZE >> PAGE_SHIFT)
+
+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_pfn(void *entry)
+{
+	return (unsigned long)entry >> RADIX_DAX_SHIFT;
+}
+
+static void *dax_radix_locked_entry(unsigned long pfn, unsigned long flags)
+{
+	return (void *)(RADIX_TREE_EXCEPTIONAL_ENTRY | flags |
+			(pfn << 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);
+}
+
+/*
+ * @entry may no longer be the entry at the index in the mapping.
+ * The important information it's conveying is whether the entry at
+ * this index used to be a PMD entry.
+ */
+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 the i_pages 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.  Must be called with the i_pages
+ * 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->i_pages.xa_lock);
+	return entry & RADIX_DAX_ENTRY_LOCK;
+}
+
+/*
+ * Mark the given slot as locked.  Must be called with the i_pages 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->i_pages.xa_lock);
+
+	entry |= RADIX_DAX_ENTRY_LOCK;
+	radix_tree_replace_slot(&mapping->i_pages, slot, (void *)entry);
+	return (void *)entry;
+}
+
+/*
+ * Mark the given slot as unlocked.  Must be called with the i_pages 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->i_pages.xa_lock);
+
+	entry &= ~(unsigned long)RADIX_DAX_ENTRY_LOCK;
+	radix_tree_replace_slot(&mapping->i_pages, slot, (void *)entry);
+	return (void *)entry;
+}
+
+static void put_unlocked_mapping_entry(struct address_space *mapping,
+				       pgoff_t index, 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.
+ *
+ * Must be called with the i_pages 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->i_pages, 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);
+		xa_unlock_irq(&mapping->i_pages);
+		schedule();
+		finish_wait(wq, &ewait.wait);
+		xa_lock_irq(&mapping->i_pages);
+	}
+}
+
+/*
+ * The only thing keeping the address space around is the i_pages lock
+ * (it's cycled in clear_inode() after removing the entries from i_pages)
+ * After we call xas_unlock_irq(), we cannot touch xas->xa.
+ */
+static void wait_entry_unlocked(struct address_space *mapping, pgoff_t index,
+		void ***slotp, void *entry)
+{
+	struct wait_exceptional_entry_queue ewait;
+	wait_queue_head_t *wq;
+
+	init_wait(&ewait.wait);
+	ewait.wait.func = wake_exceptional_entry_func;
+
+	wq = dax_entry_waitqueue(mapping, index, entry, &ewait.key);
+	/*
+	 * Unlike get_unlocked_entry() there is no guarantee that this
+	 * path ever successfully retrieves an unlocked entry before an
+	 * inode dies. Perform a non-exclusive wait in case this path
+	 * never successfully performs its own wake up.
+	 */
+	prepare_to_wait(wq, &ewait.wait, TASK_UNINTERRUPTIBLE);
+	xa_unlock_irq(&mapping->i_pages);
+	schedule();
+	finish_wait(wq, &ewait.wait);
+}
+
+static void unlock_mapping_entry(struct address_space *mapping, pgoff_t index)
+{
+	void *entry, **slot;
+
+	xa_lock_irq(&mapping->i_pages);
+	entry = __radix_tree_lookup(&mapping->i_pages, index, NULL, &slot);
+	if (WARN_ON_ONCE(!entry || !radix_tree_exceptional_entry(entry) ||
+			 !slot_locked(mapping, slot))) {
+		xa_unlock_irq(&mapping->i_pages);
+		return;
+	}
+	unlock_slot(mapping, slot);
+	xa_unlock_irq(&mapping->i_pages);
+	dax_wake_mapping_entry_waiter(mapping, index, entry, false);
+}
+
+static void put_locked_mapping_entry(struct address_space *mapping,
+		pgoff_t index)
+{
+	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);
+}
+
+static unsigned long dax_entry_size(void *entry)
+{
+	if (dax_is_zero_entry(entry))
+		return 0;
+	else if (dax_is_empty_entry(entry))
+		return 0;
+	else if (dax_is_pmd_entry(entry))
+		return PMD_SIZE;
+	else
+		return PAGE_SIZE;
+}
+
+static unsigned long dax_radix_end_pfn(void *entry)
+{
+	return dax_radix_pfn(entry) + dax_entry_size(entry) / PAGE_SIZE;
+}
+
+/*
+ * Iterate through all mapped pfns represented by an entry, i.e. skip
+ * 'empty' and 'zero' entries.
