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 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * fs/dax.c - Direct Access filesystem code
  * Copyright (c) 2013-2014 Intel Corporation
  * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
  * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
  */
 
 #include <linux/atomic.h>
 #include <linux/blkdev.h>
 #include <linux/buffer_head.h>
 #include <linux/dax.h>
 #include <linux/fs.h>
 #include <linux/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 <linux/rmap.h>
 #include <asm/pgalloc.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/fs_dax.h>
 
 static inline unsigned int pe_order(enum page_entry_size pe_size)
 {
     if (pe_size == PE_SIZE_PTE)
         return PAGE_SHIFT - PAGE_SHIFT;
     if (pe_size == PE_SIZE_PMD)
         return PMD_SHIFT - PAGE_SHIFT;
     if (pe_size == PE_SIZE_PUD)
         return PUD_SHIFT - PAGE_SHIFT;
     return ~0;
 }
 
 /* We choose 4096 entries - same as per-zone page wait tables */
 #define DAX_WAIT_TABLE_BITS 12
 #define DAX_WAIT_TABLE_ENTRIES (1 << DAX_WAIT_TABLE_BITS)
 
 /* The 'colour' (ie low bits) within a PMD of a page offset.  */
 #define PG_PMD_COLOUR   ((PMD_SIZE >> PAGE_SHIFT) - 1)
 #define PG_PMD_NR   (PMD_SIZE >> PAGE_SHIFT)
 
 /* The order of a PMD entry */
 #define PMD_ORDER   (PMD_SHIFT - PAGE_SHIFT)
 
 static wait_queue_head_t wait_table[DAX_WAIT_TABLE_ENTRIES];
 
 static int __init init_dax_wait_table(void)
 {
     int i;
 
     for (i = 0; i < DAX_WAIT_TABLE_ENTRIES; i++)
         init_waitqueue_head(wait_table + i);
     return 0;
 }
 fs_initcall(init_dax_wait_table);
 
 /*
  * DAX pagecache entries use XArray value entries so they can't be mistaken
  * for pages.  We use one bit for locking, one bit for the entry size (PMD)
  * and two more to tell us if the entry is a zero page or an empty entry that
  * is just used for locking.  In total four special bits.
  *
  * If the PMD bit isn't set the entry has size PAGE_SIZE, and if the ZERO_PAGE
  * and EMPTY bits aren't set the entry is a normal DAX entry with a filesystem
  * block allocation.
  */
 #define DAX_SHIFT   (4)
 #define DAX_LOCKED  (1UL << 0)
 #define DAX_PMD     (1UL << 1)
 #define DAX_ZERO_PAGE   (1UL << 2)
 #define DAX_EMPTY   (1UL << 3)
 
 static unsigned long dax_to_pfn(void *entry)
 {
     return xa_to_value(entry) >> DAX_SHIFT;
 }
 
 static void *dax_make_entry(pfn_t pfn, unsigned long flags)
 {
     return xa_mk_value(flags | (pfn_t_to_pfn(pfn) << DAX_SHIFT));
 }
 
 static bool dax_is_locked(void *entry)
 {
     return xa_to_value(entry) & DAX_LOCKED;
 }
 
 static unsigned int dax_entry_order(void *entry)
 {
     if (xa_to_value(entry) & DAX_PMD)
         return PMD_ORDER;
     return 0;
 }
 
 static unsigned long dax_is_pmd_entry(void *entry)
 {
     return xa_to_value(entry) & DAX_PMD;
 }
 
 static bool dax_is_pte_entry(void *entry)
 {
     return !(xa_to_value(entry) & DAX_PMD);
 }
 
 static int dax_is_zero_entry(void *entry)
 {
     return xa_to_value(entry) & DAX_ZERO_PAGE;
 }
 
 static int dax_is_empty_entry(void *entry)
 {
     return xa_to_value(entry) & DAX_EMPTY;
 }
 
 /*
  * true if the entry that was found is of a smaller order than the entry
  * we were looking for
  */
 static bool dax_is_conflict(void *entry)
 {
     return entry == XA_RETRY_ENTRY;
 }
 
 /*
  * DAX page cache entry locking
  */
 struct exceptional_entry_key {
     struct xarray *xa;
     pgoff_t entry_start;
 };
 
 struct wait_exceptional_entry_queue {
     wait_queue_entry_t wait;
     struct exceptional_entry_key key;
 };
 
 /**
  * enum dax_wake_mode: waitqueue wakeup behaviour
  * @WAKE_ALL: wake all waiters in the waitqueue
  * @WAKE_NEXT: wake only the first waiter in the waitqueue
  */
 enum dax_wake_mode {
     WAKE_ALL,
     WAKE_NEXT,
 };
 
 static wait_queue_head_t *dax_entry_waitqueue(struct xa_state *xas,
         void *entry, struct exceptional_entry_key *key)
 {
     unsigned long hash;
     unsigned long index = xas->xa_index;
 
     /*
      * If 'entry' is a PMD, align the 'index' that we use for the wait
      * queue to the start of that PMD.  This ensures that all offsets in
      * the range covered by the PMD map to the same bit lock.
      */
     if (dax_is_pmd_entry(entry))
         index &= ~PG_PMD_COLOUR;
     key->xa = xas->xa;
     key->entry_start = index;
 
     hash = hash_long((unsigned long)xas->xa ^ index, DAX_WAIT_TABLE_BITS);
     return wait_table + hash;
 }
 
 static int wake_exceptional_entry_func(wait_queue_entry_t *wait,
         unsigned int mode, int sync, void *keyp)
 {
     struct exceptional_entry_key *key = keyp;
     struct wait_exceptional_entry_queue *ewait =
         container_of(wait, struct wait_exceptional_entry_queue, wait);
 
     if (key->xa != ewait->key.xa ||
         key->entry_start != ewait->key.entry_start)
         return 0;
     return autoremove_wake_function(wait, mode, sync, NULL);
 }
 
 /*
  * @entry may no longer be the entry at the index in the mapping.
  * The important information it's conveying is whether the entry at
  * this index used to be a PMD entry.
  */
 static void dax_wake_entry(struct xa_state *xas, void *entry,
                enum dax_wake_mode mode)
 {
     struct exceptional_entry_key key;
     wait_queue_head_t *wq;
 
     wq = dax_entry_waitqueue(xas, entry, &key);
 
     /*
      * Checking for locked entry and prepare_to_wait_exclusive() happens
      * under the i_pages lock, ditto for entry handling in our callers.
      * So at this point all tasks that could have seen our entry locked
      * must be in the waitqueue and the following check will see them.
      */
     if (waitqueue_active(wq))
         __wake_up(wq, TASK_NORMAL, mode == WAKE_ALL ? 0 : 1, &key);
 }
 
 /*
  * Look up entry in page cache, wait for it to become unlocked if it
  * is a DAX entry and return it.  The caller must subsequently call
  * put_unlocked_entry() if it did not lock the entry or dax_unlock_entry()
  * if it did.  The entry returned may have a larger order than @order.
  * If @order is larger than the order of the entry found in i_pages, this
  * function returns a dax_is_conflict entry.
  *
  * Must be called with the i_pages lock held.
  */
 static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)
 {
     void *entry;
     struct wait_exceptional_entry_queue ewait;
     wait_queue_head_t *wq;
 
     init_wait(&ewait.wait);
     ewait.wait.func = wake_exceptional_entry_func;
 
     for (;;) {
         entry = xas_find_conflict(xas);
         if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
             return entry;
         if (dax_entry_order(entry) < order)
             return XA_RETRY_ENTRY;
         if (!dax_is_locked(entry))
             return entry;
 
         wq = dax_entry_waitqueue(xas, entry, &ewait.key);
         prepare_to_wait_exclusive(wq, &ewait.wait,
                       TASK_UNINTERRUPTIBLE);
         xas_unlock_irq(xas);
         xas_reset(xas);
         schedule();
         finish_wait(wq, &ewait.wait);
         xas_lock_irq(xas);
     }
 }
 
