1 files changed, 341 insertions, 37 deletions

diff --git a/fs/dax.c b/fs/dax.c
index 0582c7c2ae40..281e91a63367 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -76,6 +76,26 @@ static void dax_unmap_atomic(struct block_device *bdev,
         blk_queue_exit(bdev->bd_queue);
 }
 
+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_HZP;
+}
+
+static int dax_is_empty_entry(void *entry)
+{
+        return (unsigned long)entry & RADIX_DAX_EMPTY;
+}
+
 struct page *read_dax_sector(struct block_device *bdev, sector_t n)
 {
         struct page *page = alloc_pages(GFP_KERNEL, 0);
@@ -281,7 +301,7 @@ static wait_queue_head_t *dax_entry_waitqueue(struct address_space *mapping,
          * 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 (RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
+        if (dax_is_pmd_entry(entry))
                 index &= ~((1UL << (PMD_SHIFT - PAGE_SHIFT)) - 1);
 
         key->mapping = mapping;
@@ -413,36 +433,116 @@ static void put_unlocked_mapping_entry(struct address_space *mapping,
  * radix tree entry locked. If the radix tree doesn't contain given index,
  * create 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 (either zero pages or DAX 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)
+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:
         spin_lock_irq(&mapping->tree_lock);
         entry = get_unlocked_mapping_entry(mapping, index, &slot);
+
+        if (entry) {
+                if (size_flag & RADIX_DAX_PMD) {
+                        if (!radix_tree_exceptional_entry(entry) ||
+                            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 (radix_tree_exceptional_entry(entry) &&
+                            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) {
+        if (!entry || pmd_downgrade) {
                 int err;
 
+                if (pmd_downgrade) {
+                        /*
+                         * Make sure 'entry' remains valid while we drop
+                         * mapping->tree_lock.
+                         */
+                        entry = lock_slot(mapping, slot);
+                }
+
                 spin_unlock_irq(&mapping->tree_lock);
                 err = radix_tree_preload(
                                 mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM);
-                if (err)
+                if (err) {
+                        if (pmd_downgrade)
+                                put_locked_mapping_entry(mapping, index, entry);
                         return ERR_PTR(err);
-                entry = (void *)(RADIX_TREE_EXCEPTIONAL_ENTRY |
-                               RADIX_DAX_ENTRY_LOCK);
+                }
+
+                /*
+                 * 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_range(mapping,
+                                (index << PAGE_SHIFT) & PMD_MASK, PMD_SIZE, 0);
+
                 spin_lock_irq(&mapping->tree_lock);
-                err = radix_tree_insert(&mapping->page_tree, index, entry);
+
+                if (pmd_downgrade) {
+                        radix_tree_delete(&mapping->page_tree, 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->page_tree, index,
+                                dax_radix_order(entry), entry);
                 radix_tree_preload_end();
                 if (err) {
                         spin_unlock_irq(&mapping->tree_lock);
-                        /* Someone already created the entry? */
-                        if (err == -EEXIST)
+                        /*
+                         * Someone already created the entry?  This is a
+                         * normal failure when inserting PMDs in a range
+                         * that already contains PTEs.  In that case we want
+                         * to return -EEXIST immediately.
+                         */
+                        if (err == -EEXIST && !(size_flag & RADIX_DAX_PMD))
                                 goto restart;
+                        /*
+                         * Our insertion of a DAX PMD entry failed, most
+                         * likely because 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. */
@@ -466,6 +566,7 @@ restart:
                 return page;
         }
         entry = lock_slot(mapping, slot);
+ out_unlock:
         spin_unlock_irq(&mapping->tree_lock);
         return entry;
 }
@@ -473,9 +574,9 @@ restart:
 /*
  * We do not necessarily hold the mapping->tree_lock when we call this
  * function so it is possible that 'entry' is no longer a valid item in the
- * radix tree.  This is okay, though, because all we really need to do is to
- * find the correct waitqueue where tasks might be sleeping waiting for that
- * old 'entry' and wake them.
+ * radix tree.  This is okay because all we really need to do is to find the
+ * correct waitqueue where tasks might be waiting for that old 'entry' and
+ * wake them.
  */
 void dax_wake_mapping_entry_waiter(struct address_space *mapping,
                 pgoff_t index, void *entry, bool wake_all)
@@ -588,11 +689,17 @@ static int copy_user_dax(struct block_device *bdev, sector_t sector, size_t size
         return 0;
 }
 
