// SPDX-License-Identifier: GPL-2.0-only

  /*
   * 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>

   */
  
  #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 <asm/pgalloc.h>

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

  static inline unsigned int pe_order(enum page_entry_size pe_size)
  {
  	if (pe_size == PE_SIZE_PTE)
  		return PAGE_SHIFT - PAGE_SHIFT;
  	if (pe_size == PE_SIZE_PMD)
  		return PMD_SHIFT - PAGE_SHIFT;
  	if (pe_size == PE_SIZE_PUD)
  		return PUD_SHIFT - PAGE_SHIFT;
  	return ~0;
  }

  /* 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)

  /* The order of a PMD entry */
  #define PMD_ORDER	(PMD_SHIFT - 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);

  /*

   * DAX pagecache entries use XArray value entries so they can't be mistaken
   * for pages.  We use one bit 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 DAX_SHIFT	(4)
  #define DAX_LOCKED	(1UL << 0)
  #define DAX_PMD		(1UL << 1)
  #define DAX_ZERO_PAGE	(1UL << 2)
  #define DAX_EMPTY	(1UL << 3)

  static unsigned long dax_to_pfn(void *entry)

  {

  	return xa_to_value(entry) >> DAX_SHIFT;

  }

  static void *dax_make_entry(pfn_t pfn, unsigned long flags)
  {
  	return xa_mk_value(flags | (pfn_t_to_pfn(pfn) << DAX_SHIFT));
  }

  static bool dax_is_locked(void *entry)
  {
  	return xa_to_value(entry) & DAX_LOCKED;
  }

  static unsigned int dax_entry_order(void *entry)

  {

  	if (xa_to_value(entry) & DAX_PMD)

  		return PMD_ORDER;

  	return 0;
  }

  static unsigned long dax_is_pmd_entry(void *entry)

  {

  	return xa_to_value(entry) & DAX_PMD;

  }

  static bool dax_is_pte_entry(void *entry)

  {

  	return !(xa_to_value(entry) & DAX_PMD);

  }

  static int dax_is_zero_entry(void *entry)

  {

  	return xa_to_value(entry) & DAX_ZERO_PAGE;

  }

  static int dax_is_empty_entry(void *entry)

  {

  	return xa_to_value(entry) & DAX_EMPTY;

  }

  /*

   * true if the entry that was found is of a smaller order than the entry
   * we were looking for
   */
  static bool dax_is_conflict(void *entry)
  {
  	return entry == XA_RETRY_ENTRY;
  }
  
  /*

   * DAX page cache entry locking

   */
  struct exceptional_entry_key {

  	struct xarray *xa;

  	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 xa_state *xas,
  		void *entry, struct exceptional_entry_key *key)

  {
  	unsigned long hash;

  	unsigned long index = xas->xa_index;

  
  	/*
  	 * 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->xa = xas->xa;

  	key->entry_start = index;

  	hash = hash_long((unsigned long)xas->xa ^ 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->xa != ewait->key.xa ||

  	    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_entry(struct xa_state *xas, void *entry, bool wake_all)

  {
  	struct exceptional_entry_key key;
  	wait_queue_head_t *wq;

  	wq = dax_entry_waitqueue(xas, 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);
  }

  /*
   * Look up entry in page cache, wait for it to become unlocked if it
   * is a DAX entry and return it.  The caller must subsequently call
   * put_unlocked_entry() if it did not lock the entry or dax_unlock_entry()

   * if it did.  The entry returned may have a larger order than @order.
   * If @order is larger than the order of the entry found in i_pages, this
   * function returns a dax_is_conflict entry.

