[sfrench/cifs-2.6.git] / fs / dax.c

/*
 * 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;
}

/*
 * 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, bool (*wait_fn)(void))
{
        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 (;;) {
                bool revalidate;

                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);
                revalidate = wait_fn();
                finish_wait(wq, &ewait.wait);
                xa_lock_irq(&mapping->i_pages);
                if (revalidate)
                        return ERR_PTR(-EAGAIN);
        }
}

static bool entry_wait(void)
{
        schedule();
        /*
         * Never return an ERR_PTR() from
         * __get_unlocked_mapping_entry(), just keep looping.
         */
        return false;
}

static void *get_unlocked_mapping_entry(struct address_space *mapping,
                pgoff_t index, void ***slotp)
{
        return __get_unlocked_mapping_entry(mapping, index, slotp, entry_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;
}

static bool entry_wait_revalidate(void)
{
        rcu_read_unlock();
        schedule();
        rcu_read_lock();

        /*
         * Tell __get_unlocked_mapping_entry() to take a break, we need
         * to revalidate page->mapping after dropping locks
         */
        return true;
}

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 (!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 = __get_unlocked_mapping_entry(mapping, index, &slot,
                                entry_wait_revalidate);
                if (!entry) {
                        xa_unlock_irq(&mapping->i_pages);
                        break;
                } else if (IS_ERR(entry)) {
                        xa_unlock_irq(&mapping->i_pages);
                        WARN_ON_ONCE(PTR_ERR(entry) != -EAGAIN);
                        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)) {
                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);
                        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++;

                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);
                count_vm_event(THP_FAULT_FALLBACK);
        }
out:
        trace_dax_pmd_fault_done(inode, vmf, max_pgoff, result);
        return result;
}
#else
static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
                               const struct iomap_ops *ops)
{
        return VM_FAULT_FALLBACK;
}
#endif /* CONFIG_FS_DAX_PMD */

/**
 * dax_iomap_fault - handle a page fault on a DAX file
 * @vmf: The description of the fault
 * @pe_size: Size of the page to fault in
 * @pfnp: PFN to insert for synchronous faults if fsync is required
 * @iomap_errp: Storage for detailed error code in case of error
 * @ops: Iomap ops passed from the file system
 *
 * When a page fault occurs, filesystems may call this helper in
 * their fault handler for DAX files. dax_iomap_fault() assumes the caller
 * has done all the necessary locking for page fault to proceed
 * successfully.
 */
vm_fault_t dax_iomap_fault(struct vm_fault *vmf, enum page_entry_size pe_size,
                    pfn_t *pfnp, int *iomap_errp, const struct iomap_ops *ops)
{
        switch (pe_size) {
        case PE_SIZE_PTE:
                return dax_iomap_pte_fault(vmf, pfnp, iomap_errp, ops);
        case PE_SIZE_PMD:
                return dax_iomap_pmd_fault(vmf, pfnp, ops);
        default:
                return VM_FAULT_FALLBACK;
        }
}
EXPORT_SYMBOL_GPL(dax_iomap_fault);

/**
 * dax_insert_pfn_mkwrite - insert PTE or PMD entry into page tables
 * @vmf: The description of the fault
 * @pe_size: Size of entry to be inserted
 * @pfn: PFN to insert
 *
 * This function inserts writeable PTE or PMD entry into page tables for mmaped
 * DAX file.  It takes care of marking corresponding radix tree entry as dirty
 * as well.
 */
static vm_fault_t dax_insert_pfn_mkwrite(struct vm_fault *vmf,
                                  enum page_entry_size pe_size,
                                  pfn_t pfn)
{
        struct address_space *mapping = vmf->vma->vm_file->f_mapping;
        void *entry, **slot;
        pgoff_t index = vmf->pgoff;
        vm_fault_t ret;

        xa_lock_irq(&mapping->i_pages);
        entry = get_unlocked_mapping_entry(mapping, index, &slot);
        /* Did we race with someone splitting entry or so? */
        if (!entry ||
            (pe_size == PE_SIZE_PTE && !dax_is_pte_entry(entry)) ||
            (pe_size == PE_SIZE_PMD && !dax_is_pmd_entry(entry))) {
                put_unlocked_mapping_entry(mapping, index, entry);
                xa_unlock_irq(&mapping->i_pages);
                trace_dax_insert_pfn_mkwrite_no_entry(mapping->host, vmf,
                                                      VM_FAULT_NOPAGE);
                return VM_FAULT_NOPAGE;
        }
        radix_tree_tag_set(&mapping->i_pages, index, PAGECACHE_TAG_DIRTY);
        entry = lock_slot(mapping, slot);
        xa_unlock_irq(&mapping->i_pages);
        switch (pe_size) {
        case PE_SIZE_PTE:
                ret = vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
                break;
#ifdef CONFIG_FS_DAX_PMD
        case PE_SIZE_PMD:
                ret = vmf_insert_pfn_pmd(vmf->vma, vmf->address, vmf->pmd,
                        pfn, true);
                break;
#endif
        default:
                ret = VM_FAULT_FALLBACK;
        }
        put_locked_mapping_entry(mapping, index);
        trace_dax_insert_pfn_mkwrite(mapping->host, vmf, ret);
        return ret;
}

/**
 * dax_finish_sync_fault - finish synchronous page fault
 * @vmf: The description of the fault
 * @pe_size: Size of entry to be inserted
 * @pfn: PFN to insert
 *
 * This function ensures that the file range touched by the page fault is
 * stored persistently on the media and handles inserting of appropriate page
 * table entry.
 */
vm_fault_t dax_finish_sync_fault(struct vm_fault *vmf,
                enum page_entry_size pe_size, pfn_t pfn)
{
        int err;
        loff_t start = ((loff_t)vmf->pgoff) << PAGE_SHIFT;
        size_t len = 0;

        if (pe_size == PE_SIZE_PTE)
                len = PAGE_SIZE;
        else if (pe_size == PE_SIZE_PMD)
                len = PMD_SIZE;
        else
                WARN_ON_ONCE(1);
        err = vfs_fsync_range(vmf->vma->vm_file, start, start + len - 1, 1);
        if (err)
                return VM_FAULT_SIGBUS;
        return dax_insert_pfn_mkwrite(vmf, pe_size, pfn);
}
EXPORT_SYMBOL_GPL(dax_finish_sync_fault);