Re: [PATCH 6/7] KVM: arm64: Expose FEAT_RASv1p1 in a canonical manner

[Cornelia Huck <cohuck@redhat.com>]

On Mon, Jul 21 2025, Marc Zyngier <maz@kernel.org> wrote:

> If we have RASv1p1 on the host, advertise it to the guest in the
> "canonical way", by setting ID_AA64PFR0_EL1 to V1P1, rather than
> the convoluted RAS+RAS_frac method.

Don't the two methods have slightly different semantics with RAS == V1P1
possibly implying FEAT_DoubleFault, and RAS+RAS_frac not?

>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 9fb2812106cb0..549766d7abca8 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1800,6 +1800,15 @@ static u64 sanitise_id_aa64pfr0_el1(const struct kvm_vcpu *vcpu, u64 val)
>  	if (!vcpu_has_sve(vcpu))
>  		val &= ~ID_AA64PFR0_EL1_SVE_MASK;
>  
> +	/*
> +	 * Describe RASv1p1 in a canonical way -- ID_AA64PFR1_EL1.RAS_frac
> +	 * is cleared separately.
> +	 */
> +	if (cpus_have_final_cap(ARM64_HAS_RASV1P1_EXTN)) {
> +		val &= ~ID_AA64PFR0_EL1_RAS;
> +		val |= SYS_FIELD_PREP_ENUM(ID_AA64PFR0_EL1, RAS, V1P1);
> +	}
> +
>  	/*
>  	 * The default is to expose CSV2 == 1 if the HW isn't affected.
>  	 * Although this is a per-CPU feature, we make it global because
> -- 
> 2.39.2