   *
   * Must be called with the i_pages lock held.
   */

  static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)

  {
  	void *entry;
  	struct wait_exceptional_entry_queue ewait;
  	wait_queue_head_t *wq;
  
  	init_wait(&ewait.wait);
  	ewait.wait.func = wake_exceptional_entry_func;
  
  	for (;;) {

  		entry = xas_find_conflict(xas);

  		if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
  			return entry;

  		if (dax_entry_order(entry) < order)
  			return XA_RETRY_ENTRY;

  		if (!dax_is_locked(entry))

  			return entry;

  		wq = dax_entry_waitqueue(xas, entry, &ewait.key);

  		prepare_to_wait_exclusive(wq, &ewait.wait,
  					  TASK_UNINTERRUPTIBLE);
  		xas_unlock_irq(xas);
  		xas_reset(xas);
  		schedule();
  		finish_wait(wq, &ewait.wait);
  		xas_lock_irq(xas);
  	}
  }

  /*
   * 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 xa_state *xas, 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(xas, 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);

  	xas_unlock_irq(xas);
  	schedule();
  	finish_wait(wq, &ewait.wait);

  }

  static void put_unlocked_entry(struct xa_state *xas, void *entry)
  {
  	/* If we were the only waiter woken, wake the next one */

  	if (entry && !dax_is_conflict(entry))

  		dax_wake_entry(xas, entry, false);
  }
  
  /*
   * We used the xa_state to get the entry, but then we locked the entry and
   * dropped the xa_lock, so we know the xa_state is stale and must be reset
   * before use.
   */
  static void dax_unlock_entry(struct xa_state *xas, void *entry)
  {
  	void *old;

  	BUG_ON(dax_is_locked(entry));

  	xas_reset(xas);
  	xas_lock_irq(xas);
  	old = xas_store(xas, entry);
  	xas_unlock_irq(xas);
  	BUG_ON(!dax_is_locked(old));
  	dax_wake_entry(xas, entry, false);
  }
  
  /*
   * Return: The entry stored at this location before it was locked.
   */
  static void *dax_lock_entry(struct xa_state *xas, void *entry)
  {
  	unsigned long v = xa_to_value(entry);
  	return xas_store(xas, xa_mk_value(v | DAX_LOCKED));
  }

  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_end_pfn(void *entry)

  {

  	return dax_to_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_to_pfn(entry); \
  			pfn < dax_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;
  }

  /*
   * dax_lock_mapping_entry - Lock the DAX entry corresponding to a page
   * @page: The page whose entry we want to lock
   *
   * Context: Process context.

   * Return: A cookie to pass to dax_unlock_page() or 0 if the entry could
   * not be locked.

   */

  dax_entry_t dax_lock_page(struct page *page)

  {

  	XA_STATE(xas, NULL, 0);
  	void *entry;

  	/* Ensure page->mapping isn't freed while we look at it */
  	rcu_read_lock();

  	for (;;) {

  		struct address_space *mapping = READ_ONCE(page->mapping);

  		entry = NULL;

  		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.
  		 */

  		entry = (void *)~0UL;

  		if (S_ISCHR(mapping->host->i_mode))

  			break;

  		xas.xa = &mapping->i_pages;
  		xas_lock_irq(&xas);

  		if (mapping != page->mapping) {

  			xas_unlock_irq(&xas);

  			continue;
  		}

  		xas_set(&xas, page->index);
  		entry = xas_load(&xas);
  		if (dax_is_locked(entry)) {

  			rcu_read_unlock();

  			wait_entry_unlocked(&xas, entry);

  			rcu_read_lock();

  			continue;

  		}

  		dax_lock_entry(&xas, entry);
  		xas_unlock_irq(&xas);

  		break;

  	}

  	rcu_read_unlock();

  	return (dax_entry_t)entry;

  }

  void dax_unlock_page(struct page *page, dax_entry_t cookie)

  {
  	struct address_space *mapping = page->mapping;

  	XA_STATE(xas, &mapping->i_pages, page->index);

  	if (S_ISCHR(mapping->host->i_mode))

  		return;

  	dax_unlock_entry(&xas, (void *)cookie);

  }

  /*

   * Find page cache entry at given index. If it is a DAX entry, return it
   * with the entry locked. If the page cache doesn't contain an entry at
   * that index, add a locked empty entry.

   *

   * When requesting an entry with size DAX_PMD, grab_mapping_entry() will

   * either return that locked entry or will return VM_FAULT_FALLBACK.
   * This will happen if there are any PTE entries within the PMD range
   * that we are requesting.

