rmap: resurrect page_address_in_vma anon_vma check

With root anon-vma it's trivial to keep doing the usual check as in
old-anon-vma code.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/rmap.c

@@ -364,9 +364,10 @@ vma_address(struct page *page, struct vm_area_struct *vma)
  */
 unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
 {
-	if (PageAnon(page))
-		;
-	else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
+	if (PageAnon(page)) {
+		if (vma->anon_vma->root != page_anon_vma(page)->root)
+			return -EFAULT;
+	} else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
 		if (!vma->vm_file ||
 		    vma->vm_file->f_mapping != page->mapping)
 			return -EFAULT;