[PATCH 4/6] mm/gup: handle ZONE_DEVICE pages in folio_fast_pin_allowed()

Martin Oliveira
2024-06-05T19:30:17Z

folio_fast_pin_allowed() does not support ZONE_DEVICE pages because
currently it is impossible for that type of page to be used with
FOLL_LONGTERM. When this changes in a subsequent patch, this path will
attempt to read the mapping of a ZONE_DEVICE page which is not valid.

Instead, allow ZONE_DEVICE pages explicitly seeing they shouldn't pose
any problem with the fast path.

Co-developed-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Martin Oliveira <martin.oliveira@eideticom.com>
---
mm/gup.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index ca0f5cedce9b..00d0a77112f4 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2847,6 +2847,10 @@ static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags)
if (folio_test_hugetlb(folio))
return true;

+ /* It makes no sense to access the mapping of ZONE_DEVICE pages */
+ if (folio_is_zone_device(folio))
+ return true;
+
/*
* GUP-fast disables IRQs. When IRQS are disabled, RCU grace periods
* cannot proceed, which means no actions performed under RCU can
--
2.34.1