diff options
| author | Will Deacon <will@kernel.org> | 2021-03-18 17:07:37 +0000 |
|---|---|---|
| committer | Catalin Marinas <catalin.marinas@arm.com> | 2021-03-24 16:48:41 +0000 |
| commit | 77ec462536a13d4b428a1eead725c4818a49f0b1 (patch) | |
| tree | 85563cf866233aaa24c0ea0961da46c17362e724 | |
| parent | 7adbf10e29c2323f5eb6d6bdd13050c70900b993 (diff) | |
| download | linux-77ec462536a13d4b428a1eead725c4818a49f0b1.tar.bz2 | |
arm64: vdso: Avoid ISB after reading from cntvct_el0
We can avoid the expensive ISB instruction after reading the counter in
the vDSO gettime functions by creating a fake address hazard against a
dummy stack read, just like we do inside the kernel.
Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lore.kernel.org/r/20210318170738.7756-5-will@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
| -rw-r--r-- | arch/arm64/include/asm/arch_timer.h | 21 | ||||
| -rw-r--r-- | arch/arm64/include/asm/barrier.h | 19 | ||||
| -rw-r--r-- | arch/arm64/include/asm/vdso/gettimeofday.h | 6 |
3 files changed, 20 insertions, 26 deletions
diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h index 9f0ec21d6327..88d20f04c64a 100644 --- a/arch/arm64/include/asm/arch_timer.h +++ b/arch/arm64/include/asm/arch_timer.h @@ -165,25 +165,6 @@ static inline void arch_timer_set_cntkctl(u32 cntkctl) isb(); } -/* - * Ensure that reads of the counter are treated the same as memory reads - * for the purposes of ordering by subsequent memory barriers. - * - * This insanity brought to you by speculative system register reads, - * out-of-order memory accesses, sequence locks and Thomas Gleixner. - * - * http://lists.infradead.org/pipermail/linux-arm-kernel/2019-February/631195.html - */ -#define arch_counter_enforce_ordering(val) do { \ - u64 tmp, _val = (val); \ - \ - asm volatile( \ - " eor %0, %1, %1\n" \ - " add %0, sp, %0\n" \ - " ldr xzr, [%0]" \ - : "=r" (tmp) : "r" (_val)); \ -} while (0) - static __always_inline u64 __arch_counter_get_cntpct_stable(void) { u64 cnt; @@ -224,8 +205,6 @@ static __always_inline u64 __arch_counter_get_cntvct(void) return cnt; } -#undef arch_counter_enforce_ordering - static inline int arch_timer_arch_init(void) { return 0; diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h index c3009b0e5239..37d891af8ea5 100644 --- a/arch/arm64/include/asm/barrier.h +++ b/arch/arm64/include/asm/barrier.h @@ -70,6 +70,25 @@ static inline unsigned long array_index_mask_nospec(unsigned long idx, return mask; } +/* + * Ensure that reads of the counter are treated the same as memory reads + * for the purposes of ordering by subsequent memory barriers. + * + * This insanity brought to you by speculative system register reads, + * out-of-order memory accesses, sequence locks and Thomas Gleixner. + * + * http://lists.infradead.org/pipermail/linux-arm-kernel/2019-February/631195.html + */ +#define arch_counter_enforce_ordering(val) do { \ + u64 tmp, _val = (val); \ + \ + asm volatile( \ + " eor %0, %1, %1\n" \ + " add %0, sp, %0\n" \ + " ldr xzr, [%0]" \ + : "=r" (tmp) : "r" (_val)); \ +} while (0) + #define __smp_mb() dmb(ish) #define __smp_rmb() dmb(ishld) #define __smp_wmb() dmb(ishst) diff --git a/arch/arm64/include/asm/vdso/gettimeofday.h b/arch/arm64/include/asm/vdso/gettimeofday.h index 631ab1281633..4b4c0dac0e14 100644 --- a/arch/arm64/include/asm/vdso/gettimeofday.h +++ b/arch/arm64/include/asm/vdso/gettimeofday.h @@ -83,11 +83,7 @@ static __always_inline u64 __arch_get_hw_counter(s32 clock_mode, */ isb(); asm volatile("mrs %0, cntvct_el0" : "=r" (res) :: "memory"); - /* - * This isb() is required to prevent that the seq lock is - * speculated.# - */ - isb(); + arch_counter_enforce_ordering(res); return res; } |