[PATCH v2 2/2] secretmem/gup: don't check if page is secretmem without reference

Mike Rapoport
2021-04-20T13:17:06Z

The check in gup_pte_range() whether a page belongs to a secretmem mapping
is performed before grabbing the page reference.

To avoid potential race move the check after try_grab_compound_head().

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
mm/gup.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index c3a17b189064..4b58c016e949 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2080,13 +2080,13 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = pte_page(pte);

- if (page_is_secretmem(page))
- goto pte_unmap;
-
head = try_grab_compound_head(page, 1, flags);
if (!head)
goto pte_unmap;

+ if (page_is_secretmem(page))
+ goto pte_unmap;
+
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
put_compound_head(head, 1, flags);
goto pte_unmap;