+ */
+#define for_each_mapped_pfn(entry, pfn) \
+	for (pfn = dax_radix_pfn(entry); \
+			pfn < dax_radix_end_pfn(entry); pfn++)
+
+/*
+ * TODO: for reflink+dax we need a way to associate a single page with
+ * multiple address_space instances at different linear_page_index()
+ * offsets.
+ */
+static void dax_associate_entry(void *entry, struct address_space *mapping,
+		struct vm_area_struct *vma, unsigned long address)
+{
+	unsigned long size = dax_entry_size(entry), pfn, index;
+	int i = 0;
+
+	if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
+		return;
+
+	index = linear_page_index(vma, address & ~(size - 1));
+	for_each_mapped_pfn(entry, pfn) {
+		struct page *page = pfn_to_page(pfn);
+
+		WARN_ON_ONCE(page->mapping);
+		page->mapping = mapping;
+		page->index = index + i++;
+	}
+}
+
+static void dax_disassociate_entry(void *entry, struct address_space *mapping,
+		bool trunc)
+{
+	unsigned long pfn;
+
+	if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
+		return;
+
+	for_each_mapped_pfn(entry, pfn) {
+		struct page *page = pfn_to_page(pfn);
+
+		WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
+		WARN_ON_ONCE(page->mapping && page->mapping != mapping);
+		page->mapping = NULL;
+		page->index = 0;
+	}
+}
+
+static struct page *dax_busy_page(void *entry)
+{
+	unsigned long pfn;
+
+	for_each_mapped_pfn(entry, pfn) {
+		struct page *page = pfn_to_page(pfn);
+
+		if (page_ref_count(page) > 1)
+			return page;
+	}
+	return NULL;
+}
+
+bool dax_lock_mapping_entry(struct page *page)
+{
+	pgoff_t index;
+	struct inode *inode;
+	bool did_lock = false;
+	void *entry = NULL, **slot;
+	struct address_space *mapping;
+
+	rcu_read_lock();
+	for (;;) {
+		mapping = READ_ONCE(page->mapping);
+
+		if (!mapping || !dax_mapping(mapping))
+			break;
+
+		/*
+		 * In the device-dax case there's no need to lock, a
+		 * struct dev_pagemap pin is sufficient to keep the
+		 * inode alive, and we assume we have dev_pagemap pin
+		 * otherwise we would not have a valid pfn_to_page()
+		 * translation.
+		 */
+		inode = mapping->host;
+		if (S_ISCHR(inode->i_mode)) {
+			did_lock = true;
+			break;
+		}
+
+		xa_lock_irq(&mapping->i_pages);
+		if (mapping != page->mapping) {
+			xa_unlock_irq(&mapping->i_pages);
+			continue;
+		}
+		index = page->index;
+
+		entry = __radix_tree_lookup(&mapping->i_pages, index,
+						NULL, &slot);
+		if (!entry) {
+			xa_unlock_irq(&mapping->i_pages);
+			break;
+		} else if (slot_locked(mapping, slot)) {
+			rcu_read_unlock();
+			wait_entry_unlocked(mapping, index, &slot, entry);
+			rcu_read_lock();
+			continue;
+		}
+		lock_slot(mapping, slot);
+		did_lock = true;
+		xa_unlock_irq(&mapping->i_pages);
+		break;
+	}
+	rcu_read_unlock();
+
+	return did_lock;
+}
+
+void dax_unlock_mapping_entry(struct page *page)
+{
+	struct address_space *mapping = page->mapping;
+	struct inode *inode = mapping->host;
+
+	if (S_ISCHR(inode->i_mode))
+		return;
+
+	unlock_mapping_entry(mapping, page->index);
+}
+
+/*
+ * 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:
+	xa_lock_irq(&mapping->i_pages);
+	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
+			 * the i_pages lock.
