[v3] ARM64 PMU Partitioning

[PATCH v3 03/22] KVM: arm64: Define PMI{CNTR,FILTR}_EL0 as undef_access

Posted by Colton Lewis 3 months, 1 week ago

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@google.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 },
+	{ SYS_DESC(SYS_PMICFILTR_EL0), undef_access },
+
 	{ 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),
-- 
2.50.0.727.gbf7dc18ff4-goog

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

Posted by Marc Zyngier 3 months, 1 week ago

On Thu, 26 Jun 2025 21:04:39 +0100,
Colton Lewis <coltonlewis@google.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@google.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.

	M.

-- 
Without deviation from the norm, progress is not possible.

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

Posted by Colton Lewis 3 months, 1 week ago

Hi Marc. Thanks for the review.

Marc Zyngier <maz@kernel.org> writes:

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