 /*
  * The only thing keeping the address space around is the i_pages lock
  * (it's cycled in clear_inode() after removing the entries from i_pages)
  * After we call xas_unlock_irq(), we cannot touch xas->xa.
  */
 static void wait_entry_unlocked(struct xa_state *xas, void *entry)
 {
     struct wait_exceptional_entry_queue ewait;
     wait_queue_head_t *wq;
 
     init_wait(&ewait.wait);
     ewait.wait.func = wake_exceptional_entry_func;
 
     wq = dax_entry_waitqueue(xas, entry, &ewait.key);
     /*
      * Unlike get_unlocked_entry() there is no guarantee that this
      * path ever successfully retrieves an unlocked entry before an
      * inode dies. Perform a non-exclusive wait in case this path
      * never successfully performs its own wake up.
      */
     prepare_to_wait(wq, &ewait.wait, TASK_UNINTERRUPTIBLE);
     xas_unlock_irq(xas);
     schedule();
     finish_wait(wq, &ewait.wait);
 }
 
 static void put_unlocked_entry(struct xa_state *xas, void *entry,
                    enum dax_wake_mode mode)
 {
     if (entry && !dax_is_conflict(entry))
         dax_wake_entry(xas, entry, mode);
 }
 
 /*
  * We used the xa_state to get the entry, but then we locked the entry and
  * dropped the xa_lock, so we know the xa_state is stale and must be reset
  * before use.
  */
 static void dax_unlock_entry(struct xa_state *xas, void *entry)
 {
     void *old;
 
     BUG_ON(dax_is_locked(entry));
     xas_reset(xas);
     xas_lock_irq(xas);
     old = xas_store(xas, entry);
     xas_unlock_irq(xas);
     BUG_ON(!dax_is_locked(old));
     dax_wake_entry(xas, entry, WAKE_NEXT);
 }
 
 /*
  * Return: The entry stored at this location before it was locked.
  */
 static void *dax_lock_entry(struct xa_state *xas, void *entry)
 {
     unsigned long v = xa_to_value(entry);
     return xas_store(xas, xa_mk_value(v | DAX_LOCKED));
 }
 
 static unsigned long dax_entry_size(void *entry)
 {
     if (dax_is_zero_entry(entry))
         return 0;
     else if (dax_is_empty_entry(entry))
         return 0;
     else if (dax_is_pmd_entry(entry))
         return PMD_SIZE;
     else
         return PAGE_SIZE;
 }
 
 static unsigned long dax_end_pfn(void *entry)
 {
     return dax_to_pfn(entry) + dax_entry_size(entry) / PAGE_SIZE;
 }
 
 /*
  * Iterate through all mapped pfns represented by an entry, i.e. skip
  * 'empty' and 'zero' entries.
  */
 #define for_each_mapped_pfn(entry, pfn) \
     for (pfn = dax_to_pfn(entry); \
             pfn < dax_end_pfn(entry); pfn++)
 
 static inline bool dax_mapping_is_cow(struct address_space *mapping)
 {
     return (unsigned long)mapping == PAGE_MAPPING_DAX_COW;
 }
 
 /*
  * Set the page->mapping with FS_DAX_MAPPING_COW flag, increase the refcount.
  */
 static inline void dax_mapping_set_cow(struct page *page)
 {
     if ((uintptr_t)page->mapping != PAGE_MAPPING_DAX_COW) {
         /*
          * Reset the index if the page was already mapped
          * regularly before.
          */
         if (page->mapping)
             page->index = 1;
         page->mapping = (void *)PAGE_MAPPING_DAX_COW;
     }
     page->index++;
 }
 
 /*
  * When it is called in dax_insert_entry(), the cow flag will indicate that
  * whether this entry is shared by multiple files.  If so, set the page->mapping
  * FS_DAX_MAPPING_COW, and use page->index as refcount.
  */
 static void dax_associate_entry(void *entry, struct address_space *mapping,
         struct vm_area_struct *vma, unsigned long address, bool cow)
 {
     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);
 
         if (cow) {
             dax_mapping_set_cow(page);
         } else {
             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);
         if (dax_mapping_is_cow(page->mapping)) {
             /* keep the CoW flag if this page is still shared */
             if (page->index-- > 0)
                 continue;
         } else
             WARN_ON_ONCE(page->mapping && page->mapping != mapping);
         page->mapping = NULL;
         page->index = 0;
     }
 }
 
 static struct page *dax_busy_page(void *entry)
 {
     unsigned long pfn;
 
     for_each_mapped_pfn(entry, pfn) {
         struct page *page = pfn_to_page(pfn);
 
         if (page_ref_count(page) > 1)
             return page;
     }
     return NULL;
 }
 
 /*
  * dax_lock_page - Lock the DAX entry corresponding to a page
  * @page: The page whose entry we want to lock
  *
  * Context: Process context.
  * Return: A cookie to pass to dax_unlock_page() or 0 if the entry could
  * not be locked.
  */
 dax_entry_t dax_lock_page(struct page *page)
 {
     XA_STATE(xas, NULL, 0);
     void *entry;
 
     /* Ensure page->mapping isn't freed while we look at it */
     rcu_read_lock();
     for (;;) {
         struct address_space *mapping = READ_ONCE(page->mapping);
 
         entry = NULL;
         if (!mapping || !dax_mapping(mapping))
             break;
 
         /*
          * In the device-dax case there's no need to lock, a
          * struct dev_pagemap pin is sufficient to keep the
          * inode alive, and we assume we have dev_pagemap pin
          * otherwise we would not have a valid pfn_to_page()
          * translation.
          */
         entry = (void *)~0UL;
         if (S_ISCHR(mapping->host->i_mode))
             break;
 
         xas.xa = &mapping->i_pages;
         xas_lock_irq(&xas);
         if (mapping != page->mapping) {
             xas_unlock_irq(&xas);
             continue;
         }
         xas_set(&xas, page->index);
         entry = xas_load(&xas);
         if (dax_is_locked(entry)) {
             rcu_read_unlock();
             wait_entry_unlocked(&xas, entry);
             rcu_read_lock();
             continue;
         }
         dax_lock_entry(&xas, entry);
         xas_unlock_irq(&xas);
         break;
     }
     rcu_read_unlock();
     return (dax_entry_t)entry;
 }
 
 void dax_unlock_page(struct page *page, dax_entry_t cookie)
 {
     struct address_space *mapping = page->mapping;
     XA_STATE(xas, &mapping->i_pages, page->index);
 
     if (S_ISCHR(mapping->host->i_mode))
         return;
 
     dax_unlock_entry(&xas, (void *)cookie);
 }
 
 /*
  * dax_lock_mapping_entry - Lock the DAX entry corresponding to a mapping
  * @mapping: the file's mapping whose entry we want to lock
  * @index: the offset within this file
  * @page: output the dax page corresponding to this dax entry
  *
  * Return: A cookie to pass to dax_unlock_mapping_entry() or 0 if the entry
  * could not be locked.
  */
 dax_entry_t dax_lock_mapping_entry(struct address_space *mapping, pgoff_t index,
         struct page **page)
 {
     XA_STATE(xas, NULL, 0);
     void *entry;
 
