1 files changed, 10 insertions, 2 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index e6ee12344b13..6446c6134b04 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1065,7 +1065,8 @@ munmap_back:
         vma->vm_start = addr;
         vma->vm_end = addr + len;
         vma->vm_flags = vm_flags;
-        vma->vm_page_prot = protection_map[vm_flags & 0x0f];
+        vma->vm_page_prot = protection_map[vm_flags &
+                                (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
         vma->vm_pgoff = pgoff;
 
         if (file) {
@@ -1089,6 +1090,12 @@ munmap_back:
                         goto free_vma;
         }
 
+        /* Don't make the VMA automatically writable if it's shared, but the
+         * backer wishes to know when pages are first written to */
+        if (vma->vm_ops && vma->vm_ops->page_mkwrite)
+                vma->vm_page_prot =
+                        protection_map[vm_flags & (VM_READ|VM_WRITE|VM_EXEC)];
+
         /* We set VM_ACCOUNT in a shared mapping's vm_flags, to inform
          * shmem_zero_setup (perhaps called through /dev/zero's ->mmap)
          * that memory reservation must be checked; but that reservation
@@ -1921,7 +1928,8 @@ unsigned long do_brk(unsigned long addr, unsigned long len)
         vma->vm_end = addr + len;
         vma->vm_pgoff = pgoff;
         vma->vm_flags = flags;
-        vma->vm_page_prot = protection_map[flags & 0x0f];
+        vma->vm_page_prot = protection_map[flags &
+                                (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
         vma_link(mm, vma, prev, rb_link, rb_parent);
 out:
         mm->total_vm += len >> PAGE_SHIFT;