On Sat, Sep 21, 2019 at 09:50:53PM +0800, Jia He wrote:
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index e09760ece844..4a9939615e41 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -868,6 +868,18 @@ 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 fromuser will fail because
^^^^^^^^
from user
> + * 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
^^
We
> + * hardware-managed access flag on arm64.
> + */
> +static inline bool arch_faults_on_old_pte(void)
> +{
> + return !cpu_has_hw_af();
I saw an early incarnation of your patch having a
WARN_ON(preemptible()). I think we need this back just in case this
function will be used elsewhere in the future.
> +}
> +#define arch_faults_on_old_pte arch_faults_on_old_pte
Otherwise,
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
