Messages in this thread | | | Subject | Re: [PATCH v2 11/17] arm64: errata: Add workaround for TSB flush failures | From | Suzuki K Poulose <> | Date | Wed, 22 Sep 2021 13:03:41 +0100 |
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Hi Anshuman
On 22/09/2021 08:39, Anshuman Khandual wrote: > > > On 9/21/21 7:11 PM, Suzuki K Poulose wrote: >> Arm Neoverse-N2 (#2067961) and Cortex-A710 (#2054223) suffers >> from errata, where a TSB (trace synchronization barrier) >> fails to flush the trace data completely, when executed from >> a trace prohibited region. In Linux we always execute it >> after we have moved the PE to trace prohibited region. So, >> we can apply the workaround everytime a TSB is executed. > > s/everytime/every time
Ack
> >> >> The work around is to issue two TSB consecutively. >> >> NOTE: This errata is defined as LOCAL_CPU_ERRATUM, implying >> that a late CPU could be blocked from booting if it is the >> first CPU that requires the workaround. This is because we >> do not allow setting a cpu_hwcaps after the SMP boot. The >> other alternative is to use "this_cpu_has_cap()" instead >> of the faster system wide check, which may be a bit of an >> overhead, given we may have to do this in nvhe KVM host >> before a guest entry. >> >> Cc: Will Deacon <will@kernel.org> >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: Mathieu Poirier <mathieu.poirier@linaro.org> >> Cc: Mike Leach <mike.leach@linaro.org> >> Cc: Mark Rutland <mark.rutland@arm.com> >> Cc: Anshuman Khandual <anshuman.khandual@arm.com> >> Cc: Marc Zyngier <maz@kernel.org> >> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >> ---
...
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >> index eac4030322df..0764774e12bb 100644 >> --- a/arch/arm64/Kconfig >> +++ b/arch/arm64/Kconfig >> @@ -705,6 +705,37 @@ config ARM64_ERRATUM_2139208 >> >> If unsure, say Y. >> >> +config ARM64_WORKAROUND_TSB_FLUSH_FAILURE >> + bool >> + >> +config ARM64_ERRATUM_2054223 >> + bool "Cortex-A710: 2054223: workaround TSB instruction failing to flush trace" >> + default y >> + help >> + Enable workaround for ARM Cortex-A710 erratum 2054223 >> + >> + Affected cores may fail to flush the trace data on a TSB instruction, when >> + the PE is in trace prohibited state. This will cause losing a few bytes >> + of the trace cached. >> + >> + Workaround is to issue two TSB consecutively on affected cores. >> + >> + If unsure, say Y. >> + >> +config ARM64_ERRATUM_2067961 >> + bool "Neoverse-N2: 2067961: workaround TSB instruction failing to flush trace" >> + default y >> + help >> + Enable workaround for ARM Neoverse-N2 erratum 2067961 >> + >> + Affected cores may fail to flush the trace data on a TSB instruction, when >> + the PE is in trace prohibited state. This will cause losing a few bytes >> + of the trace cached. >> + >> + Workaround is to issue two TSB consecutively on affected cores. > > Like I had mentioned in the previous patch, these descriptions here could > be just factored out inside ARM64_WORKAROUND_TSB_FLUSH_FAILURE instead.
Please see my response there.