-#define DAX_PMD_INDEX(page_index) (page_index & (PMD_MASK >> PAGE_SHIFT))
-
+/*
+ * 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, sector_t sector)
+                                      void *entry, sector_t sector,
+                                      unsigned long flags)
 {
         struct radix_tree_root *page_tree = &mapping->page_tree;
         int error = 0;
@@ -615,22 +722,35 @@ static void *dax_insert_mapping_entry(struct address_space *mapping,
                 error = radix_tree_preload(vmf->gfp_mask & ~__GFP_HIGHMEM);
                 if (error)
                         return ERR_PTR(error);
+        } else if (dax_is_zero_entry(entry) && !(flags & RADIX_DAX_HZP)) {
+                /* replacing huge zero page with PMD block mapping */
+                unmap_mapping_range(mapping,
+                        (vmf->pgoff << PAGE_SHIFT) & PMD_MASK, PMD_SIZE, 0);
         }
 
         spin_lock_irq(&mapping->tree_lock);
-        new_entry = (void *)((unsigned long)RADIX_DAX_ENTRY(sector, false) |
-                       RADIX_DAX_ENTRY_LOCK);
+        new_entry = dax_radix_locked_entry(sector, flags);
+
         if (hole_fill) {
                 __delete_from_page_cache(entry, NULL);
                 /* Drop pagecache reference */
                 put_page(entry);
-                error = radix_tree_insert(page_tree, index, new_entry);
+                error = __radix_tree_insert(page_tree, index,
+                                dax_radix_order(new_entry), new_entry);
                 if (error) {
                         new_entry = ERR_PTR(error);
                         goto unlock;
                 }
                 mapping->nrexceptional++;
-        } else {
+        } else 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.
+                 */
                 void **slot;
                 void *ret;
 
@@ -660,7 +780,6 @@ static int dax_writeback_one(struct block_device *bdev,
                 struct address_space *mapping, pgoff_t index, void *entry)
 {
         struct radix_tree_root *page_tree = &mapping->page_tree;
-        int type = RADIX_DAX_TYPE(entry);
         struct radix_tree_node *node;
         struct blk_dax_ctl dax;
         void **slot;
@@ -681,13 +800,21 @@ static int dax_writeback_one(struct block_device *bdev,
         if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
                 goto unlock;
 
-        if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD)) {
+        if (WARN_ON_ONCE(dax_is_empty_entry(entry) ||
+                                dax_is_zero_entry(entry))) {
                 ret = -EIO;
                 goto unlock;
         }
 
-        dax.sector = RADIX_DAX_SECTOR(entry);
-        dax.size = (type == RADIX_DAX_PMD ? PMD_SIZE : PAGE_SIZE);
+        /*
+         * 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 sector we pull from
+         * 'entry'.  This allows us to flush for PMD_SIZE and not have to
+         * worry about partial PMD writebacks.
+         */
+        dax.sector = dax_radix_sector(entry);
+        dax.size = PAGE_SIZE << dax_radix_order(entry);
         spin_unlock_irq(&mapping->tree_lock);
 
         /*
@@ -726,12 +853,11 @@ 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, pmd_index;
+        pgoff_t start_index, end_index;
         pgoff_t indices[PAGEVEC_SIZE];
         struct pagevec pvec;
         bool done = false;
         int i, ret = 0;
-        void *entry;
 
         if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))
                 return -EIO;
@@ -741,15 +867,6 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 
         start_index = wbc->range_start >> PAGE_SHIFT;
         end_index = wbc->range_end >> PAGE_SHIFT;
-        pmd_index = DAX_PMD_INDEX(start_index);
-
-        rcu_read_lock();
-        entry = radix_tree_lookup(&mapping->page_tree, pmd_index);
-        rcu_read_unlock();
-
-        /* see if the start of our range is covered by a PMD entry */
-        if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
-                start_index = pmd_index;
 
         tag_pages_for_writeback(mapping, start_index, end_index);
 
