Messages in this thread | | | Date | Fri, 10 Jun 2022 17:47:12 +0100 | From | Catalin Marinas <> | Subject | Re: [PATCH] arm64: errata: add detection for AMEVCNTR01 incrementing incorrectly |
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On Tue, Jun 07, 2022 at 01:53:40PM +0100, Ionela Voinescu wrote: > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h > index 14a8f3d93add..80e0c700cecf 100644 > --- a/arch/arm64/include/asm/cpufeature.h > +++ b/arch/arm64/include/asm/cpufeature.h > @@ -881,11 +881,16 @@ static inline bool cpu_has_pan(void) > #ifdef CONFIG_ARM64_AMU_EXTN > /* Check whether the cpu supports the Activity Monitors Unit (AMU) */ > extern bool cpu_has_amu_feat(int cpu); > +extern bool cpu_has_broken_amu_constcnt(void); > #else > static inline bool cpu_has_amu_feat(int cpu) > { > return false; > } > +static inline bool cpu_has_broken_amu_constcnt(void) > +{ > + return false; > +} > #endif > > /* Get a cpu that supports the Activity Monitors Unit (AMU) */ > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index 42ea2bd856c6..b9e4b2bd2c63 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1791,6 +1791,19 @@ int get_cpu_with_amu_feat(void) > return cpumask_any(&amu_cpus); > } > > +bool cpu_has_broken_amu_constcnt(void) > +{ > + /* List of CPUs which have broken AMEVCNTR01 (constant counter) */ > + static const struct midr_range cpus[] = { > +#ifdef CONFIG_ARM64_ERRATUM_2457168 > + MIDR_RANGE(MIDR_CORTEX_A510, 0, 0, 1, 1), > +#endif > + {}, > + }; > + > + return is_midr_in_range(read_cpuid_id(), cpus); > +}
I'd rather not have this in cpufeature.c as it's not really a feature. We have some precedent with checking errata in cpufeature.c but IIRC we did that only to check whether to enable a feature or not in that file (DBM).
> + > static void cpu_amu_enable(struct arm64_cpu_capabilities const *cap) > { > if (has_cpuid_feature(cap, SCOPE_LOCAL_CPU)) { > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index 9ab78ad826e2..d4b0b0a40515 100644 > --- a/arch/arm64/kernel/topology.c > +++ b/arch/arm64/kernel/topology.c > @@ -127,7 +127,8 @@ int __init parse_acpi_topology(void) > > #ifdef CONFIG_ARM64_AMU_EXTN > #define read_corecnt() read_sysreg_s(SYS_AMEVCNTR0_CORE_EL0) > -#define read_constcnt() read_sysreg_s(SYS_AMEVCNTR0_CONST_EL0) > +#define read_constcnt() (cpu_has_broken_amu_constcnt() ? 0UL : \ > + read_sysreg_s(SYS_AMEVCNTR0_CONST_EL0))
How often is this called? You end up reading the cpuid, comparing the range on each call. I guess you can't use a cpucap in the arm64_errata[] array as you want a check per-CPU? Does it matter if we return 0UL on for all CPUs if one is affected?
-- Catalin
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