/*
   * 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, 1);
  
  	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_page(vma, address, pfn);
  			pmd = pmdp_huge_clear_flush(vma, address, pmdp);
  			pmd = pmd_wrprotect(pmd);
  			pmd = pmd_mkclean(pmd);
  			set_pmd_at(vma->vm_mm, address, pmdp, pmd);

  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);
  	}

  	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(vma, vmf->address, vmf->pmd, 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);