@@ -794,7 +911,7 @@ static int dax_insert_mapping(struct address_space *mapping,
                 return PTR_ERR(dax.addr);
         dax_unmap_atomic(bdev, &dax);
 
-        ret = dax_insert_mapping_entry(mapping, vmf, entry, dax.sector);
+        ret = dax_insert_mapping_entry(mapping, vmf, entry, dax.sector, 0);
         if (IS_ERR(ret))
                 return PTR_ERR(ret);
         *entryp = ret;
@@ -841,7 +958,7 @@ int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
         bh.b_bdev = inode->i_sb->s_bdev;
         bh.b_size = PAGE_SIZE;
 
-        entry = grab_mapping_entry(mapping, vmf->pgoff);
+        entry = grab_mapping_entry(mapping, vmf->pgoff, 0);
         if (IS_ERR(entry)) {
                 error = PTR_ERR(entry);
                 goto out;
@@ -1162,7 +1279,7 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
         if (pos >= i_size_read(inode))
                 return VM_FAULT_SIGBUS;
 
-        entry = grab_mapping_entry(mapping, vmf->pgoff);
+        entry = grab_mapping_entry(mapping, vmf->pgoff, 0);
         if (IS_ERR(entry)) {
                 error = PTR_ERR(entry);
                 goto out;
@@ -1264,4 +1381,191 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
         return VM_FAULT_NOPAGE | major;
 }
 EXPORT_SYMBOL_GPL(dax_iomap_fault);
+
+#ifdef CONFIG_FS_DAX_PMD
+/*
+ * The 'colour' (ie low bits) within a PMD of a page offset.  This comes up
+ * more often than one might expect in the below functions.
+ */
+#define PG_PMD_COLOUR   ((PMD_SIZE >> PAGE_SHIFT) - 1)
+
+static int dax_pmd_insert_mapping(struct vm_area_struct *vma, pmd_t *pmd,
+                struct vm_fault *vmf, unsigned long address,
+                struct iomap *iomap, loff_t pos, bool write, void **entryp)
+{
+        struct address_space *mapping = vma->vm_file->f_mapping;
+        struct block_device *bdev = iomap->bdev;
+        struct blk_dax_ctl dax = {
+                .sector = dax_iomap_sector(iomap, pos),
+                .size = PMD_SIZE,
+        };
+        long length = dax_map_atomic(bdev, &dax);
+        void *ret;
+
+        if (length < 0) /* dax_map_atomic() failed */
+                return VM_FAULT_FALLBACK;
+        if (length < PMD_SIZE)
+                goto unmap_fallback;
+        if (pfn_t_to_pfn(dax.pfn) & PG_PMD_COLOUR)
+                goto unmap_fallback;
+        if (!pfn_t_devmap(dax.pfn))
+                goto unmap_fallback;
+
+        dax_unmap_atomic(bdev, &dax);
+
+        ret = dax_insert_mapping_entry(mapping, vmf, *entryp, dax.sector,
+                        RADIX_DAX_PMD);
+        if (IS_ERR(ret))
+                return VM_FAULT_FALLBACK;
+        *entryp = ret;
+
+        return vmf_insert_pfn_pmd(vma, address, pmd, dax.pfn, write);
+
+ unmap_fallback:
+        dax_unmap_atomic(bdev, &dax);
+        return VM_FAULT_FALLBACK;
+}
+
+static int dax_pmd_load_hole(struct vm_area_struct *vma, pmd_t *pmd,
+                struct vm_fault *vmf, unsigned long address,
+                struct iomap *iomap, void **entryp)
+{
+        struct address_space *mapping = vma->vm_file->f_mapping;
+        unsigned long pmd_addr = address & PMD_MASK;
+        struct page *zero_page;
+        spinlock_t *ptl;
+        pmd_t pmd_entry;
+        void *ret;
+
+        zero_page = mm_get_huge_zero_page(vma->vm_mm);
+
+        if (unlikely(!zero_page))
+                return VM_FAULT_FALLBACK;
