On Mon, Jul 21 2025, Marc Zyngier <maz@xxxxxxxxxx> wrote: > On Mon, 21 Jul 2025 13:32:08 +0100, > Cornelia Huck <cohuck@xxxxxxxxxx> wrote: >> >> On Mon, Jul 21 2025, Marc Zyngier <maz@xxxxxxxxxx> 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? It does; but it might make sense to add a comment explaining that. Userspace should hopefully be able to just map everything to RAS == V1P1 and be done with it.
