[PATCH RFC 03/13] mm/gup: Check p4d presence before going on

peterx
2024-03-06T10:42:25Z

Currently there should have no p4d swap entries so it may not matter much,
however this may help us to rule out swap entries in pXd_huge() API, which
will include p4d_huge(). The p4d_present() checks make it 100% clear that
we won't rely on p4d_huge() for swap entries.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
mm/gup.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 69a777f4fc5c..f87a7d90f2ae 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -776,7 +776,7 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma,

p4dp = p4d_offset(pgdp, address);
p4d = READ_ONCE(*p4dp);
- if (p4d_none(p4d))
+ if (p4d_none(p4d) || !p4d_present(p4d))
return no_page_table(vma, flags);
BUILD_BUG_ON(p4d_huge(p4d));
if (unlikely(p4d_bad(p4d)))
@@ -3069,7 +3069,7 @@ static int gup_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr, unsigned lo
p4d_t p4d = READ_ONCE(*p4dp);

next = p4d_addr_end(addr, end);
- if (p4d_none(p4d))
+ if (p4d_none(p4d) || !p4d_present(p4d))
return 0;
BUILD_BUG_ON(p4d_huge(p4d));
if (unlikely(is_hugepd(__hugepd(p4d_val(p4d))))) {
--
2.44.0