1 files changed, 275 insertions, 303 deletions

diff --git a/fs/dax.c b/fs/dax.c
index 99b4e78d888f..4e3e5a283a91 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1005,12 +1005,12 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 }
 EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
 
-static sector_t dax_iomap_sector(struct iomap *iomap, loff_t pos)
+static sector_t dax_iomap_sector(const 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,
+static int dax_iomap_pfn(const struct iomap *iomap, loff_t pos, size_t size,
 			 pfn_t *pfnp)
 {
 	const sector_t sector = dax_iomap_sector(iomap, pos);
@@ -1066,6 +1066,66 @@ static vm_fault_t dax_load_hole(struct xa_state *xas,
 	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 *iomap, void **entry)
+{
+	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
+	unsigned long pmd_addr = vmf->address & PMD_MASK;
+	struct vm_area_struct *vma = vmf->vma;
+	struct inode *inode = mapping->host;
+	pgtable_t pgtable = NULL;
+	struct page *zero_page;
+	spinlock_t *ptl;
+	pmd_t pmd_entry;
+	pfn_t pfn;
+
+	zero_page = mm_get_huge_zero_page(vmf->vma->vm_mm);
+
+	if (unlikely(!zero_page))
+		goto fallback;
+
+	pfn = page_to_pfn_t(zero_page);
+	*entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
+			DAX_PMD | DAX_ZERO_PAGE, false);
+
+	if (arch_needs_pgtable_deposit()) {
+		pgtable = pte_alloc_one(vma->vm_mm);
+		if (!pgtable)
+			return VM_FAULT_OOM;
+	}
+
+	ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
+	if (!pmd_none(*(vmf->pmd))) {
+		spin_unlock(ptl);
+		goto fallback;
+	}
+
+	if (pgtable) {
+		pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
+		mm_inc_nr_ptes(vma->vm_mm);
+	}
+	pmd_entry = mk_pmd(zero_page, vmf->vma->vm_page_prot);
+	pmd_entry = pmd_mkhuge(pmd_entry);
+	set_pmd_at(vmf->vma->vm_mm, pmd_addr, vmf->pmd, pmd_entry);
+	spin_unlock(ptl);
+	trace_dax_pmd_load_hole(inode, vmf, zero_page, *entry);
+	return VM_FAULT_NOPAGE;
+
+fallback:
+	if (pgtable)
+		pte_free(vma->vm_mm, pgtable);
+	trace_dax_pmd_load_hole_fallback(inode, vmf, zero_page, *entry);
+	return VM_FAULT_FALLBACK;
+}
+#else
+static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
+		const struct iomap *iomap, void **entry)
+{
+	return VM_FAULT_FALLBACK;
+}
+#endif /* CONFIG_FS_DAX_PMD */
+
 s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
 {
 	sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
@@ -1103,20 +1163,21 @@ s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
 	return size;
 }
 
-static loff_t
-dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
-		struct iomap *iomap, struct iomap *srcmap)
+static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
+		struct iov_iter *iter)
 {
+	const struct iomap *iomap = &iomi->iomap;
+	loff_t length = iomap_length(iomi);
+	loff_t pos = iomi->pos;
 	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));
+		end = min(end, i_size_read(iomi->inode));
 		if (pos >= end)
 			return 0;
 
@@ -1133,7 +1194,7 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 	 * written by write(2) is visible in mmap.
 	 */
 	if (iomap->flags & IOMAP_F_NEW) {
-		invalidate_inode_pages2_range(inode->i_mapping,
+		invalidate_inode_pages2_range(iomi->inode->i_mapping,
 					      pos >> PAGE_SHIFT,
 					      (end - 1) >> PAGE_SHIFT);
 	}
@@ -1209,31 +1270,29 @@ 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;
+	struct iomap_iter iomi = {
+		.inode		= iocb->ki_filp->f_mapping->host,
+		.pos		= iocb->ki_pos,
+		.len		= iov_iter_count(iter),
+	};
+	loff_t done = 0;
+	int ret;
 
 	if (iov_iter_rw(iter) == WRITE) {
-		lockdep_assert_held_write(&inode->i_rwsem);
-		flags |= IOMAP_WRITE;
+		lockdep_assert_held_write(&iomi.inode->i_rwsem);
+		iomi.flags |= IOMAP_WRITE;
 	} else {
-		lockdep_assert_held(&inode->i_rwsem);
+		lockdep_assert_held(&iomi.inode->i_rwsem);
 	}
 
 	if (iocb->ki_flags & IOCB_NOWAIT)
-		flags |= IOMAP_NOWAIT;
+		iomi.flags |= IOMAP_NOWAIT;
 
