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Date: Sun, 17 Oct 2021 13:42:23 +0100 From: Marc Zyngier <maz@...nel.org> To: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, Daniel Lezcano <daniel.lezcano@...aro.org>, Will Deacon <will@...nel.org> Cc: Mark Rutland <mark.rutland@....com>, Thomas Gleixner <tglx@...utronix.de>, Peter Shier <pshier@...gle.com>, Raghavendra Rao Ananta <rananta@...gle.com>, Ricardo Koller <ricarkol@...gle.com>, Oliver Upton <oupton@...gle.com>, Catalin Marinas <catalin.marinas@....com>, Linus Walleij <linus.walleij@...aro.org>, kernel-team@...roid.com Subject: [PATCH v4 15/17] arm64: Add CNT{P,V}CTSS_EL0 alternatives to cnt{p,v}ct_el0 CNTPCTSS_EL0 and CNTVCTSS_EL0 are alternatives to the usual CNTPCT_EL0 and CNTVCT_EL0 that do not require a previous ISB to be synchronised (SS stands for Self-Synchronising). Use the ARM64_HAS_ECV capability to control alternative sequences that switch to these low(er)-cost primitives. Note that the counter access in the VDSO is for now left alone until we decide whether we want to allow this. Signed-off-by: Marc Zyngier <maz@...nel.org> --- arch/arm64/include/asm/arch_timer.h | 32 +++++++++++++++++++++-------- arch/arm64/include/asm/sysreg.h | 3 +++ 2 files changed, 27 insertions(+), 8 deletions(-) diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h index 519ac1f7f859..af1fafbe7e1d 100644 --- a/arch/arm64/include/asm/arch_timer.h +++ b/arch/arm64/include/asm/arch_timer.h @@ -64,14 +64,26 @@ DECLARE_PER_CPU(const struct arch_timer_erratum_workaround *, static inline notrace u64 arch_timer_read_cntpct_el0(void) { - isb(); - return read_sysreg(cntpct_el0); + u64 cnt; + + asm volatile(ALTERNATIVE("isb\n mrs %0, cntpct_el0", + "nop\n" __mrs_s("%0", SYS_CNTPCTSS_EL0), + ARM64_HAS_ECV) + : "=r" (cnt)); + + return cnt; } static inline notrace u64 arch_timer_read_cntvct_el0(void) { - isb(); - return read_sysreg(cntvct_el0); + u64 cnt; + + asm volatile(ALTERNATIVE("isb\n mrs %0, cntvct_el0", + "nop\n" __mrs_s("%0", SYS_CNTVCTSS_EL0), + ARM64_HAS_ECV) + : "=r" (cnt)); + + return cnt; } #define arch_timer_reg_read_stable(reg) \ @@ -174,8 +186,10 @@ static __always_inline u64 __arch_counter_get_cntpct(void) { u64 cnt; - isb(); - cnt = read_sysreg(cntpct_el0); + asm volatile(ALTERNATIVE("isb\n mrs %0, cntpct_el0", + "nop\n" __mrs_s("%0", SYS_CNTPCTSS_EL0), + ARM64_HAS_ECV) + : "=r" (cnt)); arch_counter_enforce_ordering(cnt); return cnt; } @@ -193,8 +207,10 @@ static __always_inline u64 __arch_counter_get_cntvct(void) { u64 cnt; - isb(); - cnt = read_sysreg(cntvct_el0); + asm volatile(ALTERNATIVE("isb\n mrs %0, cntvct_el0", + "nop\n" __mrs_s("%0", SYS_CNTVCTSS_EL0), + ARM64_HAS_ECV) + : "=r" (cnt)); arch_counter_enforce_ordering(cnt); return cnt; } diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h index b268082d67ed..5ce70c034d37 100644 --- a/arch/arm64/include/asm/sysreg.h +++ b/arch/arm64/include/asm/sysreg.h @@ -507,6 +507,9 @@ #define SYS_CNTFRQ_EL0 sys_reg(3, 3, 14, 0, 0) +#define SYS_CNTPCTSS_EL0 sys_reg(3, 3, 14, 0, 5) +#define SYS_CNTVCTSS_EL0 sys_reg(3, 3, 14, 0, 6) + #define SYS_CNTP_TVAL_EL0 sys_reg(3, 3, 14, 2, 0) #define SYS_CNTP_CTL_EL0 sys_reg(3, 3, 14, 2, 1) #define SYS_CNTP_CVAL_EL0 sys_reg(3, 3, 14, 2, 2) -- 2.30.2
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