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Tue, 15 Jul 2025 06:10:19 -0700 (PDT) Message-ID: Date: Tue, 15 Jul 2025 14:10:18 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 04/10] arm64/boot: Enable EL2 requirements for SPE_FEAT_FDS To: Will Deacon Cc: Catalin Marinas , Mark Rutland , Jonathan Corbet , Marc Zyngier , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , leo.yan@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev References: <20250605-james-perf-feat_spe_eft-v3-0-71b0c9f98093@linaro.org> <20250605-james-perf-feat_spe_eft-v3-4-71b0c9f98093@linaro.org> <04d52182-6043-4eaf-a898-9f8ccc893e5f@linaro.org> Content-Language: en-US From: James Clark In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 15/07/2025 1:57 pm, Will Deacon wrote: > On Tue, Jul 15, 2025 at 01:48:03PM +0100, James Clark wrote: >> >> >> 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 >>>> Signed-off-by: James Clark >>>> --- >>>> 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? >>> >> 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. > > That's fair; __init_el2_fgt isn't the right place. But the redundancy of > re-reading PMSVer from DFR0 is a little jarring. > >> 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. > > Right, perhaps it would be clearer to have trap-preserving macros for > features in a specific ID register rather than per-trap configuration > register macros. > > In other words, we have something like __init_fgt_aa64dfr0 which would > configure the FGT and FGT2 registers based on features in aa64dfr0. I > think you'd need to have a play to see how it ends up looking but the > main thing to avoid is having duplicate ID register parsing code for > setting up FGT and FGT2 traps. > > Will I'll give it a go but that could end up being fragile to something that is dependent on two different ID registers in the future. Then we'd end up in the same situation for a different reason.