mm: fix status code which move_pages() returns for zero page

The manpage for move_pages(2) specifies that status code for zero page is
supposed to be -EFAULT.  Currently kernel return -ENOENT in this case.

follow_page() can do it for us, if we would ask for FOLL_DUMP.  The use of
FOLL_DUMP also means that the upper layer page tables pages are no longer
allocated.
Signed-off-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: NChristoph Lameter <cl@linux.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/migrate.c

@@ -1226,7 +1226,9 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
 		if (!vma || pp->addr < vma->vm_start || !vma_migratable(vma))
 			goto set_status;
 
-		page = follow_page(vma, pp->addr, FOLL_GET|FOLL_SPLIT);
+		/* FOLL_DUMP to ignore special (like zero) pages */
+		page = follow_page(vma, pp->addr,
+				FOLL_GET | FOLL_SPLIT | FOLL_DUMP);
 
 		err = PTR_ERR(page);
 		if (IS_ERR(page))
@@ -1236,10 +1238,6 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
 		if (!page)
 			goto set_status;
 
-		/* Use PageReserved to check for zero page */
-		if (PageReserved(page))
-			goto put_and_set;
-
 		pp->page = page;
 		err = page_to_nid(page);
 
@@ -1396,18 +1394,14 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
 		if (!vma || addr < vma->vm_start)
 			goto set_status;
 
-		page = follow_page(vma, addr, 0);
+		/* FOLL_DUMP to ignore special (like zero) pages */
+		page = follow_page(vma, addr, FOLL_DUMP);
 
 		err = PTR_ERR(page);
 		if (IS_ERR(page))
 			goto set_status;
 
-		err = -ENOENT;
-		/* Use PageReserved to check for zero page */
-		if (!page || PageReserved(page))
-			goto set_status;
-
-		err = page_to_nid(page);
+		err = page ? page_to_nid(page) : -ENOENT;
 set_status:
 		*status = err;