dax: update PMD fault handler with PMEM API

As part of the v4.3 merge window the DAX code was updated by Matthew and
Kirill to handle PMD pages.  Also as part of the v4.3 merge window we
updated the DAX code to do proper PMEM flushing (commit 2765cfbb342c:
"dax: update I/O path to do proper PMEM flushing").

The additional code added by the DAX PMD patches also needs to be
updated to properly use the PMEM API.  This ensures that after a PMD
fault is handled the zeros written to the newly allocated pages are
durable on the DIMMs.

linux/dax.h is included to get rid of a bunch of sparse warnings.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Matthew Wilcox <willy@linux.intel.com>,
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Kirill Shutemov <kirill@shutemov.name>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/dax.c b/fs/dax.c
index e43389c..93bf2f9 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -17,6 +17,7 @@
 #include <linux/atomic.h>
 #include <linux/blkdev.h>
 #include <linux/buffer_head.h>
+#include <linux/dax.h>
 #include <linux/fs.h>
 #include <linux/genhd.h>
 #include <linux/highmem.h>
@@ -527,7 +528,7 @@
 	unsigned long pmd_addr = address & PMD_MASK;
 	bool write = flags & FAULT_FLAG_WRITE;
 	long length;
-	void *kaddr;
+	void __pmem *kaddr;
 	pgoff_t size, pgoff;
 	sector_t block, sector;
 	unsigned long pfn;
@@ -570,7 +571,8 @@
 	if (buffer_unwritten(&bh) || buffer_new(&bh)) {
 		int i;
 		for (i = 0; i < PTRS_PER_PMD; i++)
-			clear_page(kaddr + i * PAGE_SIZE);
+			clear_pmem(kaddr + i * PAGE_SIZE, PAGE_SIZE);
+		wmb_pmem();
 		mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
 		result |= VM_FAULT_MAJOR;