-	while (iov_iter_count(iter)) {
-		ret = iomap_apply(inode, pos, iov_iter_count(iter), flags, ops,
-				iter, dax_iomap_actor);
-		if (ret <= 0)
-			break;
-		pos += ret;
-		done += ret;
-	}
+	while ((ret = iomap_iter(&iomi, ops)) > 0)
+		iomi.processed = dax_iomap_iter(&iomi, iter);
 
-	iocb->ki_pos += done;
+	done = iomi.pos - iocb->ki_pos;
+	iocb->ki_pos = iomi.pos;
 	return done ? done : ret;
 }
 EXPORT_SYMBOL_GPL(dax_iomap_rw);
@@ -1250,44 +1309,146 @@ static vm_fault_t dax_fault_return(int error)
  * 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)
+		struct vm_area_struct *vma, const struct iomap *iomap)
 {
 	return (flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC)
 		&& (iomap->flags & IOMAP_F_DIRTY);
 }
 
+/*
+ * 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)
+{
+	sector_t sector = dax_iomap_sector(&iter->iomap, iter->pos);
+	unsigned long vaddr = vmf->address;
+	vm_fault_t ret;
+	int error = 0;
+
+	switch (iter->iomap.type) {
+	case IOMAP_HOLE:
+	case IOMAP_UNWRITTEN:
+		clear_user_highpage(vmf->cow_page, vaddr);
+		break;
+	case IOMAP_MAPPED:
+		error = copy_cow_page_dax(iter->iomap.bdev, iter->iomap.dax_dev,
+					  sector, vmf->cow_page, vaddr);
+		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)
+{
+	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
+	const struct iomap *iomap = &iter->iomap;
+	size_t size = pmd ? PMD_SIZE : PAGE_SIZE;
+	loff_t pos = (loff_t)xas->xa_index << PAGE_SHIFT;
+	bool write = vmf->flags & FAULT_FLAG_WRITE;
+	bool sync = dax_fault_is_synchronous(iter->flags, vmf->vma, iomap);
+	unsigned long entry_flags = pmd ? DAX_PMD : 0;
+	int err = 0;
+	pfn_t pfn;
+
+	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, mapping, entry, vmf);
+		return dax_pmd_load_hole(xas, vmf, iomap, entry);
+	}
+
+	if (iomap->type != IOMAP_MAPPED) {
+		WARN_ON_ONCE(1);
+		return pmd ? VM_FAULT_FALLBACK : VM_FAULT_SIGBUS;
+	}
+
+	err = dax_iomap_pfn(&iter->iomap, pos, size, &pfn);
+	if (err)
+		return pmd ? VM_FAULT_FALLBACK : dax_fault_return(err);
+
+	*entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn, entry_flags,
+				  write && !sync);
+
+	if (sync)
+		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 vm_area_struct *vma = vmf->vma;
-	struct address_space *mapping = vma->vm_file->f_mapping;
+	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
 	XA_STATE(xas, &mapping->i_pages, vmf->pgoff);
-	struct inode *inode = mapping->host;
-	unsigned long vaddr = vmf->address;
-	loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;
-	struct iomap iomap = { .type = IOMAP_HOLE };
-	struct iomap srcmap = { .type = IOMAP_HOLE };
-	unsigned flags = IOMAP_FAULT;
-	int error, major = 0;
-	bool write = vmf->flags & FAULT_FLAG_WRITE;
-	bool sync;
+	struct iomap_iter iter = {
+		.inode		= mapping->host,
+		.pos		= (loff_t)vmf->pgoff << PAGE_SHIFT,
+		.len		= PAGE_SIZE,
+		.flags		= IOMAP_FAULT,
+	};
 	vm_fault_t ret = 0;
 	void *entry;
-	pfn_t pfn;
+	int error;
 
-	trace_dax_pte_fault(inode, vmf, ret);
+	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 (pos >= i_size_read(inode)) {
+	if (iter.pos >= i_size_read(iter.inode)) {
 		ret = VM_FAULT_SIGBUS;
 		goto out;
 	}
 
