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

Marc Zyngier
2025-06-27T13:31:08Z

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.