1 files changed, 13 insertions, 1 deletions

diff --git a/mm/memory.c b/mm/memory.c
index d14b251a25a6..350e646032f5 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1697,8 +1697,19 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
         struct page *dirty_page = NULL;
 
         old_page = vm_normal_page(vma, address, orig_pte);
-        if (!old_page)
+        if (!old_page) {
+                /*
+                 * VM_MIXEDMAP !pfn_valid() case
+                 *
+                 * We should not cow pages in a shared writeable mapping.
+                 * Just mark the pages writable as we can't do any dirty
+                 * accounting on raw pfn maps.
+                 */
+                if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
+                                     (VM_WRITE|VM_SHARED))
+                        goto reuse;
                 goto gotten;
+        }
 
         /*
          * Take out anonymous pages first, anonymous shared vmas are
@@ -1751,6 +1762,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
         }
 
         if (reuse) {
+reuse:
                 flush_cache_page(vma, address, pte_pfn(orig_pte));
                 entry = pte_mkyoung(orig_pte);
                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);