linux-kernel - Re: [PATCH v3 04/10] arm64/boot: Enable EL2 requirements for SPE_FEAT

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Message-ID: <04d52182-6043-4eaf-a898-9f8ccc893e5f@linaro.org>
Date: Tue, 15 Jul 2025 13:48:03 +0100
From: James Clark <james.clark@...aro.org>
To: Will Deacon <will@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
 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,
 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
Subject: Re: [PATCH v3 04/10] arm64/boot: Enable EL2 requirements for
 SPE_FEAT_FDS



On 14/07/2025 2:54 pm, Will Deacon wrote:
> On Thu, Jun 05, 2025 at 11:49:02AM +0100, James Clark wrote:
>> SPE data source filtering (optional from Armv8.8) requires that traps to
>> the filter register PMSDSFR be disabled. Document the requirements and
>> disable the traps if the feature is present.
>>
>> Tested-by: Leo Yan <leo.yan@....com>
>> Signed-off-by: James Clark <james.clark@...aro.org>
>> ---
>>   Documentation/arch/arm64/booting.rst | 11 +++++++++++
>>   arch/arm64/include/asm/el2_setup.h   | 14 ++++++++++++++
>>   2 files changed, 25 insertions(+)
>>
>> diff --git a/Documentation/arch/arm64/booting.rst b/Documentation/arch/arm64/booting.rst
>> index dee7b6de864f..abd75085a239 100644
>> --- a/Documentation/arch/arm64/booting.rst
>> +++ b/Documentation/arch/arm64/booting.rst
>> @@ -404,6 +404,17 @@ Before jumping into the kernel, the following conditions must be met:
>>       - HDFGWTR2_EL2.nPMICFILTR_EL0 (bit 3) must be initialised to 0b1.
>>       - HDFGWTR2_EL2.nPMUACR_EL1 (bit 4) must be initialised to 0b1.
>>   
>> +  For CPUs with SPE data source filtering (FEAT_SPE_FDS):
>> +
>> +  - If EL3 is present:
>> +
>> +    - MDCR_EL3.EnPMS3 (bit 42) must be initialised to 0b1.
>> +
>> +  - If the kernel is entered at EL1 and EL2 is present:
>> +
>> +    - HDFGRTR2_EL2.nPMSDSFR_EL1 (bit 19) must be initialised to 0b1.
>> +    - HDFGWTR2_EL2.nPMSDSFR_EL1 (bit 19) must be initialised to 0b1.
>> +
>>     For CPUs with Memory Copy and Memory Set instructions (FEAT_MOPS):
>>   
>>     - If the kernel is entered at EL1 and EL2 is present:
>> diff --git a/arch/arm64/include/asm/el2_setup.h b/arch/arm64/include/asm/el2_setup.h
>> index 1e7c7475e43f..02b4a7fc016e 100644
>> --- a/arch/arm64/include/asm/el2_setup.h
>> +++ b/arch/arm64/include/asm/el2_setup.h
>> @@ -279,6 +279,20 @@
>>   	orr	x0, x0, #HDFGRTR2_EL2_nPMICFILTR_EL0
>>   	orr	x0, x0, #HDFGRTR2_EL2_nPMUACR_EL1
>>   .Lskip_pmuv3p9_\@:
>> +	mrs	x1, id_aa64dfr0_el1
>> +	ubfx	x1, x1, #ID_AA64DFR0_EL1_PMSVer_SHIFT, #4
>> +	/* If SPE is implemented, */
>> +	cmp	x1, #ID_AA64DFR0_EL1_PMSVer_IMP
>> +	b.lt	.Lskip_spefds_\@
>> +	/* we can read PMSIDR and */
>> +	mrs_s	x1, SYS_PMSIDR_EL1
>> +	and	x1, x1,  #PMSIDR_EL1_FDS
>> +	/* if FEAT_SPE_FDS is implemented, */
>> +	cbz	x1, .Lskip_spefds_\@
>> +	/* disable traps to PMSDSFR. */
>> +	orr	x0, x0, #HDFGRTR2_EL2_nPMSDSFR_EL1
> 
> Why is this being done here rather than alongside the existing SPE
> configuration of HDFGRTR_EL2 and HDFGWTR_EL2 near the start of
> __init_el2_fgt?
> 
> Will

I thought everything was separated by which trap configs it writes to, 
rather than the feature. This SPE feature is in HDFGRTR2 so I put it in 
__init_el2_fgt2 rather than __init_el2_fgt.

I suppose we could have a single __init_el2_spe that writes to both 
HDFGRTR and HDFGRTR2 but we'd have to be careful to not overwrite what 
was already done in the other sections.