[PATCH v1 3/3] arm64: vdso: use SYS_CNTVCTSS_EL0 for gettimeofday
Mark Rutland
mark.rutland at arm.com
Thu Aug 25 06:24:22 PDT 2022
On Thu, Aug 25, 2022 at 11:20:25AM +0100, Joey Gouly wrote:
> If FEAT_ECV is implemented, the self-synchronized counter CNTVCTSS_EL0 can
> be used, removing the need for an ISB.
>
> Signed-off-by: Joey Gouly <joey.gouly at arm.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will at kernel.org>
> Cc: Vincenzo Frascino <vincenzo.frascino at arm.com>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Andre Przywara <andre.przywara at arm.com>
> ---
> arch/arm64/include/asm/vdso/gettimeofday.h | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/include/asm/vdso/gettimeofday.h b/arch/arm64/include/asm/vdso/gettimeofday.h
> index 4f7a629df81f..d8aff747019c 100644
> --- a/arch/arm64/include/asm/vdso/gettimeofday.h
> +++ b/arch/arm64/include/asm/vdso/gettimeofday.h
> @@ -9,6 +9,8 @@
>
> #include <asm/barrier.h>
> #include <asm/unistd.h>
> +#include <asm/sysreg.h>
> +#include <asm/alternative.h>
Nit: please sort this alphabetically.
>
> #define VDSO_HAS_CLOCK_GETRES 1
>
> @@ -78,11 +80,15 @@ static __always_inline u64 __arch_get_hw_counter(s32 clock_mode,
> return 0;
>
> /*
> - * This isb() is required to prevent that the counter value
> + * If FEAT_ECV is available, use the self-synchronizing counter.
> + * Otherwise the isb is required to prevent that the counter value
> * is speculated.
> - */
> - isb();
> - asm volatile("mrs %0, cntvct_el0" : "=r" (res) :: "memory");
> + */
> + asm volatile(ALTERNATIVE("isb\nmrs %0, cntvct_el0",
> + "nop\n" __mrs_s("%0", SYS_CNTVCTSS_EL0),
> + ARM64_HAS_ECV)
> + : "=r" (res) :: "memory");
> +
For legibility (and ease of future modification), could we please format this
with the fields all aligned, e.g.
asm volatile(
ALTERNATIVE("isb\n"
"mrs %0, cntvct_el0",
"nop\n"
__mrs_s("%0", SYS_CNTVCTSS_EL0),
ARM64_HAS_ECV)
: "=r" (res)
:
: "memory");
Regardless:
Acked-by: Mark Rutland <mark.rutland at arm.com>
Thanks,
Mark.
> arch_counter_enforce_ordering(res);
>
> return res;
> --
> 2.17.1
>
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