linux-kernel - [PATCH V2 3/7] mm: Use ptep_get() for accessing PTE entries

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Message-Id: <20240917073117.1531207-4-anshuman.khandual@arm.com>
Date: Tue, 17 Sep 2024 13:01:13 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: linux-mm@...ck.org
Cc: Anshuman Khandual <anshuman.khandual@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>,
	"Mike Rapoport (IBM)" <rppt@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	x86@...nel.org,
	linux-m68k@...ts.linux-m68k.org,
	linux-fsdevel@...r.kernel.org,
	kasan-dev@...glegroups.com,
	linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org
Subject: [PATCH V2 3/7] mm: Use ptep_get() for accessing PTE entries

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.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>
Cc: Ryan Roberts <ryan.roberts@....com>
Cc: "Mike Rapoport (IBM)" <rppt@...nel.org>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
 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); \
 })
 
-- 
2.25.1