+			 */
+			entry = lock_slot(mapping, slot);
+		}
+
+		xa_unlock_irq(&mapping->i_pages);
+		/*
+		 * 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_pages(mapping, index & ~PG_PMD_COLOUR,
+							PG_PMD_NR, false);
+
+		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);
+		}
+		xa_lock_irq(&mapping->i_pages);
+
+		if (!entry) {
+			/*
+			 * We needed to drop the i_pages 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->i_pages, index,
+					NULL, &slot);
+			if (entry) {
+				radix_tree_preload_end();
+				xa_unlock_irq(&mapping->i_pages);
+				goto restart;
+			}
+		}
+
+		if (pmd_downgrade) {
+			dax_disassociate_entry(entry, mapping, false);
+			radix_tree_delete(&mapping->i_pages, 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->i_pages, index,
+				dax_radix_order(entry), entry);
+		radix_tree_preload_end();
+		if (err) {
+			xa_unlock_irq(&mapping->i_pages);
+			/*
+			 * 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++;
+		xa_unlock_irq(&mapping->i_pages);
+		return entry;
+	}
+	entry = lock_slot(mapping, slot);
+ out_unlock:
+	xa_unlock_irq(&mapping->i_pages);
+	return entry;
+}
+
+/**
+ * dax_layout_busy_page - find first pinned page in @mapping
+ * @mapping: address space to scan for a page with ref count > 1
+ *
+ * DAX requires ZONE_DEVICE mapped pages. These pages are never
+ * 'onlined' to the page allocator so they are considered idle when
+ * page->count == 1. A filesystem uses this interface to determine if
+ * any page in the mapping is busy, i.e. for DMA, or other
+ * get_user_pages() usages.
+ *
+ * It is expected that the filesystem is holding locks to block the
+ * establishment of new mappings in this address_space. I.e. it expects
+ * to be able to run unmap_mapping_range() and subsequently not race
+ * mapping_mapped() becoming true.
+ */
+struct page *dax_layout_busy_page(struct address_space *mapping)
+{
+	pgoff_t	indices[PAGEVEC_SIZE];
+	struct page *page = NULL;
+	struct pagevec pvec;
+	pgoff_t	index, end;
+	unsigned i;
+
+	/*
+	 * In the 'limited' case get_user_pages() for dax is disabled.
+	 */
+	if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
+		return NULL;
+
+	if (!dax_mapping(mapping) || !mapping_mapped(mapping))
+		return NULL;
+
+	pagevec_init(&pvec);
+	index = 0;
+	end = -1;
+
+	/*
+	 * If we race get_user_pages_fast() here either we'll see the
+	 * elevated page count in the pagevec_lookup and wait, or
+	 * get_user_pages_fast() will see that the page it took a reference
+	 * against is no longer mapped in the page tables and bail to the
+	 * get_user_pages() slow path.  The slow path is protected by
+	 * pte_lock() and pmd_lock(). New references are not taken without
+	 * holding those locks, and unmap_mapping_range() will not zero the
+	 * pte or pmd without holding the respective lock, so we are
+	 * guaranteed to either see new references or prevent new
+	 * references from being established.
+	 */
+	unmap_mapping_range(mapping, 0, 0, 0);
+
+	while (index < end && pagevec_lookup_entries(&pvec, mapping, index,
+				min(end - index, (pgoff_t)PAGEVEC_SIZE),
+				indices)) {
+		pgoff_t nr_pages = 1;
+
+		for (i = 0; i < pagevec_count(&pvec); i++) {
+			struct page *pvec_ent = pvec.pages[i];
+			void *entry;
+
+			index = indices[i];
+			if (index >= end)
+				break;
+
+			if (WARN_ON_ONCE(
+			     !radix_tree_exceptional_entry(pvec_ent)))
+				continue;
+
+			xa_lock_irq(&mapping->i_pages);
+			entry = get_unlocked_mapping_entry(mapping, index, NULL);
+			if (entry) {
+				page = dax_busy_page(entry);
+				/*
+				 * Account for multi-order entries at
+				 * the end of the pagevec.
+				 */
+				if (i + 1 >= pagevec_count(&pvec))
+					nr_pages = 1UL << dax_radix_order(entry);
+			}
+			put_unlocked_mapping_entry(mapping, index, entry);
+			xa_unlock_irq(&mapping->i_pages);
+			if (page)
+				break;
+		}
+
+		/*
+		 * We don't expect normal struct page entries to exist in our
+		 * tree, but we keep these pagevec calls so that this code is
+		 * consistent with the common pattern for handling pagevecs
+		 * throughout the kernel.
