From: Matthew Wilcox <redacted>

vm_insert_mixed() will fail if there is already a valid PTE at that
location.  The DAX code would rather replace the previous value with
the new PTE.

Signed-off-by: Matthew Wilcox <redacted>
---
 include/linux/mm.h |  8 ++++++--
 mm/memory.c        | 34 +++++++++++++++++++++-------------
 2 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e04f531..8d1194c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -1958,8 +1958,12 @@ int remap_pfn_range(struct vm_area_struct *, unsigned long addr,
 int vm_insert_page(struct vm_area_struct *, unsigned long addr, struct page *);
 int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
 			unsigned long pfn);
-int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
-			unsigned long pfn);
+int __vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
+			unsigned long pfn, bool replace);
+#define vm_insert_mixed(vma, addr, pfn)	\
+	__vm_insert_mixed(vma, addr, pfn, false)
+#define vm_replace_mixed(vma, addr, pfn)	\
+	__vm_insert_mixed(vma, addr, pfn, true)
 int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len);
 
 

diff --git a/mm/memory.c b/mm/memory.c
index 42bf429..cf06c97 100644
--- a/mm/memory.c
+++ b/mm/memory.c

@@ -1476,7 +1476,7 @@ pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
  * pages reserved for the old functions anyway.
  */
 static int insert_page(struct vm_area_struct *vma, unsigned long addr,
-			struct page *page, pgprot_t prot)
+			struct page *page, pgprot_t prot, bool replace)
 {
 	struct mm_struct *mm = vma->vm_mm;
 	int retval;

@@ -1492,8 +1492,12 @@ static int insert_page(struct vm_area_struct *vma, unsigned long addr,
 	if (!pte)
 		goto out;
 	retval = -EBUSY;
-	if (!pte_none(*pte))
-		goto out_unlock;
+	if (!pte_none(*pte)) {
+		if (!replace)
+			goto out_unlock;
+		VM_BUG_ON(!mutex_is_locked(&vma->vm_file->f_mapping->i_mmap_mutex));
+		zap_page_range_single(vma, addr, PAGE_SIZE, NULL);