     rcu_read_lock();
     for (;;) {
         entry = NULL;
         if (!dax_mapping(mapping))
             break;
 
         xas.xa = &mapping->i_pages;
         xas_lock_irq(&xas);
         xas_set(&xas, index);
         entry = xas_load(&xas);
         if (dax_is_locked(entry)) {
             rcu_read_unlock();
             wait_entry_unlocked(&xas, entry);
             rcu_read_lock();
             continue;
         }
         if (!entry ||
             dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
             /*
              * Because we are looking for entry from file's mapping
              * and index, so the entry may not be inserted for now,
              * or even a zero/empty entry.  We don't think this is
              * an error case.  So, return a special value and do
              * not output @page.
              */
             entry = (void *)~0UL;
         } else {
             *page = pfn_to_page(dax_to_pfn(entry));
             dax_lock_entry(&xas, entry);
         }
         xas_unlock_irq(&xas);
         break;
     }
     rcu_read_unlock();
     return (dax_entry_t)entry;
 }
 
 void dax_unlock_mapping_entry(struct address_space *mapping, pgoff_t index,
         dax_entry_t cookie)
 {
     XA_STATE(xas, &mapping->i_pages, index);
 
     if (cookie == ~0UL)
         return;
 
     dax_unlock_entry(&xas, (void *)cookie);
 }
 
 /*
  * Find page cache entry at given index. If it is a DAX entry, return it
  * with the entry locked. If the page cache doesn't contain an entry at
  * that index, add a locked empty entry.
  *
  * When requesting an entry with size DAX_PMD, grab_mapping_entry() will
  * either return that locked entry or will return VM_FAULT_FALLBACK.
  * This will happen if there are any PTE entries within the PMD range
  * that we are requesting.
  *
  * We always favor PTE entries over PMD entries. There isn't a flow where we
  * evict PTE entries in order to 'upgrade' them to a PMD entry.  A PMD
  * insertion will fail if it finds any PTE entries already in the tree, and a
  * PTE insertion will cause an existing PMD entry to be unmapped and
  * downgraded to PTE entries.  This happens for both PMD zero pages as
  * well as PMD empty entries.
  *
  * The exception to this downgrade path is for PMD entries that have
  * real storage backing them.  We will leave these real PMD entries in
  * the tree, and PTE writes will simply dirty the entire PMD entry.
  *
  * Note: Unlike filemap_fault() we don't honor FAULT_FLAG_RETRY flags. For
  * persistent memory the benefit is doubtful. We can add that later if we can
  * show it helps.
  *
  * On error, this function does not return an ERR_PTR.  Instead it returns
  * a VM_FAULT code, encoded as an xarray internal entry.  The ERR_PTR values
  * overlap with xarray value entries.
  */
 static void *grab_mapping_entry(struct xa_state *xas,
         struct address_space *mapping, unsigned int order)
 {
     unsigned long index = xas->xa_index;
     bool pmd_downgrade; /* splitting PMD entry into PTE entries? */
     void *entry;
 
 retry:
     pmd_downgrade = false;
     xas_lock_irq(xas);
     entry = get_unlocked_entry(xas, order);
 
     if (entry) {
         if (dax_is_conflict(entry))
             goto fallback;
         if (!xa_is_value(entry)) {
             xas_set_err(xas, -EIO);
             goto out_unlock;
         }
 
         if (order == 0) {
             if (dax_is_pmd_entry(entry) &&
                 (dax_is_zero_entry(entry) ||
                  dax_is_empty_entry(entry))) {
                 pmd_downgrade = true;
             }
         }
     }
 
     if (pmd_downgrade) {
         /*
          * Make sure 'entry' remains valid while we drop
          * the i_pages lock.
          */
         dax_lock_entry(xas, entry);
 
         /*
          * Besides huge zero pages the only other thing that gets
          * downgraded are empty entries which don't need to be
          * unmapped.
          */
         if (dax_is_zero_entry(entry)) {
             xas_unlock_irq(xas);
             unmap_mapping_pages(mapping,
                     xas->xa_index & ~PG_PMD_COLOUR,
                     PG_PMD_NR, false);
             xas_reset(xas);
             xas_lock_irq(xas);
         }
 
         dax_disassociate_entry(entry, mapping, false);
         xas_store(xas, NULL);   /* undo the PMD join */
         dax_wake_entry(xas, entry, WAKE_ALL);
         mapping->nrpages -= PG_PMD_NR;
         entry = NULL;
         xas_set(xas, index);
     }
 
     if (entry) {
         dax_lock_entry(xas, entry);
     } else {
         unsigned long flags = DAX_EMPTY;
 
         if (order > 0)
             flags |= DAX_PMD;
         entry = dax_make_entry(pfn_to_pfn_t(0), flags);
         dax_lock_entry(xas, entry);
         if (xas_error(xas))
             goto out_unlock;
         mapping->nrpages += 1UL << order;
     }
 
 out_unlock:
     xas_unlock_irq(xas);
     if (xas_nomem(xas, mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM))
         goto retry;
     if (xas->xa_node == XA_ERROR(-ENOMEM))
         return xa_mk_internal(VM_FAULT_OOM);
     if (xas_error(xas))
         return xa_mk_internal(VM_FAULT_SIGBUS);
     return entry;
 fallback:
     xas_unlock_irq(xas);
     return xa_mk_internal(VM_FAULT_FALLBACK);
 }
 
 /**
  * dax_layout_busy_page_range - find first pinned page in @mapping
  * @mapping: address space to scan for a page with ref count > 1
  * @start: Starting offset. Page containing 'start' is included.
  * @end: End offset. Page containing 'end' is included. If 'end' is LLONG_MAX,
  *       pages from 'start' till the end of file are included.
  *
  * DAX requires ZONE_DEVICE mapped pages. These pages are never
  * 'onlined' to the page allocator so they are considered idle when
  * page->count == 1. A filesystem uses this interface to determine if
  * any page in the mapping is busy, i.e. for DMA, or other
  * get_user_pages() usages.
  *
  * It is expected that the filesystem is holding locks to block the
  * establishment of new mappings in this address_space. I.e. it expects
  * to be able to run unmap_mapping_range() and subsequently not race
  * mapping_mapped() becoming true.
  */
 struct page *dax_layout_busy_page_range(struct address_space *mapping,
                     loff_t start, loff_t end)
 {
     void *entry;
     unsigned int scanned = 0;
     struct page *page = NULL;
     pgoff_t start_idx = start >> PAGE_SHIFT;
     pgoff_t end_idx;
     XA_STATE(xas, &mapping->i_pages, start_idx);
 
     /*
      * In the 'limited' case get_user_pages() for dax is disabled.
      */
     if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
         return NULL;
 
     if (!dax_mapping(mapping) || !mapping_mapped(mapping))
         return NULL;
 