   *

   * We always favor PTE entries over PMD entries. There isn't a flow where we
   * evict PTE entries in order to 'upgrade' them to a PMD entry.  A PMD
   * insertion will fail if it finds any PTE entries already in the tree, and a
   * PTE insertion will cause an existing PMD entry to be unmapped and
   * downgraded to PTE entries.  This happens for both PMD zero pages as
   * well as PMD empty entries.

   *

   * The exception to this downgrade path is for PMD entries that have
   * real storage backing them.  We will leave these real PMD entries in
   * the tree, and PTE writes will simply dirty the entire PMD 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.

   *
   * On error, this function does not return an ERR_PTR.  Instead it returns
   * a VM_FAULT code, encoded as an xarray internal entry.  The ERR_PTR values
   * overlap with xarray value entries.

   */

  static void *grab_mapping_entry(struct xa_state *xas,

  		struct address_space *mapping, unsigned int order)

  {

  	unsigned long index = xas->xa_index;
  	bool pmd_downgrade = false; /* splitting PMD entry into PTE entries? */
  	void *entry;

  retry:
  	xas_lock_irq(xas);

  	entry = get_unlocked_entry(xas, order);

  	if (entry) {

  		if (dax_is_conflict(entry))
  			goto fallback;

  		if (!xa_is_value(entry)) {

  			xas_set_err(xas, -EIO);

  			goto out_unlock;
  		}

  		if (order == 0) {

  			if (dax_is_pmd_entry(entry) &&

  			    (dax_is_zero_entry(entry) ||
  			     dax_is_empty_entry(entry))) {
  				pmd_downgrade = true;
  			}
  		}
  	}

  	if (pmd_downgrade) {
  		/*
  		 * Make sure 'entry' remains valid while we drop
  		 * the i_pages lock.
  		 */
  		dax_lock_entry(xas, entry);

  		/*
  		 * Besides huge zero pages the only other thing that gets
  		 * downgraded are empty entries which don't need to be
  		 * unmapped.
  		 */

  		if (dax_is_zero_entry(entry)) {
  			xas_unlock_irq(xas);
  			unmap_mapping_pages(mapping,
  					xas->xa_index & ~PG_PMD_COLOUR,
  					PG_PMD_NR, false);
  			xas_reset(xas);
  			xas_lock_irq(xas);

  		}

  		dax_disassociate_entry(entry, mapping, false);
  		xas_store(xas, NULL);	/* undo the PMD join */
  		dax_wake_entry(xas, entry, true);
  		mapping->nrexceptional--;
  		entry = NULL;
  		xas_set(xas, index);
  	}

  	if (entry) {
  		dax_lock_entry(xas, entry);
  	} else {

  		unsigned long flags = DAX_EMPTY;
  
  		if (order > 0)
  			flags |= DAX_PMD;
  		entry = dax_make_entry(pfn_to_pfn_t(0), flags);

  		dax_lock_entry(xas, entry);
  		if (xas_error(xas))
  			goto out_unlock;

  		mapping->nrexceptional++;

  	}

  
  out_unlock:
  	xas_unlock_irq(xas);
  	if (xas_nomem(xas, mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM))
  		goto retry;
  	if (xas->xa_node == XA_ERROR(-ENOMEM))
  		return xa_mk_internal(VM_FAULT_OOM);
  	if (xas_error(xas))
  		return xa_mk_internal(VM_FAULT_SIGBUS);

  	return entry;

  fallback:
  	xas_unlock_irq(xas);
  	return xa_mk_internal(VM_FAULT_FALLBACK);

  }

  /**

   * dax_layout_busy_page_range - find first pinned page in @mapping

   * @mapping: address space to scan for a page with ref count > 1

   * @start: Starting offset. Page containing 'start' is included.
   * @end: End offset. Page containing 'end' is included. If 'end' is LLONG_MAX,
   *       pages from 'start' till the end of file are included.

