Messages in this thread Patch in this message | | | Date | Wed, 21 Mar 2018 15:31:19 +0000 | From | Dave Martin <> | Subject | Re: [PATCH v4 22/22] arm64: Add work around for Arm Cortex-A55 Erratum 1024718 |
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On Tue, Mar 13, 2018 at 11:51:20AM +0000, Suzuki K Poulose wrote: > Some variants of the Arm Cortex-55 cores (r0p0, r0p1, r1p0) suffer > from an erratum 1024718, which causes incorrect updates when DBM/AP > bits in a page table entry is modified without a break-before-make > sequence. The work around is to skip enabling the hardware DBM feature > on the affected cores. The hardware Access Flag management features > is not affected. There are some other cores suffering from this > errata, which could be added to the midr_list to trigger the work > around. > > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: ckadabi@codeaurora.org > Cc: Dave Martin <dave.martin@arm.com> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
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> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index 4e73c610a409..0fc097e2b72e 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -963,9 +963,23 @@ static inline void __cpu_enable_hw_dbm(void) > isb(); > } > > +static bool cpu_has_broken_dbm(void) > +{ > + /* List of CPUs which have broken DBM support. */ > + static const struct midr_range cpus[] = { > +#ifdef CONFIG_ARM64_ERRATUM_1024718 > + MIDR_RANGE(MIDR_CORTEX_A55, 0, 0, 1, 0), // A55 r0p0 -r1p0 > +#endif > + {}, > + }; > + > + return is_midr_in_range_list(read_cpuid_id(), cpus); > +} > + > static bool cpu_can_use_dbm(const struct arm64_cpu_capabilities *cap) > { > - return has_cpuid_feature(cap, SCOPE_LOCAL_CPU); > + return has_cpuid_feature(cap, SCOPE_LOCAL_CPU) && > + !cpu_has_broken_dbm();
This refactoring seems sensbile to me. The mapping between erratum IDs and features that don't work is never guaranteed to be 1:1, so it makes sense for the check function to have a generic name and to paste in the relevant erratum ID ranges depending on the kernel config.
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Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Cheers ---Dave
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