> >> + >> + If unsure, say Y. >> + >> config CAVIUM_ERRATUM_22375 >> bool "Cavium erratum 22375, 24313" >> default y >> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h >> index 451e11e5fd23..1c5a00598458 100644 >> --- a/arch/arm64/include/asm/barrier.h >> +++ b/arch/arm64/include/asm/barrier.h >> @@ -23,7 +23,7 @@ >> #define dsb(opt) asm volatile("dsb " #opt : : : "memory") >> >> #define psb_csync() asm volatile("hint #17" : : : "memory") >> -#define tsb_csync() asm volatile("hint #18" : : : "memory") >> +#define __tsb_csync() asm volatile("hint #18" : : : "memory") >> #define csdb() asm volatile("hint #20" : : : "memory") >> >> #ifdef CONFIG_ARM64_PSEUDO_NMI >> @@ -46,6 +46,20 @@ >> #define dma_rmb() dmb(oshld) >> #define dma_wmb() dmb(oshst) >> >> + >> +#define tsb_csync() \ >> + do { \ >> + /* \ >> + * CPUs affected by Arm Erratum 2054223 or 2067961 needs \ >> + * another TSB to ensure the trace is flushed. The barriers \ >> + * don't have to be strictly back to back, as long as the \ >> + * CPU is in trace prohibited state. \ >> + */ \ >> + if (cpus_have_final_cap(ARM64_WORKAROUND_TSB_FLUSH_FAILURE)) \ >> + __tsb_csync(); \ >> + __tsb_csync(); \ >> + } while (0) >> + >> /* >> * Generate a mask for array_index__nospec() that is ~0UL when 0 <= idx < sz >> * and 0 otherwise. >> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c >> index ccd757373f36..bdbeac75ead6 100644 >> --- a/arch/arm64/kernel/cpu_errata.c >> +++ b/arch/arm64/kernel/cpu_errata.c >> @@ -352,6 +352,18 @@ static const struct midr_range trbe_overwrite_fill_mode_cpus[] = { >> }; >> #endif /* CONFIG_ARM64_WORKAROUND_TRBE_OVERWRITE_FILL_MODE */ >> >> +#ifdef CONFIG_ARM64_WORKAROUND_TSB_FLUSH_FAILURE >> +static const struct midr_range tsb_flush_fail_cpus[] = { >> +#ifdef CONFIG_ARM64_ERRATUM_2067961 >> + MIDR_ALL_VERSIONS(MIDR_NEOVERSE_N2), >> +#endif >> +#ifdef CONFIG_ARM64_ERRATUM_2054223 >> + MIDR_ALL_VERSIONS(MIDR_CORTEX_A710), >> +#endif >> + {}, >> +}; >> +#endif /* CONFIG_ARM64_WORKAROUND_TSB_FLUSH_FAILURE */ >> + >> const struct arm64_cpu_capabilities arm64_errata[] = { >> #ifdef CONFIG_ARM64_WORKAROUND_CLEAN_CACHE >> { >> @@ -558,6 +570,13 @@ const struct arm64_cpu_capabilities arm64_errata[] = { >> .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE, >> CAP_MIDR_RANGE_LIST(trbe_overwrite_fill_mode_cpus), >> }, >> +#endif >> +#ifdef CONFIG_ARM64_WORKAROUND_TSB_FLUSH_FAILRE >> + { >> + .desc = "ARM erratum 2067961 or 2054223", >> + .capability = ARM64_WORKAROUND_TSB_FLUSH_FAILURE, >> + ERRATA_MIDR_RANGE_LIST(tsb_flush_fail_cpus), >> + }, >> #endif >> { >> } >> diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps >> index 1ccb92165bd8..2102e15af43d 100644 >> --- a/arch/arm64/tools/cpucaps >> +++ b/arch/arm64/tools/cpucaps >> @@ -54,6 +54,7 @@ WORKAROUND_1463225 >> WORKAROUND_1508412 >> WORKAROUND_1542419 >> WORKAROUND_TRBE_OVERWRITE_FILL_MODE >> +WORKAROUND_TSB_FLUSH_FAILURE >> WORKAROUND_CAVIUM_23154 >> WORKAROUND_CAVIUM_27456 >> WORKAROUND_CAVIUM_30115 >> > > This adds all the required bits of these erratas in a single patch, > where as the previous work around had split all the required pieces > into multiple patches. Could we instead follow the same standard in > both the places ?
We could do this for this particular erratum as the work around is within the arm64 kernel code, unlike the other ones - where the TRBE driver needs a change.
So, there is a kind of dependency for the other two, which we don't in this particular case.
i.e, TRBE driver needs a cpucap number to implement the work around -> The arm64 kernel must define one, which we cant advertise yet until we have a TRBE work around.
Thus, they follow a 3 step model.
- Define CPUCAP erratum - TRBE driver work around - Finally advertise to the user.
I don't think this one needs that.
Suzuki
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