mm: Allow arches to provide ptep_get()

Since commit 9e343b467c70 ("READ_ONCE: Enforce atomicity for
{READ,WRITE}_ONCE() memory accesses") it is not possible anymore to
use READ_ONCE() to access complex page table entries like the one
defined for powerpc 8xx with 16k size pages.

Define a ptep_get() helper that architectures can override instead
of performing a READ_ONCE() on the page table entry pointer.

Fixes: 9e343b467c70 ("READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses")
Signed-off-by: Christophe Leroy <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/087fa12b6e920e32315136b998aa834f99242695.1592225558.git.christophe.leroy@csgroup.eu

diff --git a/include/asm-generic/hugetlb.h b/include/asm-generic/hugetlb.h
index 40f85decc2ee50caf0ff3549ecbcf956ba0b9240..8e1e6244a89da29ac01406e463e41ae202b45f9d 100644 (file)
--- a/include/asm-generic/hugetlb.h
+++ b/include/asm-generic/hugetlb.h
@@ -122,7 +122,7 @@ static inline int huge_ptep_set_access_flags(struct vm_area_struct *vma,
 #ifndef __HAVE_ARCH_HUGE_PTEP_GET
 static inline pte_t huge_ptep_get(pte_t *ptep)
 {
-       return READ_ONCE(*ptep);
+       return ptep_get(ptep);
 }
 #endif
 

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 32b6c52d41b95ab07b56fc3f9eb77a9e71cfada3..56c1e8eb7bb0a095a9c5060e417fba63734129b8 100644 (file)
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -249,6 +249,13 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
 }
 #endif
 
+#ifndef __HAVE_ARCH_PTEP_GET
+static inline pte_t ptep_get(pte_t *ptep)
+{
+       return READ_ONCE(*ptep);
+}
+#endif
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 #ifndef __HAVE_ARCH_PMDP_HUGE_GET_AND_CLEAR
 static inline pmd_t pmdp_huge_get_and_clear(struct mm_struct *mm,

diff --git a/mm/gup.c b/mm/gup.c
index 761df4944ef5afd012cfc023982f1da34b74d069..6f47697f8fb0b2320cd5df12f2e073ba1b0ee598 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2196,7 +2196,7 @@ static inline pte_t gup_get_pte(pte_t *ptep)
  */
 static inline pte_t gup_get_pte(pte_t *ptep)
 {
-       return READ_ONCE(*ptep);
+       return ptep_get(ptep);
 }
 #endif /* CONFIG_GUP_GET_PTE_LOW_HIGH */