     /* If end == LLONG_MAX, all pages from start to till end of file */
     if (end == LLONG_MAX)
         end_idx = ULONG_MAX;
     else
         end_idx = end >> PAGE_SHIFT;
     /*
      * If we race get_user_pages_fast() here either we'll see the
      * elevated page count in the iteration and wait, or
      * get_user_pages_fast() will see that the page it took a reference
      * against is no longer mapped in the page tables and bail to the
      * get_user_pages() slow path.  The slow path is protected by
      * pte_lock() and pmd_lock(). New references are not taken without
      * holding those locks, and unmap_mapping_pages() will not zero the
      * pte or pmd without holding the respective lock, so we are
      * guaranteed to either see new references or prevent new
      * references from being established.
      */
     unmap_mapping_pages(mapping, start_idx, end_idx - start_idx + 1, 0);
 
     xas_lock_irq(&xas);
     xas_for_each(&xas, entry, end_idx) {
         if (WARN_ON_ONCE(!xa_is_value(entry)))
             continue;
         if (unlikely(dax_is_locked(entry)))
             entry = get_unlocked_entry(&xas, 0);
         if (entry)
             page = dax_busy_page(entry);
         put_unlocked_entry(&xas, entry, WAKE_NEXT);
         if (page)
             break;
         if (++scanned % XA_CHECK_SCHED)
             continue;
 
         xas_pause(&xas);
         xas_unlock_irq(&xas);
         cond_resched();
         xas_lock_irq(&xas);
     }
     xas_unlock_irq(&xas);
     return page;
 }
 EXPORT_SYMBOL_GPL(dax_layout_busy_page_range);
 
 struct page *dax_layout_busy_page(struct address_space *mapping)
 {
     return dax_layout_busy_page_range(mapping, 0, LLONG_MAX);
 }
 EXPORT_SYMBOL_GPL(dax_layout_busy_page);
 
 static int __dax_invalidate_entry(struct address_space *mapping,
                       pgoff_t index, bool trunc)
 {
     XA_STATE(xas, &mapping->i_pages, index);
     int ret = 0;
     void *entry;
 
     xas_lock_irq(&xas);
     entry = get_unlocked_entry(&xas, 0);
     if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
         goto out;
     if (!trunc &&
         (xas_get_mark(&xas, PAGECACHE_TAG_DIRTY) ||
          xas_get_mark(&xas, PAGECACHE_TAG_TOWRITE)))
         goto out;
     dax_disassociate_entry(entry, mapping, trunc);
     xas_store(&xas, NULL);
     mapping->nrpages -= 1UL << dax_entry_order(entry);
     ret = 1;
 out:
     put_unlocked_entry(&xas, entry, WAKE_ALL);
     xas_unlock_irq(&xas);
     return ret;
 }
 
 /*
  * Delete DAX entry at @index from @mapping.  Wait for it
  * to be unlocked before deleting it.
  */
 int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
 {
     int ret = __dax_invalidate_entry(mapping, index, true);
 
     /*
      * This gets called from truncate / punch_hole path. As such, the caller
      * must hold locks protecting against concurrent modifications of the
      * page cache (usually fs-private i_mmap_sem for writing). Since the
      * caller has seen a DAX entry for this index, we better find it
      * at that index as well...
      */
     WARN_ON_ONCE(!ret);
     return ret;
 }
 
 /*
  * Invalidate DAX entry if it is clean.
  */
 int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
                       pgoff_t index)
 {
     return __dax_invalidate_entry(mapping, index, false);
 }
 
 static pgoff_t dax_iomap_pgoff(const struct iomap *iomap, loff_t pos)
 {
     return PHYS_PFN(iomap->addr + (pos & PAGE_MASK) - iomap->offset);
 }
 
 static int copy_cow_page_dax(struct vm_fault *vmf, const struct iomap_iter *iter)
 {
     pgoff_t pgoff = dax_iomap_pgoff(&iter->iomap, iter->pos);
     void *vto, *kaddr;
     long rc;
     int id;
 
     id = dax_read_lock();
     rc = dax_direct_access(iter->iomap.dax_dev, pgoff, 1, DAX_ACCESS,
                 &kaddr, NULL);
     if (rc < 0) {
         dax_read_unlock(id);
         return rc;
     }
     vto = kmap_atomic(vmf->cow_page);
     copy_user_page(vto, kaddr, vmf->address, vmf->cow_page);
     kunmap_atomic(vto);
     dax_read_unlock(id);
     return 0;
 }
 
 /*
  * 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(const struct iomap_iter *iter,
         struct vm_area_struct *vma)
 {
     return (iter->flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC) &&
         (iter->iomap.flags & IOMAP_F_DIRTY);
 }
 
 static bool dax_fault_is_cow(const struct iomap_iter *iter)
 {
     return (iter->flags & IOMAP_WRITE) &&
         (iter->iomap.flags & IOMAP_F_SHARED);
 }
 
 /*
  * By this point grab_mapping_entry() has ensured that we have a locked entry
  * of the appropriate size so we don't have to worry about downgrading PMDs to
  * PTEs.  If we happen to be trying to insert a PTE and there is a PMD
  * already in the tree, we will skip the insertion and just dirty the PMD as
  * appropriate.
  */
 static void *dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf,
         const struct iomap_iter *iter, void *entry, pfn_t pfn,
         unsigned long flags)
 {
     struct address_space *mapping = vmf->vma->vm_file->f_mapping;
     void *new_entry = dax_make_entry(pfn, flags);
     bool dirty = !dax_fault_is_synchronous(iter, vmf->vma);
     bool cow = dax_fault_is_cow(iter);
 
     if (dirty)
         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 
     if (cow || (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE))) {
         unsigned long index = xas->xa_index;
         /* we are replacing a zero page with block mapping */
         if (dax_is_pmd_entry(entry))
             unmap_mapping_pages(mapping, index & ~PG_PMD_COLOUR,
                     PG_PMD_NR, false);
         else /* pte entry */
             unmap_mapping_pages(mapping, index, 1, false);
     }
 
     xas_reset(xas);
     xas_lock_irq(xas);
     if (cow || dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
         void *old;
 
         dax_disassociate_entry(entry, mapping, false);
         dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address,
                 cow);
         /*
          * Only swap our new entry into the page cache if the current
          * entry is a zero page or an empty entry.  If a normal PTE or
          * PMD entry is already in the cache, we leave it alone.  This
          * means that if we are trying to insert a PTE and the
          * existing entry is a PMD, we will just leave the PMD in the
          * tree and dirty it if necessary.
          */
         old = dax_lock_entry(xas, new_entry);
         WARN_ON_ONCE(old != xa_mk_value(xa_to_value(entry) |
                     DAX_LOCKED));
         entry = new_entry;
     } else {
         xas_load(xas);  /* Walk the xa_state */
     }
 
     if (dirty)
         xas_set_mark(xas, PAGECACHE_TAG_DIRTY);
 
     if (cow)
         xas_set_mark(xas, PAGECACHE_TAG_TOWRITE);
 
     xas_unlock_irq(xas);
     return entry;
 }
 
 static int dax_writeback_one(struct xa_state *xas, struct dax_device *dax_dev,
         struct address_space *mapping, void *entry)
 {
     unsigned long pfn, index, count, end;
     long ret = 0;
     struct vm_area_struct *vma;
 
     /*
      * A page got tagged dirty in DAX mapping? Something is seriously
      * wrong.
      */
     if (WARN_ON(!xa_is_value(entry)))
         return -EIO;
 
     if (unlikely(dax_is_locked(entry))) {
         void *old_entry = entry;
 
         entry = get_unlocked_entry(xas, 0);
 
         /* Entry got punched out / reallocated? */
         if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
             goto put_unlocked;
         /*
          * Entry got reallocated elsewhere? No need to writeback.
          * We have to compare pfns as we must not bail out due to
          * difference in lockbit or entry type.
          */
         if (dax_to_pfn(old_entry) != dax_to_pfn(entry))
             goto put_unlocked;
         if (WARN_ON_ONCE(dax_is_empty_entry(entry) ||
                     dax_is_zero_entry(entry))) {
             ret = -EIO;
             goto put_unlocked;
         }
 
         /* Another fsync thread may have already done this entry */
         if (!xas_get_mark(xas, PAGECACHE_TAG_TOWRITE))
             goto put_unlocked;
     }
 
     /* Lock the entry to serialize with page faults */
     dax_lock_entry(xas, entry);
 