-	if (write && !vmf->cow_page)
-		flags |= IOMAP_WRITE;
+	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)) {
@@ -1306,234 +1467,103 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
 		goto unlock_entry;
 	}
 
-	/*
-	 * Note that we don't bother to use iomap_apply here: DAX required
-	 * the file system block size to be equal the page size, which means
-	 * that we never have to deal with more than a single extent here.
-	 */
-	error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap, &srcmap);
-	if (iomap_errp)
-		*iomap_errp = error;
-	if (error) {
-		ret = dax_fault_return(error);
-		goto unlock_entry;
-	}
-	if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) {
-		error = -EIO;	/* fs corruption? */
-		goto error_finish_iomap;
-	}
-
-	if (vmf->cow_page) {
-		sector_t sector = dax_iomap_sector(&iomap, pos);
-
-		switch (iomap.type) {
-		case IOMAP_HOLE:
-		case IOMAP_UNWRITTEN:
-			clear_user_highpage(vmf->cow_page, vaddr);
-			break;
-		case IOMAP_MAPPED:
-			error = copy_cow_page_dax(iomap.bdev, iomap.dax_dev,
-						  sector, vmf->cow_page, vaddr);
-			break;
-		default:
-			WARN_ON_ONCE(1);
-			error = -EIO;
-			break;
+	while ((error = iomap_iter(&iter, ops)) > 0) {
+		if (WARN_ON_ONCE(iomap_length(&iter) < PAGE_SIZE)) {
+			iter.processed = -EIO;	/* fs corruption? */
+			continue;
 		}
 
-		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) {
+		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(vma->vm_mm, PGMAJFAULT);
-			major = VM_FAULT_MAJOR;
+			count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
+			ret |= VM_FAULT_MAJOR;
 		}
-		error = dax_iomap_pfn(&iomap, pos, PAGE_SIZE, &pfn);
-		if (error < 0)
-			goto error_finish_iomap;
-
-		entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
-						 0, write && !sync);
 
-		/*
-		 * If we are doing synchronous page fault and inode needs fsync,
-		 * we can insert PTE into page tables only after that happens.
-		 * Skip insertion for now and return the pfn so that caller can
-		 * insert it after fsync is done.
-		 */
-		if (sync) {
-			if (WARN_ON_ONCE(!pfnp)) {
-				error = -EIO;
-				goto error_finish_iomap;
-			}
-			*pfnp = pfn;
-			ret = VM_FAULT_NEEDDSYNC | major;
-			goto finish_iomap;
-		}
-		trace_dax_insert_mapping(inode, vmf, entry);
-		if (write)
-			ret = vmf_insert_mixed_mkwrite(vma, vaddr, pfn);
-		else
-			ret = vmf_insert_mixed(vma, vaddr, pfn);
-
-		goto finish_iomap;
-	case IOMAP_UNWRITTEN:
-	case IOMAP_HOLE:
-		if (!write) {
-			ret = dax_load_hole(&xas, mapping, &entry, vmf);
-			goto finish_iomap;
-		}
-		fallthrough;
-	default:
-		WARN_ON_ONCE(1);
-		error = -EIO;
-		break;
+		if (!(ret & VM_FAULT_ERROR))
+			iter.processed = PAGE_SIZE;
 	}
 
- error_finish_iomap:
-	ret = dax_fault_return(error);
- finish_iomap:
-	if (ops->iomap_end) {
-		int copied = PAGE_SIZE;
+	if (iomap_errp)
+		*iomap_errp = error;
+	if (!ret && error)
+		ret = dax_fault_return(error);
 
-		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:
+unlock_entry:
 	dax_unlock_entry(&xas, entry);
- out:
-	trace_dax_pte_fault_done(inode, vmf, ret);
-	return ret | major;
+out:
+	trace_dax_pte_fault_done(iter.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,
-		struct iomap *iomap, void **entry)
+static bool dax_fault_check_fallback(struct vm_fault *vmf, struct xa_state *xas,
+		pgoff_t max_pgoff)
 {
-	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;
+	bool write = vmf->flags & FAULT_FLAG_WRITE;
 
-	pfn = page_to_pfn_t(zero_page);
-	*entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
-			DAX_PMD | DAX_ZERO_PAGE, false);
+	/*
+	 * 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;
 