+
+        ret = dax_insert_mapping_entry(mapping, vmf, *entryp, 0,
+                        RADIX_DAX_PMD | RADIX_DAX_HZP);
+        if (IS_ERR(ret))
+                return VM_FAULT_FALLBACK;
+        *entryp = ret;
+
+        ptl = pmd_lock(vma->vm_mm, pmd);
+        if (!pmd_none(*pmd)) {
+                spin_unlock(ptl);
+                return VM_FAULT_FALLBACK;
+        }
+
+        pmd_entry = mk_pmd(zero_page, vma->vm_page_prot);
+        pmd_entry = pmd_mkhuge(pmd_entry);
+        set_pmd_at(vma->vm_mm, pmd_addr, pmd, pmd_entry);
+        spin_unlock(ptl);
+        return VM_FAULT_NOPAGE;
+}
+
+int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address,
+                pmd_t *pmd, unsigned int flags, struct iomap_ops *ops)
+{
+        struct address_space *mapping = vma->vm_file->f_mapping;
+        unsigned long pmd_addr = address & PMD_MASK;
+        bool write = flags & FAULT_FLAG_WRITE;
+        unsigned int iomap_flags = write ? IOMAP_WRITE : 0;
+        struct inode *inode = mapping->host;
+        int result = VM_FAULT_FALLBACK;
+        struct iomap iomap = { 0 };
+        pgoff_t max_pgoff, pgoff;
+        struct vm_fault vmf;
+        void *entry;
+        loff_t pos;
+        int error;
+
+        /* 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;
+
+        /*
+         * 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 = (i_size_read(inode) - 1) >> PAGE_SHIFT;
+
+        if (pgoff > max_pgoff)
+                return VM_FAULT_SIGBUS;
+
+        /* 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 2M empty entry, a DAX
+         * PMD or a HZP entry.  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;
+
+        /*
+         * 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;
+
+        vmf.pgoff = pgoff;
+        vmf.flags = flags;
+        vmf.gfp_mask = mapping_gfp_mask(mapping) | __GFP_IO;
+
+        switch (iomap.type) {
+        case IOMAP_MAPPED:
+                result = dax_pmd_insert_mapping(vma, pmd, &vmf, address,
+                                &iomap, pos, write, &entry);
+                break;
+        case IOMAP_UNWRITTEN:
+        case IOMAP_HOLE:
+                if (WARN_ON_ONCE(write))
+                        goto finish_iomap;
+                result = dax_pmd_load_hole(vma, pmd, &vmf, address, &iomap,
+                                &entry);
+                break;
+        default:
+                WARN_ON_ONCE(1);
+                break;
+        }
+
+ finish_iomap:
+        if (ops->iomap_end) {
+                if (result == VM_FAULT_FALLBACK) {
+                        ops->iomap_end(inode, pos, PMD_SIZE, 0, iomap_flags,
+                                        &iomap);
+                } else {
+                        error = ops->iomap_end(inode, pos, PMD_SIZE, PMD_SIZE,
+                                        iomap_flags, &iomap);
+                        if (error)
+                                result = VM_FAULT_FALLBACK;
+                }
+        }
+ unlock_entry:
+        put_locked_mapping_entry(mapping, pgoff, entry);
+ fallback:
+        if (result == VM_FAULT_FALLBACK) {
+                split_huge_pmd(vma, pmd, address);
+                count_vm_event(THP_FAULT_FALLBACK);
+        }
+        return result;
+}
+EXPORT_SYMBOL_GPL(dax_iomap_pmd_fault);
+#endif /* CONFIG_FS_DAX_PMD */
 #endif /* CONFIG_FS_IOMAP */