     /*
      * We can clear the tag now but we have to be careful so that concurrent
      * dax_writeback_one() calls for the same index cannot finish before we
      * actually flush the caches. This is achieved as the calls will look
      * at the entry only under the i_pages lock and once they do that
      * they will see the entry locked and wait for it to unlock.
      */
     xas_clear_mark(xas, PAGECACHE_TAG_TOWRITE);
     xas_unlock_irq(xas);
 
     /*
      * If dax_writeback_mapping_range() was given a wbc->range_start
      * in the middle of a PMD, the 'index' we use needs to be
      * aligned to the start of the PMD.
      * This allows us to flush for PMD_SIZE and not have to worry about
      * partial PMD writebacks.
      */
     pfn = dax_to_pfn(entry);
     count = 1UL << dax_entry_order(entry);
     index = xas->xa_index & ~(count - 1);
     end = index + count - 1;
 
     /* Walk all mappings of a given index of a file and writeprotect them */
     i_mmap_lock_read(mapping);
     vma_interval_tree_foreach(vma, &mapping->i_mmap, index, end) {
         pfn_mkclean_range(pfn, count, index, vma);
         cond_resched();
     }
     i_mmap_unlock_read(mapping);
 
     dax_flush(dax_dev, page_address(pfn_to_page(pfn)), count * PAGE_SIZE);
     /*
      * After we have flushed the cache, we can clear the dirty tag. There
      * cannot be new dirty data in the pfn after the flush has completed as
      * the pfn mappings are writeprotected and fault waits for mapping
      * entry lock.
      */
     xas_reset(xas);
     xas_lock_irq(xas);
     xas_store(xas, entry);
     xas_clear_mark(xas, PAGECACHE_TAG_DIRTY);
     dax_wake_entry(xas, entry, WAKE_NEXT);
 
     trace_dax_writeback_one(mapping->host, index, count);
     return ret;
 
  put_unlocked:
     put_unlocked_entry(xas, entry, WAKE_NEXT);
     return ret;
 }
 
 /*
  * Flush the mapping to the persistent domain within the byte range of [start,
  * end]. This is required by data integrity operations to ensure file data is
  * on persistent storage prior to completion of the operation.
  */
 int dax_writeback_mapping_range(struct address_space *mapping,
         struct dax_device *dax_dev, struct writeback_control *wbc)
 {
     XA_STATE(xas, &mapping->i_pages, wbc->range_start >> PAGE_SHIFT);
     struct inode *inode = mapping->host;
     pgoff_t end_index = wbc->range_end >> PAGE_SHIFT;
     void *entry;
     int ret = 0;
     unsigned int scanned = 0;
 
     if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))
         return -EIO;
 
     if (mapping_empty(mapping) || wbc->sync_mode != WB_SYNC_ALL)
         return 0;
 
     trace_dax_writeback_range(inode, xas.xa_index, end_index);
 
     tag_pages_for_writeback(mapping, xas.xa_index, end_index);
 
     xas_lock_irq(&xas);
     xas_for_each_marked(&xas, entry, end_index, PAGECACHE_TAG_TOWRITE) {
         ret = dax_writeback_one(&xas, dax_dev, mapping, entry);
         if (ret < 0) {
             mapping_set_error(mapping, ret);
             break;
         }
         if (++scanned % XA_CHECK_SCHED)
             continue;
 
         xas_pause(&xas);
         xas_unlock_irq(&xas);
         cond_resched();
         xas_lock_irq(&xas);
     }
     xas_unlock_irq(&xas);
     trace_dax_writeback_range_done(inode, xas.xa_index, end_index);
     return ret;
 }
 EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
 
 static int dax_iomap_direct_access(const struct iomap *iomap, loff_t pos,
         size_t size, void **kaddr, pfn_t *pfnp)
 {
     pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
     int id, rc = 0;
     long length;
 
     id = dax_read_lock();
     length = dax_direct_access(iomap->dax_dev, pgoff, PHYS_PFN(size),
                    DAX_ACCESS, kaddr, pfnp);
     if (length < 0) {
         rc = length;
         goto out;
     }
     if (!pfnp)
         goto out_check_addr;
     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_check_addr:
     if (!kaddr)
         goto out;
     if (!*kaddr)
         rc = -EFAULT;
 out:
     dax_read_unlock(id);
     return rc;
 }
 
 /**
  * dax_iomap_cow_copy - Copy the data from source to destination before write
  * @pos:    address to do copy from.
  * @length: size of copy operation.
  * @align_size: aligned w.r.t align_size (either PMD_SIZE or PAGE_SIZE)
  * @srcmap: iomap srcmap
  * @daddr:  destination address to copy to.
  *
  * This can be called from two places. Either during DAX write fault (page
  * aligned), to copy the length size data to daddr. Or, while doing normal DAX
  * write operation, dax_iomap_actor() might call this to do the copy of either
  * start or end unaligned address. In the latter case the rest of the copy of
  * aligned ranges is taken care by dax_iomap_actor() itself.
  */
 static int dax_iomap_cow_copy(loff_t pos, uint64_t length, size_t align_size,
         const struct iomap *srcmap, void *daddr)
 {
     loff_t head_off = pos & (align_size - 1);
     size_t size = ALIGN(head_off + length, align_size);
     loff_t end = pos + length;
     loff_t pg_end = round_up(end, align_size);
     bool copy_all = head_off == 0 && end == pg_end;
     void *saddr = 0;
     int ret = 0;
 
     ret = dax_iomap_direct_access(srcmap, pos, size, &saddr, NULL);
     if (ret)
         return ret;
 
     if (copy_all) {
         ret = copy_mc_to_kernel(daddr, saddr, length);
         return ret ? -EIO : 0;
     }
 
     /* Copy the head part of the range */
     if (head_off) {
         ret = copy_mc_to_kernel(daddr, saddr, head_off);
         if (ret)
             return -EIO;
     }
 
     /* Copy the tail part of the range */
     if (end < pg_end) {
         loff_t tail_off = head_off + length;
         loff_t tail_len = pg_end - end;
 
         ret = copy_mc_to_kernel(daddr + tail_off, saddr + tail_off,
                     tail_len);
         if (ret)
             return -EIO;
     }
     return 0;
 }
 
 /*
  * The user has performed a load from a hole in the file.  Allocating a new
  * page in the file would cause excessive storage usage for workloads with
  * sparse files.  Instead we insert a read-only mapping of the 4k zero page.
  * If this page is ever written to we will re-fault and change the mapping to
  * point to real DAX storage instead.
  */
 static vm_fault_t dax_load_hole(struct xa_state *xas, struct vm_fault *vmf,
         const struct iomap_iter *iter, void **entry)
 {
     struct inode *inode = iter->inode;
     unsigned long vaddr = vmf->address;
     pfn_t pfn = pfn_to_pfn_t(my_zero_pfn(vaddr));
     vm_fault_t ret;
 
     *entry = dax_insert_entry(xas, vmf, iter, *entry, pfn, DAX_ZERO_PAGE);
 
     ret = vmf_insert_mixed(vmf->vma, vaddr, pfn);
     trace_dax_load_hole(inode, vmf, ret);
     return ret;
 }
 
