mm: pagewalk: call pte_hole() for VM_PFNMAP during walk_page_range

walk_page_range silently skips vma having VM_PFNMAP set, which leads to undesirable behaviour at client end (who called walk_page_range). For example for pagemap_read, when no callbacks are called against VM_PFNMAP vma, pagemap_read may prepare pagemap data for next virtual address range at wrong index.

Signed-off-by Shiraz Hashim <[email protected]>

---
The fix is revised, based upon the suggestion here at
http://www.spinics.net/lists/linux-mm/msg83058.html

 mm/pagewalk.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

mm/pagewalk.c +4 -1

index ad83195..b264bda 100644
@@ -199,7 +199,10 @@ int walk_page_range(unsigned long addr, unsigned long end,
 			 */
 			if ((vma->vm_start <= addr) &&
 			    (vma->vm_flags & VM_PFNMAP)) {
-				next = vma->vm_end;
+				if (walk->pte_hole)
+					err = walk->pte_hole(addr, next, walk);
+				if (err)
+					break;
 				pgd = pgd_offset(walk->mm, next);
 				continue;
 			}

Signature · 10 lines

Shiraz Hashim

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walk_page_range silently skips vma having VM_PFNMAP set, which leads to undesirable behaviour at client end (who called walk_page_range). For example for pagemap_read, when no callbacks are called against VM_PFNMAP vma, pagemap_read may prepare pagemap data for next virtual address range at wrong index.