[PATCH v1 3/3] arm64: vdso: use SYS_CNTVCTSS_EL0 for gettimeofday
Joey Gouly
joey.gouly at arm.com
Thu Aug 25 03:20:25 PDT 2022
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>
#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");
+
arch_counter_enforce_ordering(res);
return res;
--
2.17.1
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