 #ifdef CONFIG_FS_DAX_PMD
 static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
         const struct iomap_iter *iter, void **entry)
 {
     struct address_space *mapping = vmf->vma->vm_file->f_mapping;
     unsigned long pmd_addr = vmf->address & PMD_MASK;
     struct vm_area_struct *vma = vmf->vma;
     struct inode *inode = mapping->host;
     pgtable_t pgtable = NULL;
     struct page *zero_page;
     spinlock_t *ptl;
     pmd_t pmd_entry;
     pfn_t pfn;
 
     zero_page = mm_get_huge_zero_page(vmf->vma->vm_mm);
 
     if (unlikely(!zero_page))
         goto fallback;
 
     pfn = page_to_pfn_t(zero_page);
     *entry = dax_insert_entry(xas, vmf, iter, *entry, pfn,
                   DAX_PMD | DAX_ZERO_PAGE);
 
     if (arch_needs_pgtable_deposit()) {
         pgtable = pte_alloc_one(vma->vm_mm);
         if (!pgtable)
             return VM_FAULT_OOM;
     }
 
     ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
     if (!pmd_none(*(vmf->pmd))) {
         spin_unlock(ptl);
         goto fallback;
     }
 
     if (pgtable) {
         pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
         mm_inc_nr_ptes(vma->vm_mm);
     }
     pmd_entry = mk_pmd(zero_page, vmf->vma->vm_page_prot);
     pmd_entry = pmd_mkhuge(pmd_entry);
     set_pmd_at(vmf->vma->vm_mm, pmd_addr, vmf->pmd, pmd_entry);
     spin_unlock(ptl);
     trace_dax_pmd_load_hole(inode, vmf, zero_page, *entry);
     return VM_FAULT_NOPAGE;
 
 fallback:
     if (pgtable)
         pte_free(vma->vm_mm, pgtable);
     trace_dax_pmd_load_hole_fallback(inode, vmf, zero_page, *entry);
     return VM_FAULT_FALLBACK;
 }
 #else
 static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
         const struct iomap_iter *iter, void **entry)
 {
     return VM_FAULT_FALLBACK;
 }
 #endif /* CONFIG_FS_DAX_PMD */
 
 static int dax_memzero(struct iomap_iter *iter, loff_t pos, size_t size)
 {
     const struct iomap *iomap = &iter->iomap;
     const struct iomap *srcmap = iomap_iter_srcmap(iter);
     unsigned offset = offset_in_page(pos);
     pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
     void *kaddr;
     long ret;
 
     ret = dax_direct_access(iomap->dax_dev, pgoff, 1, DAX_ACCESS, &kaddr,
                 NULL);
     if (ret < 0)
         return ret;
     memset(kaddr + offset, 0, size);
     if (srcmap->addr != iomap->addr) {
         ret = dax_iomap_cow_copy(pos, size, PAGE_SIZE, srcmap,
                      kaddr);
         if (ret < 0)
             return ret;
         dax_flush(iomap->dax_dev, kaddr, PAGE_SIZE);
     } else
         dax_flush(iomap->dax_dev, kaddr + offset, size);
     return ret;
 }
 
 static s64 dax_zero_iter(struct iomap_iter *iter, bool *did_zero)
 {
     const struct iomap *iomap = &iter->iomap;
     const struct iomap *srcmap = iomap_iter_srcmap(iter);
     loff_t pos = iter->pos;
     u64 length = iomap_length(iter);
     s64 written = 0;
 
     /* already zeroed?  we're done. */
     if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN)
         return length;
 
     do {
         unsigned offset = offset_in_page(pos);
         unsigned size = min_t(u64, PAGE_SIZE - offset, length);
         pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
         long rc;
         int id;
 
         id = dax_read_lock();
         if (IS_ALIGNED(pos, PAGE_SIZE) && size == PAGE_SIZE)
             rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
         else
             rc = dax_memzero(iter, pos, size);
         dax_read_unlock(id);
 
         if (rc < 0)
             return rc;
         pos += size;
         length -= size;
         written += size;
     } while (length > 0);
 
     if (did_zero)
         *did_zero = true;
     return written;
 }
 
 int dax_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
         const struct iomap_ops *ops)
 {
     struct iomap_iter iter = {
         .inode      = inode,
         .pos        = pos,
         .len        = len,
         .flags      = IOMAP_DAX | IOMAP_ZERO,
     };
     int ret;
 
     while ((ret = iomap_iter(&iter, ops)) > 0)
         iter.processed = dax_zero_iter(&iter, did_zero);
     return ret;
 }
 EXPORT_SYMBOL_GPL(dax_zero_range);
 
 int dax_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
         const struct iomap_ops *ops)
 {
     unsigned int blocksize = i_blocksize(inode);
     unsigned int off = pos & (blocksize - 1);
 
     /* Block boundary? Nothing to do */
     if (!off)
         return 0;
     return dax_zero_range(inode, pos, blocksize - off, did_zero, ops);
 }
 EXPORT_SYMBOL_GPL(dax_truncate_page);
 
 static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
         struct iov_iter *iter)
 {
     const struct iomap *iomap = &iomi->iomap;
     const struct iomap *srcmap = &iomi->srcmap;
     loff_t length = iomap_length(iomi);
     loff_t pos = iomi->pos;
     struct dax_device *dax_dev = iomap->dax_dev;
     loff_t end = pos + length, done = 0;
     bool write = iov_iter_rw(iter) == WRITE;
     ssize_t ret = 0;
     size_t xfer;
     int id;
 
     if (!write) {
         end = min(end, i_size_read(iomi->inode));
         if (pos >= end)
             return 0;
 
         if (iomap->type == IOMAP_HOLE || iomap->type == IOMAP_UNWRITTEN)
             return iov_iter_zero(min(length, end - pos), iter);
     }
 
     /*
      * In DAX mode, enforce either pure overwrites of written extents, or
      * writes to unwritten extents as part of a copy-on-write operation.
      */
     if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED &&
             !(iomap->flags & IOMAP_F_SHARED)))
         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(iomi->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);
         pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
         ssize_t map_len;
         bool recovery = false;
         void *kaddr;
 
         if (fatal_signal_pending(current)) {
             ret = -EINTR;
             break;
         }
 
         map_len = dax_direct_access(dax_dev, pgoff, PHYS_PFN(size),
                 DAX_ACCESS, &kaddr, NULL);
         if (map_len == -EIO && iov_iter_rw(iter) == WRITE) {
             map_len = dax_direct_access(dax_dev, pgoff,
                     PHYS_PFN(size), DAX_RECOVERY_WRITE,
                     &kaddr, NULL);
             if (map_len > 0)
                 recovery = true;
         }
         if (map_len < 0) {
             ret = map_len;
             break;
         }
 
         if (write &&
             srcmap->type != IOMAP_HOLE && srcmap->addr != iomap->addr) {
             ret = dax_iomap_cow_copy(pos, length, PAGE_SIZE, srcmap,
                          kaddr);
             if (ret)
                 break;
         }
 
         map_len = PFN_PHYS(map_len);
         kaddr += offset;
         map_len -= offset;
         if (map_len > end - pos)
             map_len = end - pos;
 
         if (recovery)
             xfer = dax_recovery_write(dax_dev, pgoff, kaddr,
                     map_len, iter);
         else if (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 iomap_iter iomi = {
         .inode      = iocb->ki_filp->f_mapping->host,
         .pos        = iocb->ki_pos,
         .len        = iov_iter_count(iter),
         .flags      = IOMAP_DAX,
     };
     loff_t done = 0;
     int ret;
 
     if (!iomi.len)
         return 0;
 
     if (iov_iter_rw(iter) == WRITE) {
         lockdep_assert_held_write(&iomi.inode->i_rwsem);
         iomi.flags |= IOMAP_WRITE;
     } else {
         lockdep_assert_held(&iomi.inode->i_rwsem);
     }
 
     if (iocb->ki_flags & IOCB_NOWAIT)
         iomi.flags |= IOMAP_NOWAIT;
 
     while ((ret = iomap_iter(&iomi, ops)) > 0)
         iomi.processed = dax_iomap_iter(&iomi, iter);
 
     done = iomi.pos - iocb->ki_pos;
     iocb->ki_pos = iomi.pos;
     return done ? done : ret;
 }
 EXPORT_SYMBOL_GPL(dax_iomap_rw);
 
 static vm_fault_t dax_fault_return(int error)
 {
     if (error == 0)
         return VM_FAULT_NOPAGE;
     return vmf_error(error);
 }
 