-	if (arch_needs_pgtable_deposit()) {
-		pgtable = pte_alloc_one(vma->vm_mm);
-		if (!pgtable)
-			return VM_FAULT_OOM;
-	}
+	/* Fall back to PTEs if we're going to COW */
+	if (write && !(vmf->vma->vm_flags & VM_SHARED))
+		return true;
 
-	ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
-	if (!pmd_none(*(vmf->pmd))) {
-		spin_unlock(ptl);
-		goto fallback;
-	}
+	/* 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 (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;
+	/* If the PMD would extend beyond the file size */
+	if ((xas->xa_index | PG_PMD_COLOUR) >= max_pgoff)
+		return true;
 
-fallback:
-	if (pgtable)
-		pte_free(vma->vm_mm, pgtable);
-	trace_dax_pmd_load_hole_fallback(inode, vmf, zero_page, *entry);
-	return VM_FAULT_FALLBACK;
+	return false;
 }
 
 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;
+	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
 	XA_STATE_ORDER(xas, &mapping->i_pages, vmf->pgoff, PMD_ORDER);
-	unsigned long pmd_addr = vmf->address & PMD_MASK;
-	bool write = vmf->flags & FAULT_FLAG_WRITE;
-	bool sync;
-	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 = { .type = IOMAP_HOLE };
-	struct iomap srcmap = { .type = IOMAP_HOLE };
+	struct iomap_iter iter = {
+		.inode		= mapping->host,
+		.len		= PMD_SIZE,
+		.flags		= IOMAP_FAULT,
+	};
+	vm_fault_t ret = VM_FAULT_FALLBACK;
 	pgoff_t max_pgoff;
 	void *entry;
-	loff_t pos;
 	int error;
-	pfn_t pfn;
+
+	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(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 page cache.
-	 */
-	if ((vmf->pgoff & PG_PMD_COLOUR) !=
-	    ((vmf->address >> PAGE_SHIFT) & PG_PMD_COLOUR))
-		goto fallback;
+	max_pgoff = DIV_ROUND_UP(i_size_read(iter.inode), PAGE_SIZE);
 
-	/* 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;
+	trace_dax_pmd_fault(iter.inode, vmf, max_pgoff, 0);
 
 	if (xas.xa_index >= max_pgoff) {
-		result = VM_FAULT_SIGBUS;
+		ret = VM_FAULT_SIGBUS;
 		goto out;
 	}
 
-	/* If the PMD would extend beyond the file size */
-	if ((xas.xa_index | PG_PMD_COLOUR) >= max_pgoff)
+	if (dax_fault_check_fallback(vmf, &xas, max_pgoff))
 		goto fallback;
 
 	/*
@@ -1544,7 +1574,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	 */
 	entry = grab_mapping_entry(&xas, mapping, PMD_ORDER);
 	if (xa_is_internal(entry)) {
-		result = xa_to_internal(entry);
+		ret = xa_to_internal(entry);
 		goto fallback;
 	}
 
@@ -1556,88 +1586,30 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	 */
 	if (!pmd_none(*vmf->pmd) && !pmd_trans_huge(*vmf->pmd) &&
 			!pmd_devmap(*vmf->pmd)) {
-		result = 0;
+		ret = 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)xas.xa_index << PAGE_SHIFT;
-	error = ops->iomap_begin(inode, pos, PMD_SIZE, iomap_flags, &iomap,
-			&srcmap);
-	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_entry(&xas, mapping, vmf, entry, pfn,
-						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;
-		}
+	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 */
 
-		trace_dax_pmd_insert_mapping(inode, vmf, PMD_SIZE, pfn, entry);
-		result = vmf_insert_pfn_pmd(vmf, pfn, write);
-		break;
-	case IOMAP_UNWRITTEN:
-	case IOMAP_HOLE:
-		if (WARN_ON_ONCE(write))
-			break;
-		result = dax_pmd_load_hole(&xas, vmf, &iomap, &entry);
-		break;
-	default:
-		WARN_ON_ONCE(1);
-		break;
+		ret = dax_fault_iter(vmf, &iter, pfnp, &xas, &entry, true);
+		if (ret != VM_FAULT_FALLBACK)
+			iter.processed = PMD_SIZE;
 	}
 
- 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:
+unlock_entry:
 	dax_unlock_entry(&xas, entry);
- fallback:
-	if (result == VM_FAULT_FALLBACK) {
-		split_huge_pmd(vma, vmf->pmd, vmf->address);
+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(inode, vmf, max_pgoff, result);
-	return result;
+	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,