+		 */
+		pagevec_remove_exceptionals(&pvec);
+		pagevec_release(&pvec);
+		index += nr_pages;
+
+		if (page)
+			break;
+	}
+	return page;
+}
+EXPORT_SYMBOL_GPL(dax_layout_busy_page);
+
+static int __dax_invalidate_mapping_entry(struct address_space *mapping,
+					  pgoff_t index, bool trunc)
+{
+	int ret = 0;
+	void *entry;
+	struct radix_tree_root *pages = &mapping->i_pages;
+
+	xa_lock_irq(pages);
+	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(pages, index, PAGECACHE_TAG_DIRTY) ||
+	     radix_tree_tag_get(pages, index, PAGECACHE_TAG_TOWRITE)))
+		goto out;
+	dax_disassociate_entry(entry, mapping, trunc);
+	radix_tree_delete(pages, index);
+	mapping->nrexceptional--;
+	ret = 1;
+out:
+	put_unlocked_mapping_entry(mapping, index, entry);
+	xa_unlock_irq(pages);
+	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;
+	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, NULL);
+	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, pfn_t pfn_t,
+				      unsigned long flags, bool dirty)
+{
+	struct radix_tree_root *pages = &mapping->i_pages;
+	unsigned long pfn = pfn_t_to_pfn(pfn_t);
+	pgoff_t index = vmf->pgoff;
+	void *new_entry;
+
+	if (dirty)
+		__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_pages(mapping, index & ~PG_PMD_COLOUR,
+							PG_PMD_NR, false);
+		else /* pte entry */
+			unmap_mapping_pages(mapping, vmf->pgoff, 1, false);
+	}
+
+	xa_lock_irq(pages);
+	new_entry = dax_radix_locked_entry(pfn, flags);
+	if (dax_entry_size(entry) != dax_entry_size(new_entry)) {
+		dax_disassociate_entry(entry, mapping, false);
+		dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address);
+	}
+
+	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(pages, index, &node, &slot);
+		WARN_ON_ONCE(ret != entry);
+		__radix_tree_replace(pages, node, slot,
+				     new_entry, NULL);
+		entry = new_entry;
+	}
+
+	if (dirty)
+		radix_tree_tag_set(pages, index, PAGECACHE_TAG_DIRTY);
+
+	xa_unlock_irq(pages);
+	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;
+
+		/*
+		 * No need to call mmu_notifier_invalidate_range() as we are
+		 * downgrading page table protection not changing it to point
+		 * to a new page.
+		 *
+		 * See Documentation/vm/mmu_notifier.rst
+		 */
+		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_range(vma, address,
+					  address + HPAGE_PMD_SIZE);
+			pmd = pmdp_invalidate(vma, address, pmdp);
+			pmd = pmd_wrprotect(pmd);
+			pmd = pmd_mkclean(pmd);
+			set_pmd_at(vma->vm_mm, address, pmdp, pmd);
+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);
+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 dax_device *dax_dev,
+		struct address_space *mapping, pgoff_t index, void *entry)
+{
+	struct radix_tree_root *pages = &mapping->i_pages;
+	void *entry2, **slot;
+	unsigned long pfn;
+	long ret = 0;
+	size_t size;
+
+	/*
+	 * A page got tagged dirty in DAX mapping? Something is seriously
+	 * wrong.
+	 */
+	if (WARN_ON(!radix_tree_exceptional_entry(entry)))
+		return -EIO;
+
+	xa_lock_irq(pages);
+	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 pfns as we must not bail out due to difference in lockbit
+	 * or entry type.
+	 */
+	if (dax_radix_pfn(entry2) != dax_radix_pfn(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(pages, 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 the i_pages lock and once they do that
+	 * they will see the entry locked and wait for it to unlock.
+	 */
+	radix_tree_tag_clear(pages, index, PAGECACHE_TAG_TOWRITE);
+	xa_unlock_irq(pages);
+
+	/*
+	 * 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 pfn we pull from 'entry'.
+	 * This allows us to flush for PMD_SIZE and not have to worry about
+	 * partial PMD writebacks.
+	 */
+	pfn = dax_radix_pfn(entry);
+	size = PAGE_SIZE << dax_radix_order(entry);
+
+	dax_mapping_entry_mkclean(mapping, index, pfn);
+	dax_flush(dax_dev, page_address(pfn_to_page(pfn)), 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.