 /*
  * When handling a synchronous page fault and the inode need a fsync, we can
  * insert the PTE/PMD into page tables only after that fsync happened. Skip
  * insertion for now and return the pfn so that caller can insert it after the
  * fsync is done.
  */
 static vm_fault_t dax_fault_synchronous_pfnp(pfn_t *pfnp, pfn_t pfn)
 {
     if (WARN_ON_ONCE(!pfnp))
         return VM_FAULT_SIGBUS;
     *pfnp = pfn;
     return VM_FAULT_NEEDDSYNC;
 }
 
 static vm_fault_t dax_fault_cow_page(struct vm_fault *vmf,
         const struct iomap_iter *iter)
 {
     vm_fault_t ret;
     int error = 0;
 
     switch (iter->iomap.type) {
     case IOMAP_HOLE:
     case IOMAP_UNWRITTEN:
         clear_user_highpage(vmf->cow_page, vmf->address);
         break;
     case IOMAP_MAPPED:
         error = copy_cow_page_dax(vmf, iter);
         break;
     default:
         WARN_ON_ONCE(1);
         error = -EIO;
         break;
     }
 
     if (error)
         return dax_fault_return(error);
 
     __SetPageUptodate(vmf->cow_page);
     ret = finish_fault(vmf);
     if (!ret)
         return VM_FAULT_DONE_COW;
     return ret;
 }
 
 /**
  * dax_fault_iter - Common actor to handle pfn insertion in PTE/PMD fault.
  * @vmf:    vm fault instance
  * @iter:   iomap iter
  * @pfnp:   pfn to be returned
  * @xas:    the dax mapping tree of a file
  * @entry:  an unlocked dax entry to be inserted
  * @pmd:    distinguish whether it is a pmd fault
  */
 static vm_fault_t dax_fault_iter(struct vm_fault *vmf,
         const struct iomap_iter *iter, pfn_t *pfnp,
         struct xa_state *xas, void **entry, bool pmd)
 {
     const struct iomap *iomap = &iter->iomap;
     const struct iomap *srcmap = &iter->srcmap;
     size_t size = pmd ? PMD_SIZE : PAGE_SIZE;
     loff_t pos = (loff_t)xas->xa_index << PAGE_SHIFT;
     bool write = iter->flags & IOMAP_WRITE;
     unsigned long entry_flags = pmd ? DAX_PMD : 0;
     int err = 0;
     pfn_t pfn;
     void *kaddr;
 
     if (!pmd && vmf->cow_page)
         return dax_fault_cow_page(vmf, iter);
 
     /* if we are reading UNWRITTEN and HOLE, return a hole. */
     if (!write &&
         (iomap->type == IOMAP_UNWRITTEN || iomap->type == IOMAP_HOLE)) {
         if (!pmd)
             return dax_load_hole(xas, vmf, iter, entry);
         return dax_pmd_load_hole(xas, vmf, iter, entry);
     }
 
     if (iomap->type != IOMAP_MAPPED && !(iomap->flags & IOMAP_F_SHARED)) {
         WARN_ON_ONCE(1);
         return pmd ? VM_FAULT_FALLBACK : VM_FAULT_SIGBUS;
     }
 
     err = dax_iomap_direct_access(iomap, pos, size, &kaddr, &pfn);
     if (err)
         return pmd ? VM_FAULT_FALLBACK : dax_fault_return(err);
 
     *entry = dax_insert_entry(xas, vmf, iter, *entry, pfn, entry_flags);
 
     if (write &&
         srcmap->type != IOMAP_HOLE && srcmap->addr != iomap->addr) {
         err = dax_iomap_cow_copy(pos, size, size, srcmap, kaddr);
         if (err)
             return dax_fault_return(err);
     }
 
     if (dax_fault_is_synchronous(iter, vmf->vma))
         return dax_fault_synchronous_pfnp(pfnp, pfn);
 
     /* insert PMD pfn */
     if (pmd)
         return vmf_insert_pfn_pmd(vmf, pfn, write);
 
     /* insert PTE pfn */
     if (write)
         return vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
     return vmf_insert_mixed(vmf->vma, vmf->address, pfn);
 }
 
 static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
                    int *iomap_errp, const struct iomap_ops *ops)
 {
     struct address_space *mapping = vmf->vma->vm_file->f_mapping;
     XA_STATE(xas, &mapping->i_pages, vmf->pgoff);
     struct iomap_iter iter = {
         .inode      = mapping->host,
         .pos        = (loff_t)vmf->pgoff << PAGE_SHIFT,
         .len        = PAGE_SIZE,
         .flags      = IOMAP_DAX | IOMAP_FAULT,
     };
     vm_fault_t ret = 0;
     void *entry;
     int error;
 
     trace_dax_pte_fault(iter.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 (iter.pos >= i_size_read(iter.inode)) {
         ret = VM_FAULT_SIGBUS;
         goto out;
     }
 
     if ((vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page)
         iter.flags |= IOMAP_WRITE;
 
     entry = grab_mapping_entry(&xas, mapping, 0);
     if (xa_is_internal(entry)) {
         ret = xa_to_internal(entry);
         goto out;
     }
 
     /*
      * It is possible, particularly with mixed reads & writes to private
      * mappings, that we have raced with a PMD fault that overlaps with
      * the PTE we need to set up.  If so just return and the fault will be
      * retried.
      */
     if (pmd_trans_huge(*vmf->pmd) || pmd_devmap(*vmf->pmd)) {
         ret = VM_FAULT_NOPAGE;
         goto unlock_entry;
     }
 
     while ((error = iomap_iter(&iter, ops)) > 0) {
         if (WARN_ON_ONCE(iomap_length(&iter) < PAGE_SIZE)) {
             iter.processed = -EIO;  /* fs corruption? */
             continue;
         }
 
         ret = dax_fault_iter(vmf, &iter, pfnp, &xas, &entry, false);
         if (ret != VM_FAULT_SIGBUS &&
             (iter.iomap.flags & IOMAP_F_NEW)) {
             count_vm_event(PGMAJFAULT);
             count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
             ret |= VM_FAULT_MAJOR;
         }
 
         if (!(ret & VM_FAULT_ERROR))
             iter.processed = PAGE_SIZE;
     }
 
     if (iomap_errp)
         *iomap_errp = error;
     if (!ret && error)
         ret = dax_fault_return(error);
 
 unlock_entry:
     dax_unlock_entry(&xas, entry);
 out:
     trace_dax_pte_fault_done(iter.inode, vmf, ret);
     return ret;
 }
 
 #ifdef CONFIG_FS_DAX_PMD
 static bool dax_fault_check_fallback(struct vm_fault *vmf, struct xa_state *xas,
         pgoff_t max_pgoff)
 {
     unsigned long pmd_addr = vmf->address & PMD_MASK;
     bool write = vmf->flags & FAULT_FLAG_WRITE;
 
     /*
      * 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 page cache.
      */
     if ((vmf->pgoff & PG_PMD_COLOUR) !=
         ((vmf->address >> PAGE_SHIFT) & PG_PMD_COLOUR))
         return true;
 
     /* Fall back to PTEs if we're going to COW */
     if (write && !(vmf->vma->vm_flags & VM_SHARED))
         return true;
 
