arm64: mm: Use READ_ONCE/WRITE_ONCE when accessing page tables

In many cases, page tables can be accessed concurrently by either another
CPU (due to things like fast gup) or by the hardware page table walker
itself, which may set access/dirty bits. In such cases, it is important
to use READ_ONCE/WRITE_ONCE when accessing page table entries so that
entries cannot be torn, merged or subject to apparent loss of coherence
due to compiler transformations.

Whilst there are some scenarios where this cannot happen (e.g. pinned
kernel mappings for the linear region), the overhead of using READ_ONCE
/WRITE_ONCE everywhere is minimal and makes the code an awful lot easier
to reason about. This patch consistently uses these macros in the arch
code, as well as explicitly namespacing pointers to page table entries
from the entries themselves by using adopting a 'p' suffix for the former
(as is sometimes used elsewhere in the kernel source).

Tested-by: Yury Norov <ynorov@caviumnetworks.com>
Tested-by: Richard Ruigrok <rruigrok@codeaurora.org>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 13 insertions, 13 deletions

diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 9679067a1574..7faed6e48b46 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -185,42 +185,42 @@ static inline pmd_t kvm_s2pmd_mkexec(pmd_t pmd)
 	return pmd;
 }
 
-static inline void kvm_set_s2pte_readonly(pte_t *pte)
+static inline void kvm_set_s2pte_readonly(pte_t *ptep)
 {
 	pteval_t old_pteval, pteval;
 
-	pteval = READ_ONCE(pte_val(*pte));
+	pteval = READ_ONCE(pte_val(*ptep));
 	do {
 		old_pteval = pteval;
 		pteval &= ~PTE_S2_RDWR;
 		pteval |= PTE_S2_RDONLY;
-		pteval = cmpxchg_relaxed(&pte_val(*pte), old_pteval, pteval);
+		pteval = cmpxchg_relaxed(&pte_val(*ptep), old_pteval, pteval);
 	} while (pteval != old_pteval);
 }
 
-static inline bool kvm_s2pte_readonly(pte_t *pte)
+static inline bool kvm_s2pte_readonly(pte_t *ptep)
 {
-	return (pte_val(*pte) & PTE_S2_RDWR) == PTE_S2_RDONLY;
+	return (READ_ONCE(pte_val(*ptep)) & PTE_S2_RDWR) == PTE_S2_RDONLY;
 }
 
-static inline bool kvm_s2pte_exec(pte_t *pte)
+static inline bool kvm_s2pte_exec(pte_t *ptep)
 {
-	return !(pte_val(*pte) & PTE_S2_XN);
+	return !(READ_ONCE(pte_val(*ptep)) & PTE_S2_XN);
 }
 
-static inline void kvm_set_s2pmd_readonly(pmd_t *pmd)
+static inline void kvm_set_s2pmd_readonly(pmd_t *pmdp)
 {
-	kvm_set_s2pte_readonly((pte_t *)pmd);
+	kvm_set_s2pte_readonly((pte_t *)pmdp);
 }
 
-static inline bool kvm_s2pmd_readonly(pmd_t *pmd)
+static inline bool kvm_s2pmd_readonly(pmd_t *pmdp)
 {
-	return kvm_s2pte_readonly((pte_t *)pmd);
+	return kvm_s2pte_readonly((pte_t *)pmdp);
 }
 
-static inline bool kvm_s2pmd_exec(pmd_t *pmd)
+static inline bool kvm_s2pmd_exec(pmd_t *pmdp)
 {
-	return !(pmd_val(*pmd) & PMD_S2_XN);
+	return !(READ_ONCE(pmd_val(*pmdp)) & PMD_S2_XN);
 }
 
 static inline bool kvm_page_empty(void *ptr)