+	 */
+	xa_lock_irq(pages);
+	radix_tree_tag_clear(pages, index, PAGECACHE_TAG_DIRTY);
+	xa_unlock_irq(pages);
+	trace_dax_writeback_one(mapping->host, index, size >> PAGE_SHIFT);
+	put_locked_mapping_entry(mapping, index);
+	return ret;
+
+ put_unlocked:
+	put_unlocked_mapping_entry(mapping, index, entry2);
+	xa_unlock_irq(pages);
+	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);
+	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(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 sector_t dax_iomap_sector(struct iomap *iomap, loff_t pos)
+{
+	return (iomap->addr + (pos & PAGE_MASK) - iomap->offset) >> 9;
+}
+
+static int dax_iomap_pfn(struct iomap *iomap, loff_t pos, size_t size,
+			 pfn_t *pfnp)
+{
+	const sector_t sector = dax_iomap_sector(iomap, pos);
+	pgoff_t pgoff;
+	int id, rc;
+	long length;
+
+	rc = bdev_dax_pgoff(iomap->bdev, sector, size, &pgoff);
+	if (rc)
+		return rc;
+	id = dax_read_lock();
+	length = dax_direct_access(iomap->dax_dev, pgoff, PHYS_PFN(size),
+				   NULL, pfnp);
+	if (length < 0) {
+		rc = length;
+		goto out;
+	}
+	rc = -EINVAL;
+	if (PFN_PHYS(length) < size)
+		goto out;
+	if (pfn_t_to_pfn(*pfnp) & (PHYS_PFN(size)-1))
+		goto out;
+	/* For larger pages we need devmap */
+	if (length > 1 && !pfn_t_devmap(*pfnp))
+		goto out;
+	rc = 0;
+out:
+	dax_read_unlock(id);
+	return rc;
+}
+
+/*
+ * 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 vm_fault_t dax_load_hole(struct address_space *mapping, void *entry,
+			 struct vm_fault *vmf)
+{
+	struct inode *inode = mapping->host;
+	unsigned long vaddr = vmf->address;
+	pfn_t pfn = pfn_to_pfn_t(my_zero_pfn(vaddr));
+	vm_fault_t ret;
+
+	dax_insert_mapping_entry(mapping, vmf, entry, pfn, RADIX_DAX_ZERO_PAGE,
+			false);
+	ret = vmf_insert_mixed(vmf->vma, vaddr, pfn);
+	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;
+
+		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, NULL);
+		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 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;
+	size_t xfer;
+	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;
+
+		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, NULL);
+		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)
+			xfer = dax_copy_from_iter(dax_dev, pgoff, kaddr,
+					map_len, iter);
+		else
+			xfer = dax_copy_to_iter(dax_dev, pgoff, kaddr,
+					map_len, iter);
+
+		pos += xfer;
+		length -= xfer;
+		done += xfer;
+
+		if (xfer == 0)
+			ret = -EFAULT;
+		if (xfer < map_len)
+			break;
+	}
+	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 vm_fault_t dax_fault_return(int error)
+{
+	if (error == 0)
+		return VM_FAULT_NOPAGE;
+	if (error == -ENOMEM)
+		return VM_FAULT_OOM;
+	return VM_FAULT_SIGBUS;
+}
+
+/*
+ * MAP_SYNC on a dax mapping guarantees dirty metadata is
+ * flushed on write-faults (non-cow), but not read-faults.
+ */
+static bool dax_fault_is_synchronous(unsigned long flags,
+		struct vm_area_struct *vma, struct iomap *iomap)
+{
+	return (flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC)
+		&& (iomap->flags & IOMAP_F_DIRTY);
+}
+
+static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
+			       int *iomap_errp, const struct iomap_ops *ops)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct address_space *mapping = vma->vm_file->f_mapping;
+	struct inode *inode = mapping->host;
+	unsigned long vaddr = vmf->address;
+	loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;
+	struct iomap iomap = { 0 };
+	unsigned flags = IOMAP_FAULT;
+	int error, major = 0;
+	bool write = vmf->flags & FAULT_FLAG_WRITE;
+	bool sync;
+	vm_fault_t ret = 0;
+	void *entry;
+	pfn_t pfn;
+
+	trace_dax_pte_fault(inode, 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)) {
+		ret = VM_FAULT_SIGBUS;
+		goto out;
+	}
+
+	if (write && !vmf->cow_page)
+		flags |= IOMAP_WRITE;
+
+	entry = grab_mapping_entry(mapping, vmf->pgoff, 0);
+	if (IS_ERR(entry)) {
+		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)) {
+		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 (iomap_errp)
+		*iomap_errp = error;
+	if (error) {
+		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;
+	}
+
+	if (vmf->cow_page) {
+		sector_t sector = dax_iomap_sector(&iomap, pos);
+
+		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);
+		ret = finish_fault(vmf);
+		if (!ret)
+			ret = VM_FAULT_DONE_COW;
+		goto finish_iomap;
+	}
+
+	sync = dax_fault_is_synchronous(flags, vma, &iomap);
+
+	switch (iomap.type) {
+	case IOMAP_MAPPED:
+		if (iomap.flags & IOMAP_F_NEW) {
+			count_vm_event(PGMAJFAULT);
+			count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
+			major = VM_FAULT_MAJOR;
+		}
+		error = dax_iomap_pfn(&iomap, pos, PAGE_SIZE, &pfn);
+		if (error < 0)
+			goto error_finish_iomap;
+
+		entry = dax_insert_mapping_entry(mapping, vmf, entry, pfn,
+						 0, write && !sync);
+
+		/*
+		 * If we are doing synchronous page fault and inode needs fsync,
+		 * we can insert PTE into page tables only after that happens.