     /* If the PMD would extend outside the VMA */
     if (pmd_addr < vmf->vma->vm_start)
         return true;
     if ((pmd_addr + PMD_SIZE) > vmf->vma->vm_end)
         return true;
 
     /* If the PMD would extend beyond the file size */
     if ((xas->xa_index | PG_PMD_COLOUR) >= max_pgoff)
         return true;
 
     return false;
 }
 
 static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
                    const struct iomap_ops *ops)
 {
     struct address_space *mapping = vmf->vma->vm_file->f_mapping;
     XA_STATE_ORDER(xas, &mapping->i_pages, vmf->pgoff, PMD_ORDER);
     struct iomap_iter iter = {
         .inode      = mapping->host,
         .len        = PMD_SIZE,
         .flags      = IOMAP_DAX | IOMAP_FAULT,
     };
     vm_fault_t ret = VM_FAULT_FALLBACK;
     pgoff_t max_pgoff;
     void *entry;
     int error;
 
     if (vmf->flags & FAULT_FLAG_WRITE)
         iter.flags |= IOMAP_WRITE;
 
     /*
      * 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.
      */
     max_pgoff = DIV_ROUND_UP(i_size_read(iter.inode), PAGE_SIZE);
 
     trace_dax_pmd_fault(iter.inode, vmf, max_pgoff, 0);
 
     if (xas.xa_index >= max_pgoff) {
         ret = VM_FAULT_SIGBUS;
         goto out;
     }
 
     if (dax_fault_check_fallback(vmf, &xas, max_pgoff))
         goto fallback;
 
     /*
      * grab_mapping_entry() will make sure we get an empty PMD entry,
      * a zero PMD entry or a DAX PMD.  If it can't (because a PTE
      * entry is already in the array, for instance), it will return
      * VM_FAULT_FALLBACK.
      */
     entry = grab_mapping_entry(&xas, mapping, PMD_ORDER);
     if (xa_is_internal(entry)) {
         ret = xa_to_internal(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)) {
         ret = 0;
         goto unlock_entry;
     }
 
     iter.pos = (loff_t)xas.xa_index << PAGE_SHIFT;
     while ((error = iomap_iter(&iter, ops)) > 0) {
         if (iomap_length(&iter) < PMD_SIZE)
             continue; /* actually breaks out of the loop */
 
         ret = dax_fault_iter(vmf, &iter, pfnp, &xas, &entry, true);
         if (ret != VM_FAULT_FALLBACK)
             iter.processed = PMD_SIZE;
     }
 
 unlock_entry:
     dax_unlock_entry(&xas, entry);
 fallback:
     if (ret == VM_FAULT_FALLBACK) {
         split_huge_pmd(vmf->vma, vmf->pmd, vmf->address);
         count_vm_event(THP_FAULT_FALLBACK);
     }
 out:
     trace_dax_pmd_fault_done(iter.inode, vmf, max_pgoff, ret);
     return ret;
 }
 #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
  * @pfn: PFN to insert
  * @order: Order of entry to insert.
  *
  * This function inserts a writeable PTE or PMD entry into the page tables
  * for an mmaped DAX file.  It also marks the page cache entry as dirty.
  */
 static vm_fault_t
 dax_insert_pfn_mkwrite(struct vm_fault *vmf, pfn_t pfn, unsigned int order)
 {
     struct address_space *mapping = vmf->vma->vm_file->f_mapping;
     XA_STATE_ORDER(xas, &mapping->i_pages, vmf->pgoff, order);
     void *entry;
     vm_fault_t ret;
 
     xas_lock_irq(&xas);
     entry = get_unlocked_entry(&xas, order);
     /* Did we race with someone splitting entry or so? */
     if (!entry || dax_is_conflict(entry) ||
         (order == 0 && !dax_is_pte_entry(entry))) {
         put_unlocked_entry(&xas, entry, WAKE_NEXT);
         xas_unlock_irq(&xas);
         trace_dax_insert_pfn_mkwrite_no_entry(mapping->host, vmf,
                               VM_FAULT_NOPAGE);
         return VM_FAULT_NOPAGE;
     }
     xas_set_mark(&xas, PAGECACHE_TAG_DIRTY);
     dax_lock_entry(&xas, entry);
     xas_unlock_irq(&xas);
     if (order == 0)
         ret = vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
 #ifdef CONFIG_FS_DAX_PMD
     else if (order == PMD_ORDER)
         ret = vmf_insert_pfn_pmd(vmf, pfn, FAULT_FLAG_WRITE);
 #endif
     else
         ret = VM_FAULT_FALLBACK;
     dax_unlock_entry(&xas, entry);
     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;
     unsigned int order = pe_order(pe_size);
     size_t len = PAGE_SIZE << order;
 
     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, pfn, order);
 }
 EXPORT_SYMBOL_GPL(dax_finish_sync_fault);
 
 static loff_t dax_range_compare_iter(struct iomap_iter *it_src,
         struct iomap_iter *it_dest, u64 len, bool *same)
 {
     const struct iomap *smap = &it_src->iomap;
     const struct iomap *dmap = &it_dest->iomap;
     loff_t pos1 = it_src->pos, pos2 = it_dest->pos;
     void *saddr, *daddr;
     int id, ret;
 
     len = min(len, min(smap->length, dmap->length));
 
     if (smap->type == IOMAP_HOLE && dmap->type == IOMAP_HOLE) {
         *same = true;
         return len;
     }
 
     if (smap->type == IOMAP_HOLE || dmap->type == IOMAP_HOLE) {
         *same = false;
         return 0;
     }
 
     id = dax_read_lock();
     ret = dax_iomap_direct_access(smap, pos1, ALIGN(pos1 + len, PAGE_SIZE),
                       &saddr, NULL);
     if (ret < 0)
         goto out_unlock;
 
     ret = dax_iomap_direct_access(dmap, pos2, ALIGN(pos2 + len, PAGE_SIZE),
                       &daddr, NULL);
     if (ret < 0)
         goto out_unlock;
 
     *same = !memcmp(saddr, daddr, len);
     if (!*same)
         len = 0;
     dax_read_unlock(id);
     return len;
 
 out_unlock:
     dax_read_unlock(id);
     return -EIO;
 }
 
 int dax_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
         struct inode *dst, loff_t dstoff, loff_t len, bool *same,
         const struct iomap_ops *ops)
 {
     struct iomap_iter src_iter = {
         .inode      = src,
         .pos        = srcoff,
         .len        = len,
         .flags      = IOMAP_DAX,
     };
     struct iomap_iter dst_iter = {
         .inode      = dst,
         .pos        = dstoff,
         .len        = len,
         .flags      = IOMAP_DAX,
     };
     int ret;
 
     while ((ret = iomap_iter(&src_iter, ops)) > 0) {
         while ((ret = iomap_iter(&dst_iter, ops)) > 0) {
             dst_iter.processed = dax_range_compare_iter(&src_iter,
                         &dst_iter, len, same);
         }
         if (ret <= 0)
             src_iter.processed = ret;
     }
     return ret;
 }
 
 int dax_remap_file_range_prep(struct file *file_in, loff_t pos_in,
                   struct file *file_out, loff_t pos_out,
                   loff_t *len, unsigned int remap_flags,
                   const struct iomap_ops *ops)
 {
     return __generic_remap_file_range_prep(file_in, pos_in, file_out,
                            pos_out, len, remap_flags, ops);
 }
 EXPORT_SYMBOL_GPL(dax_remap_file_range_prep);

This page was automatically generated by the 2.1.0 LXR engine. The LXR team