   *
   * 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_range(struct address_space *mapping,
  					loff_t start, loff_t end)

  {

  	void *entry;
  	unsigned int scanned = 0;

  	struct page *page = NULL;

  	pgoff_t start_idx = start >> PAGE_SHIFT;
  	pgoff_t end_idx;
  	XA_STATE(xas, &mapping->i_pages, start_idx);

  
  	/*
  	 * 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;

  	/* If end == LLONG_MAX, all pages from start to till end of file */
  	if (end == LLONG_MAX)
  		end_idx = ULONG_MAX;
  	else
  		end_idx = end >> PAGE_SHIFT;

  	/*
  	 * If we race get_user_pages_fast() here either we'll see the

  	 * elevated page count in the iteration 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_pages() 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_pages(mapping, start_idx, end_idx - start_idx + 1, 0);

  	xas_lock_irq(&xas);

  	xas_for_each(&xas, entry, end_idx) {

  		if (WARN_ON_ONCE(!xa_is_value(entry)))
  			continue;
  		if (unlikely(dax_is_locked(entry)))

  			entry = get_unlocked_entry(&xas, 0);

  		if (entry)
  			page = dax_busy_page(entry);
  		put_unlocked_entry(&xas, entry);

  		if (page)
  			break;

  		if (++scanned % XA_CHECK_SCHED)
  			continue;
  
  		xas_pause(&xas);
  		xas_unlock_irq(&xas);
  		cond_resched();
  		xas_lock_irq(&xas);

  	}

  	xas_unlock_irq(&xas);

  	return page;
  }

  EXPORT_SYMBOL_GPL(dax_layout_busy_page_range);
  
  struct page *dax_layout_busy_page(struct address_space *mapping)
  {
  	return dax_layout_busy_page_range(mapping, 0, LLONG_MAX);
  }

  EXPORT_SYMBOL_GPL(dax_layout_busy_page);

  static int __dax_invalidate_entry(struct address_space *mapping,

  					  pgoff_t index, bool trunc)
  {

  	XA_STATE(xas, &mapping->i_pages, index);

  	int ret = 0;
  	void *entry;

  	xas_lock_irq(&xas);

  	entry = get_unlocked_entry(&xas, 0);

  	if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))

  		goto out;
  	if (!trunc &&

  	    (xas_get_mark(&xas, PAGECACHE_TAG_DIRTY) ||
  	     xas_get_mark(&xas, PAGECACHE_TAG_TOWRITE)))

  		goto out;

  	dax_disassociate_entry(entry, mapping, trunc);

  	xas_store(&xas, NULL);

  	mapping->nrexceptional--;
  	ret = 1;
  out:

  	put_unlocked_entry(&xas, entry);
  	xas_unlock_irq(&xas);

  	return ret;
  }

  /*

   * Delete DAX entry at @index from @mapping.  Wait for it
   * to be unlocked before deleting it.

   */
  int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
  {

  	int ret = __dax_invalidate_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

  	 * page cache (usually fs-private i_mmap_sem for writing). Since the

  	 * caller has seen a DAX entry for this index, we better find it

  	 * at that index as well...
  	 */

  	WARN_ON_ONCE(!ret);
  	return ret;
  }
  
  /*

   * Invalidate DAX entry if it is clean.

   */
  int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
  				      pgoff_t index)
  {

  	return __dax_invalidate_entry(mapping, index, false);

  }

  static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_dev,
  			     sector_t sector, struct page *to, unsigned long vaddr)

  {

  	void *vto, *kaddr;
  	pgoff_t pgoff;

  	long rc;
  	int id;

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

  	if (rc)
  		return rc;
  
  	id = dax_read_lock();

  	rc = dax_direct_access(dax_dev, pgoff, PHYS_PFN(PAGE_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_entry(struct xa_state *xas,
  		struct address_space *mapping, struct vm_fault *vmf,
  		void *entry, pfn_t pfn, unsigned long flags, bool dirty)

  {

  	void *new_entry = dax_make_entry(pfn, flags);

  	if (dirty)

  		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);

  	if (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE)) {

  		unsigned long index = xas->xa_index;

  		/* 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, index, 1, false);