+		 * Skip insertion for now and return the pfn so that caller can
+		 * insert it after fsync is done.
+		 */
+		if (sync) {
+			if (WARN_ON_ONCE(!pfnp)) {
+				error = -EIO;
+				goto error_finish_iomap;
+			}
+			*pfnp = pfn;
+			ret = VM_FAULT_NEEDDSYNC | major;
+			goto finish_iomap;
+		}
+		trace_dax_insert_mapping(inode, vmf, entry);
+		if (write)
+			ret = vmf_insert_mixed_mkwrite(vma, vaddr, pfn);
+		else
+			ret = vmf_insert_mixed(vma, vaddr, pfn);
+
+		goto finish_iomap;
+	case IOMAP_UNWRITTEN:
+	case IOMAP_HOLE:
+		if (!write) {
+			ret = dax_load_hole(mapping, entry, vmf);
+			goto finish_iomap;
+		}
+		/*FALLTHRU*/
+	default:
+		WARN_ON_ONCE(1);
+		error = -EIO;
+		break;
+	}
+
+ error_finish_iomap:
+	ret = dax_fault_return(error);
+ finish_iomap:
+	if (ops->iomap_end) {
+		int copied = PAGE_SIZE;
+
+		if (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, ret);
+	return ret | major;
+}
+
+#ifdef CONFIG_FS_DAX_PMD
+static vm_fault_t 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;
+	pfn_t pfn;
+
+	zero_page = mm_get_huge_zero_page(vmf->vma->vm_mm);
+
+	if (unlikely(!zero_page))
+		goto fallback;
+
+	pfn = page_to_pfn_t(zero_page);
+	ret = dax_insert_mapping_entry(mapping, vmf, entry, pfn,
+			RADIX_DAX_PMD | RADIX_DAX_ZERO_PAGE, false);
+
+	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 vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
+			       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;
+	bool sync;
+	unsigned int iomap_flags = (write ? IOMAP_WRITE : 0) | IOMAP_FAULT;
+	struct inode *inode = mapping->host;
+	vm_fault_t result = VM_FAULT_FALLBACK;
+	struct iomap iomap = { 0 };
+	pgoff_t max_pgoff, pgoff;
+	void *entry;
+	loff_t pos;
+	int error;
+	pfn_t pfn;
+
+	/*
+	 * 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;
+
+	sync = dax_fault_is_synchronous(iomap_flags, vma, &iomap);
+
+	switch (iomap.type) {
+	case IOMAP_MAPPED:
+		error = dax_iomap_pfn(&iomap, pos, PMD_SIZE, &pfn);
+		if (error < 0)
+			goto finish_iomap;
+
+		entry = dax_insert_mapping_entry(mapping, vmf, entry, pfn,
+						RADIX_DAX_PMD, write && !sync);
+
+		/*
+		 * If we are doing synchronous page fault and inode needs fsync,
+		 * we can insert PMD into page tables only after that happens.
+		 * Skip insertion for now and return the pfn so that caller can
+		 * insert it after fsync is done.
+		 */
+		if (sync) {
+			if (WARN_ON_ONCE(!pfnp))
+				goto finish_iomap;
+			*pfnp = pfn;
+			result = VM_FAULT_NEEDDSYNC;
+			goto finish_iomap;
+		}
+
+		trace_dax_pmd_insert_mapping(inode, vmf, PMD_SIZE, pfn, entry);
+		result = vmf_insert_pfn_pmd(vmf, pfn, write);
+		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 vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
+			       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
+ * @pe_size: Size of the page to fault in
+ * @pfnp: PFN to insert for synchronous faults if fsync is required
+ * @iomap_errp: Storage for detailed error code in case of error
+ * @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.
