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

[Marc Zyngier]

On Mon, 21 Jul 2025 13:32:08 +0100,
Cornelia Huck <cohuck at redhat.com> wrote:
> 
> On Mon, Jul 21 2025, Marc Zyngier <maz at 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?

Ah, that's an interesting point -- I definitely had glanced over that.

But I'm not sure a guest can actually distinguish between these two
configurations, given that FEAT_DoubleFault is essentially an EL3
feature (as indicated in the RAS == V1P1 section, and further
confirmed in R_GRJVN), making it invisible to the guest.

FEAT_DoubleFault2 is, on the contrary, totally visible from the guest,
and independent of EL3.

Does this make sense to you?

Thanks,

	M.

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