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Message-ID: <07cb1a4b-d4b1-3492-9126-c2ee860e784f@arm.com>
Date: Fri, 1 Oct 2021 10:08:16 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>,
linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org, maz@...nel.org,
catalin.marinas@....com, mark.rutland@....com, james.morse@....com,
leo.yan@...aro.org, mike.leach@...aro.org,
mathieu.poirier@...aro.org, will@...nel.org, lcherian@...vell.com,
coresight@...ts.linaro.org
Subject: Re: [PATCH v2 11/17] arm64: errata: Add workaround for TSB flush
failures
On 9/22/21 5:33 PM, Suzuki K Poulose wrote:
> 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@...nel.org>
>>> Cc: Catalin Marinas <catalin.marinas@....com>
>>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
>>> Cc: Mike Leach <mike.leach@...aro.org>
>>> Cc: Mark Rutland <mark.rutland@....com>
>>> Cc: Anshuman Khandual <anshuman.khandual@....com>
>>> Cc: Marc Zyngier <maz@...nel.org>
>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....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.
Okay, understood.
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