  	}

  	xas_reset(xas);
  	xas_lock_irq(xas);

  	if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
  		void *old;

  		dax_disassociate_entry(entry, mapping, false);

  		dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address);

  		/*

  		 * Only swap our new entry into the page cache if the current

  		 * entry is a zero page or an empty entry.  If a normal PTE or

  		 * PMD entry is already in the cache, 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.
  		 */

  		old = dax_lock_entry(xas, new_entry);

  		WARN_ON_ONCE(old != xa_mk_value(xa_to_value(entry) |
  					DAX_LOCKED));

  		entry = new_entry;

  	} else {
  		xas_load(xas);	/* Walk the xa_state */

  	}

  	if (dirty)

  		xas_set_mark(xas, PAGECACHE_TAG_DIRTY);

  	xas_unlock_irq(xas);

  	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_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) {

  		struct mmu_notifier_range range;
  		unsigned long address;

  
  		cond_resched();
  
  		if (!(vma->vm_flags & VM_SHARED))
  			continue;
  
  		address = pgoff_address(index, vma);

  
  		/*

  		 * Note because we provide range 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, &range,
  				   &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_page(vma, address, pfn);

  			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(&range);

  	}
  	i_mmap_unlock_read(mapping);
  }

  static int dax_writeback_one(struct xa_state *xas, struct dax_device *dax_dev,
  		struct address_space *mapping, void *entry)

  {

  	unsigned long pfn, index, count;

  	long ret = 0;

  	/*

  	 * A page got tagged dirty in DAX mapping? Something is seriously
  	 * wrong.

  	 */

  	if (WARN_ON(!xa_is_value(entry)))

  		return -EIO;

  	if (unlikely(dax_is_locked(entry))) {
  		void *old_entry = entry;

  		entry = get_unlocked_entry(xas, 0);

  
  		/* Entry got punched out / reallocated? */
  		if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
  			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_to_pfn(old_entry) != dax_to_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 done this entry */
  		if (!xas_get_mark(xas, PAGECACHE_TAG_TOWRITE))
  			goto put_unlocked;

  	}

  	/* Lock the entry to serialize with page faults */

  	dax_lock_entry(xas, entry);

  	/*
  	 * 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.

  	 */

  	xas_clear_mark(xas, PAGECACHE_TAG_TOWRITE);
  	xas_unlock_irq(xas);

  	/*

  	 * If dax_writeback_mapping_range() was given a wbc->range_start
  	 * in the middle of a PMD, the 'index' we use needs to be
  	 * aligned to the start of the PMD.

  	 * This allows us to flush for PMD_SIZE and not have to worry about
  	 * partial PMD writebacks.

  	 */

  	pfn = dax_to_pfn(entry);

  	count = 1UL << dax_entry_order(entry);
  	index = xas->xa_index & ~(count - 1);

  	dax_entry_mkclean(mapping, index, pfn);
  	dax_flush(dax_dev, page_address(pfn_to_page(pfn)), count * PAGE_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.
  	 */

  	xas_reset(xas);
  	xas_lock_irq(xas);
  	xas_store(xas, entry);
  	xas_clear_mark(xas, PAGECACHE_TAG_DIRTY);
  	dax_wake_entry(xas, entry, false);

  	trace_dax_writeback_one(mapping->host, index, count);

  	return ret;

   put_unlocked:

  	put_unlocked_entry(xas, entry);

  	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 dax_device *dax_dev, struct writeback_control *wbc)

  {

  	XA_STATE(xas, &mapping->i_pages, wbc->range_start >> PAGE_SHIFT);

  	struct inode *inode = mapping->host;

  	pgoff_t end_index = wbc->range_end >> PAGE_SHIFT;

  	void *entry;
  	int ret = 0;
  	unsigned int scanned = 0;

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

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

  	trace_dax_writeback_range(inode, xas.xa_index, end_index);

  	tag_pages_for_writeback(mapping, xas.xa_index, end_index);

  	xas_lock_irq(&xas);
  	xas_for_each_marked(&xas, entry, end_index, PAGECACHE_TAG_TOWRITE) {
  		ret = dax_writeback_one(&xas, dax_dev, mapping, entry);
  		if (ret < 0) {
  			mapping_set_error(mapping, ret);

  			break;

