linux-kernel - Re: [PATCH v3 02/10] perf: arm_spe: Support FEAT

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Message-ID: <7b080e97-375d-4521-b167-d0c4256dc464@linaro.org>
Date: Thu, 12 Jun 2025 09:42:39 +0100
From: James Clark <james.clark@...aro.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-perf-users@...r.kernel.org, linux-doc@...r.kernel.org,
 kvmarm@...ts.linux.dev, Catalin Marinas <catalin.marinas@....com>,
 Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>,
 Oliver Upton <oliver.upton@...ux.dev>, Joey Gouly <joey.gouly@....com>,
 Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu
 <yuzenghui@...wei.com>, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>, leo.yan@....com
Subject: Re: [PATCH v3 02/10] perf: arm_spe: Support FEAT_SPEv1p4 filters



On 12/06/2025 8:35 am, Anshuman Khandual wrote:
> On 05/06/25 4:19 PM, James Clark wrote:
>> FEAT_SPEv1p4 (optional from Armv8.8) adds some new filter bits, so
>> remove them from the previous version's RES0 bits using
>> PMSEVFR_EL1_RES0_V1P4_EXCL. It also makes some previously available bits
>> unavailable again, so add those back using PMSEVFR_EL1_RES0_V1P4_INCL.
> 
> Just wondering - why cannot all the new applicable filter bits be added
> explicitly for PMSEVFR_EL1_RES0_V1P4 without using exclude and include
> intermediaries.
> 

They could but there would be a lot of duplication. Each version tended 
to add only a few bits to the previous version. Also for consistency, 
they were already defined in this way. I didn't think there was much to 
gain by redefining the whole bitset just for this one, it's probably 
going to look just as messy.

>> E.g:
>>
>>    E[30], bit [30]
>>    When FEAT_SPEv1p4 is _not_ implemented ...
>>
>> FEAT_SPE_V1P3 has the same filters as V1P2 so explicitly add it to the
>> switch.
> A small nit - should FEAT_SPE_V1P3 addition be done in a previous patch
> as it is an already existing thing ?
> 

It's related to this patch because I change the default case. Before 
V1P3 hits 'default:' and returns PMSEVFR_EL1_RES0_V1P2. But now the 
highest supported is PMSEVFR_EL1_RES0_V1P4 for the default case so I 
need to add a case for V1P3 to keep it returning PMSEVFR_EL1_RES0_V1P2 
filters. There's no bug.

>>
>> Reviewed-by: Leo Yan <leo.yan@....com>
>> Tested-by: Leo Yan <leo.yan@....com>
>> Signed-off-by: James Clark <james.clark@...aro.org>
>> ---
>>   arch/arm64/include/asm/sysreg.h | 7 +++++++
>>   drivers/perf/arm_spe_pmu.c      | 5 ++++-
>>   2 files changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
>> index f1bb0d10c39a..880090df3efc 100644
>> --- a/arch/arm64/include/asm/sysreg.h
>> +++ b/arch/arm64/include/asm/sysreg.h
>> @@ -358,6 +358,13 @@
>>   	(PMSEVFR_EL1_RES0_IMP & ~(BIT_ULL(18) | BIT_ULL(17) | BIT_ULL(11)))
>>   #define PMSEVFR_EL1_RES0_V1P2	\
>>   	(PMSEVFR_EL1_RES0_V1P1 & ~BIT_ULL(6))
>> +#define PMSEVFR_EL1_RES0_V1P4_EXCL \
>> +	(BIT_ULL(2) | BIT_ULL(4) | GENMASK_ULL(10, 8) | GENMASK_ULL(23, 19))
>> +#define PMSEVFR_EL1_RES0_V1P4_INCL \
>> +	(GENMASK_ULL(31, 26))> +#define PMSEVFR_EL1_RES0_V1P4	\
>> +	(PMSEVFR_EL1_RES0_V1P4_INCL | \
>> +	(PMSEVFR_EL1_RES0_V1P2 & ~PMSEVFR_EL1_RES0_V1P4_EXCL))
>>   
>>   /* Buffer error reporting */
>>   #define PMBSR_EL1_FAULT_FSC_SHIFT	PMBSR_EL1_MSS_SHIFT
>> diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
>> index 3efed8839a4e..d9f6d229dce8 100644
>> --- a/drivers/perf/arm_spe_pmu.c
>> +++ b/drivers/perf/arm_spe_pmu.c
>> @@ -701,9 +701,12 @@ static u64 arm_spe_pmsevfr_res0(u16 pmsver)
>>   	case ID_AA64DFR0_EL1_PMSVer_V1P1:
>>   		return PMSEVFR_EL1_RES0_V1P1;
>>   	case ID_AA64DFR0_EL1_PMSVer_V1P2:
>> +	case ID_AA64DFR0_EL1_PMSVer_V1P3:
>> +		return PMSEVFR_EL1_RES0_V1P2;
>> +	case ID_AA64DFR0_EL1_PMSVer_V1P4:
>>   	/* Return the highest version we support in default */
>>   	default:
>> -		return PMSEVFR_EL1_RES0_V1P2;
>> +		return PMSEVFR_EL1_RES0_V1P4;
>>   	}
>>   }
>>   
>>
> 
> 
> 
>