On 17.09.24 09:31, Anshuman Khandual wrote:
Convert PTE accesses via ptep_get() helper that defaults as READ_ONCE() but
also provides the platform an opportunity to override when required. This
stores read page table entry value in a local variable which can be used in
multiple instances there after. This helps in avoiding multiple memory load
operations as well possible race conditions.
Please make it clearer in the subject+description that this really only
involves set_pte_safe().
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: "Mike Rapoport (IBM)" <rppt@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
---
include/linux/pgtable.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 2a6a3cccfc36..547eeae8c43f 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1060,7 +1060,8 @@ static inline int pgd_same(pgd_t pgd_a, pgd_t pgd_b)
*/
#define set_pte_safe(ptep, pte) \
({ \
- WARN_ON_ONCE(pte_present(*ptep) && !pte_same(*ptep, pte)); \
+ pte_t __old = ptep_get(ptep); \
+ WARN_ON_ONCE(pte_present(__old) && !pte_same(__old, pte)); \
set_pte(ptep, pte); \
})
I don't think this is necessary. PTE present cannot flip concurrently,
that's the whole reason of the "safe" part after all.
Can we just move these weird set_pte/pmd_safe() stuff to x86 init code
and be done with it? Then it's also clear *where* it is getting used and
for which reason.
--
Cheers,
David / dhildenb