+ */
+vm_fault_t dax_iomap_fault(struct vm_fault *vmf, enum page_entry_size pe_size,
+		    pfn_t *pfnp, int *iomap_errp, const struct iomap_ops *ops)
+{
+	switch (pe_size) {
+	case PE_SIZE_PTE:
+		return dax_iomap_pte_fault(vmf, pfnp, iomap_errp, ops);
+	case PE_SIZE_PMD:
+		return dax_iomap_pmd_fault(vmf, pfnp, ops);
+	default:
+		return VM_FAULT_FALLBACK;
+	}
+}
+EXPORT_SYMBOL_GPL(dax_iomap_fault);
+
+/**
+ * dax_insert_pfn_mkwrite - insert PTE or PMD entry into page tables
+ * @vmf: The description of the fault
+ * @pe_size: Size of entry to be inserted
+ * @pfn: PFN to insert
+ *
+ * This function inserts writeable PTE or PMD entry into page tables for mmaped
+ * DAX file.  It takes care of marking corresponding radix tree entry as dirty
+ * as well.
+ */
+static vm_fault_t dax_insert_pfn_mkwrite(struct vm_fault *vmf,
+				  enum page_entry_size pe_size,
+				  pfn_t pfn)
+{
+	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
+	void *entry, **slot;
+	pgoff_t index = vmf->pgoff;
+	vm_fault_t ret;
+
+	xa_lock_irq(&mapping->i_pages);
+	entry = get_unlocked_mapping_entry(mapping, index, &slot);
+	/* Did we race with someone splitting entry or so? */
+	if (!entry ||
+	    (pe_size == PE_SIZE_PTE && !dax_is_pte_entry(entry)) ||
+	    (pe_size == PE_SIZE_PMD && !dax_is_pmd_entry(entry))) {
+		put_unlocked_mapping_entry(mapping, index, entry);
+		xa_unlock_irq(&mapping->i_pages);
+		trace_dax_insert_pfn_mkwrite_no_entry(mapping->host, vmf,
+						      VM_FAULT_NOPAGE);
+		return VM_FAULT_NOPAGE;
+	}
+	radix_tree_tag_set(&mapping->i_pages, index, PAGECACHE_TAG_DIRTY);
+	entry = lock_slot(mapping, slot);
+	xa_unlock_irq(&mapping->i_pages);
+	switch (pe_size) {
+	case PE_SIZE_PTE:
+		ret = vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
+		break;
+#ifdef CONFIG_FS_DAX_PMD
+	case PE_SIZE_PMD:
+		ret = vmf_insert_pfn_pmd(vmf, pfn, FAULT_FLAG_WRITE);
+		break;
+#endif
+	default:
+		ret = VM_FAULT_FALLBACK;
+	}
+	put_locked_mapping_entry(mapping, index);
+	trace_dax_insert_pfn_mkwrite(mapping->host, vmf, ret);
+	return ret;
+}
+
+/**
+ * dax_finish_sync_fault - finish synchronous page fault
+ * @vmf: The description of the fault
+ * @pe_size: Size of entry to be inserted
+ * @pfn: PFN to insert
+ *
+ * This function ensures that the file range touched by the page fault is
+ * stored persistently on the media and handles inserting of appropriate page
+ * table entry.
+ */
+vm_fault_t dax_finish_sync_fault(struct vm_fault *vmf,
+		enum page_entry_size pe_size, pfn_t pfn)
+{
+	int err;
+	loff_t start = ((loff_t)vmf->pgoff) << PAGE_SHIFT;
+	size_t len = 0;
+
+	if (pe_size == PE_SIZE_PTE)
+		len = PAGE_SIZE;
+	else if (pe_size == PE_SIZE_PMD)
+		len = PMD_SIZE;
+	else
+		WARN_ON_ONCE(1);
+	err = vfs_fsync_range(vmf->vma->vm_file, start, start + len - 1, 1);
+	if (err)
+		return VM_FAULT_SIGBUS;
+	return dax_insert_pfn_mkwrite(vmf, pe_size, pfn);
+}
+EXPORT_SYMBOL_GPL(dax_finish_sync_fault);