On arm64 without hardware Access Flag, copying from user will fail because
the pte is old and cannot be marked young. So we always end up with zeroed
page after fork() + CoW for pfn mappings. We don't always have a
hardware-managed Access Flag on arm64.
Hence implement arch_faults_on_old_pte on arm64 to indicate that it might
cause page fault when accessing old pte.
Signed-off-by: Jia He <justin.he@xxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
---
arch/arm64/include/asm/pgtable.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 7576df00eb50..e96fb82f62de 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -885,6 +885,20 @@ static inline void update_mmu_cache(struct vm_area_struct *vma,
#define phys_to_ttbr(addr) (addr)
#endif
+/*
+ * On arm64 without hardware Access Flag, copying from user will fail because
+ * the pte is old and cannot be marked young. So we always end up with zeroed
+ * page after fork() + CoW for pfn mappings. We don't always have a
+ * hardware-managed access flag on arm64.
+ */
+static inline bool arch_faults_on_old_pte(void)
+{
+ WARN_ON(preemptible());
+
+ return !cpu_has_hw_af();
+}
+#define arch_faults_on_old_pte arch_faults_on_old_pte
+
#endif /* !__ASSEMBLY__ */
#endif /* __ASM_PGTABLE_H */
--
2.17.1
