Commit 9025cebf authored by Joey Gouly's avatar Joey Gouly Committed by Catalin Marinas
Browse files

arm64: vdso: use SYS_CNTVCTSS_EL0 for gettimeofday 



If FEAT_ECV is implemented, the self-synchronized counter CNTVCTSS_EL0 can
be used, removing the need for an ISB.

Signed-off-by: default avatarJoey Gouly <joey.gouly@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Andre Przywara <andre.przywara@arm.com>
Acked-by: default avatarMark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20220830104833.34636-4-joey.gouly@arm.com


Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 4e3bca8f

arch/arm64/include/asm/vdso/gettimeofday.h

+15 −4
Original line number Diff line number Diff line
@@ -7,8 +7,10 @@ 


#ifndef __ASSEMBLY__



#include <asm/alternative.h>

#include <asm/barrier.h>

#include <asm/unistd.h>

#include <asm/sysreg.h>



#define VDSO_HAS_CLOCK_GETRES		1
@@ -78,11 +80,20 @@ 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\n"

		    "mrs %0, cntvct_el0",

		    "nop\n"

		    __mrs_s("%0", SYS_CNTVCTSS_EL0),

		    ARM64_HAS_ECV)

	: "=r" (res)

	:

	: "memory");



	arch_counter_enforce_ordering(res);



	return res;