linux-kernel - Re: [PATCH v3 03/22] KVM: arm64: Define PMI{CNTR,FILTR}_EL0 as undef

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Message-ID: <gsntcyao9am8.fsf@coltonlewis-kvm.c.googlers.com>
Date: Fri, 27 Jun 2025 20:45:51 +0000
From: Colton Lewis <coltonlewis@...gle.com>
To: Marc Zyngier <maz@...nel.org>
Cc: kvm@...r.kernel.org, pbonzini@...hat.com, corbet@....net, 
	linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org, 
	oliver.upton@...ux.dev, mizhang@...gle.com, joey.gouly@....com, 
	suzuki.poulose@....com, yuzenghui@...wei.com, mark.rutland@....com, 
	shuah@...nel.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	linux-perf-users@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 03/22] KVM: arm64: Define PMI{CNTR,FILTR}_EL0 as undef_access

Hi Marc. Thanks for the review.

Marc Zyngier <maz@...nel.org> writes:

> On Thu, 26 Jun 2025 21:04:39 +0100,
> Colton Lewis <coltonlewis@...gle.com> wrote:

>> Because KVM isn't fully prepared to support these yet even though the
>> host PMUv3 driver does, define them as undef_access for now.

>> Signed-off-by: Colton Lewis <coltonlewis@...gle.com>
>> ---
>>   arch/arm64/kvm/sys_regs.c | 3 +++
>>   1 file changed, 3 insertions(+)

>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index 76c2f0da821f..99fdbe174202 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -3092,6 +3092,9 @@ static const struct sys_reg_desc sys_reg_descs[] =  
>> {
>>   	{ SYS_DESC(SYS_SVCR), undef_access, reset_val, SVCR, 0, .visibility =  
>> sme_visibility  },
>>   	{ SYS_DESC(SYS_FPMR), undef_access, reset_val, FPMR, 0, .visibility =  
>> fp8_visibility },

>> +	{ SYS_DESC(SYS_PMICNTR_EL0), undef_access },

> $ jq -r --arg FEAT "FEAT_PMUv3_ICNTR" -f ./dumpfeat.jq Features.json
> (FEAT_PMUv3_ICNTR --> v8Ap8)
> (FEAT_PMUv3_ICNTR --> FEAT_PMUv3p9)
> ((FEAT_PMUv3_ICNTR && FEAT_AA64EL2) --> FEAT_FGT2)

> If you have FEAT_PMUv3_ICNTR, then you have FEAT_FGT2. If you have
> FEAT_FGT2, then we already trap and UNDEF PMICNTR_EL0 without any
> further handling since 4bc0fe0898406 ("KVM: arm64: Add sanitisation
> for FEAT_FGT2 registers").

>> +	{ SYS_DESC(SYS_PMICFILTR_EL0), undef_access },

> Same thing.
>> +
>>   	{ PMU_SYS_REG(PMCR_EL0), .access = access_pmcr, .reset = reset_pmcr,
>>   	  .reg = PMCR_EL0, .get_user = get_pmcr, .set_user = set_pmcr },
>>   	{ PMU_SYS_REG(PMCNTENSET_EL0),

> So none of this is actually required.

Thanks for the context. I'll take this patch out.