  		}

  		if (++scanned % XA_CHECK_SCHED)
  			continue;
  
  		xas_pause(&xas);
  		xas_unlock_irq(&xas);
  		cond_resched();
  		xas_lock_irq(&xas);

  	}

  	xas_unlock_irq(&xas);

  	trace_dax_writeback_range_done(inode, xas.xa_index, end_index);
  	return ret;

  }
  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 xa_state *xas,
  		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;

  	*entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,

  			DAX_ZERO_PAGE, false);

  	ret = vmf_insert_mixed(vmf->vma, vaddr, pfn);

  	trace_dax_load_hole(inode, vmf, ret);
  	return ret;
  }

  s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)

  {

  	sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);

  	pgoff_t pgoff;
  	long rc, id;
  	void *kaddr;
  	bool page_aligned = false;

  	unsigned offset = offset_in_page(pos);
  	unsigned size = min_t(u64, PAGE_SIZE - offset, length);

  	if (IS_ALIGNED(sector << SECTOR_SHIFT, PAGE_SIZE) &&

  	    (size == PAGE_SIZE))

  		page_aligned = true;

  	rc = bdev_dax_pgoff(iomap->bdev, sector, PAGE_SIZE, &pgoff);

  	if (rc)
  		return rc;
  
  	id = dax_read_lock();
  
  	if (page_aligned)

  		rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);

  	else

  		rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);

  	if (rc < 0) {
  		dax_read_unlock(id);
  		return rc;
  	}
  
  	if (!page_aligned) {

  		memset(kaddr + offset, 0, size);

  		dax_flush(iomap->dax_dev, kaddr + offset, size);

  	}

  	dax_read_unlock(id);

  	return size;

  }

  static loff_t

  dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,

  		struct iomap *iomap, struct iomap *srcmap)

  {

  	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_write(&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;

  	return vmf_error(error);

  }

  /*
   * 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;

  	XA_STATE(xas, &mapping->i_pages, vmf->pgoff);

  	struct inode *inode = mapping->host;

  	unsigned long vaddr = vmf->address;

  	loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;

  	struct iomap iomap = { .type = IOMAP_HOLE };
  	struct iomap srcmap = { .type = IOMAP_HOLE };

  	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(&xas, mapping, 0);
  	if (xa_is_internal(entry)) {
  		ret = xa_to_internal(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, &srcmap);

  	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_cow_page_dax(iomap.bdev, iomap.dax_dev,
  						  sector, 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_entry(&xas, 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(&xas, mapping, &entry, vmf);

  			goto finish_iomap;

  		}

  		fallthrough;

  	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:

  	dax_unlock_entry(&xas, entry);

   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 xa_state *xas, 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 vm_area_struct *vma = vmf->vma;

  	struct inode *inode = mapping->host;

  	pgtable_t pgtable = NULL;

  	struct page *zero_page;
  	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);

  	*entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,

  			DAX_PMD | DAX_ZERO_PAGE, false);

  	if (arch_needs_pgtable_deposit()) {
  		pgtable = pte_alloc_one(vma->vm_mm);
  		if (!pgtable)
  			return VM_FAULT_OOM;
  	}

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

  		spin_unlock(ptl);

  		goto fallback;

  	}

  	if (pgtable) {
  		pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
  		mm_inc_nr_ptes(vma->vm_mm);
  	}

  	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, *entry);

  	return VM_FAULT_NOPAGE;

  
  fallback:

  	if (pgtable)
  		pte_free(vma->vm_mm, pgtable);

  	trace_dax_pmd_load_hole_fallback(inode, vmf, zero_page, *entry);

  	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;

  	XA_STATE_ORDER(xas, &mapping->i_pages, vmf->pgoff, PMD_ORDER);

  	unsigned long pmd_addr = vmf->address & PMD_MASK;
  	bool write = vmf->flags & FAULT_FLAG_WRITE;

  	bool sync;