[RFC PATCH v4 20/26] KVM: arm64: Trap disabled features of ID_AA64PFR0_EL1

[Fuad Tabba]

Hi Reiji,

...

> > > +static void feature_amu_trap_activate(struct kvm_vcpu *vcpu)
> > > +{
> > > +       feature_trap_activate(vcpu, VCPU_CPTR_EL2, CPTR_EL2_TAM, 0);
> >
> > Covers the CPTR flags for AMU, but as you mentioned, does not
> > explicitly clear HCR_AMVOFFEN.
>
> In my understanding, clearing HCR_EL2.AMVOFFEN is not necessary as
> CPTR_EL2.TAM == 1 traps the guest's accessing AMEVCNTR0<n>_EL0 and
> AMEVCNTR1<n>_EL0 anyway (HCR_EL2.AMVOFFEN doesn't matter).
> (Or is my understanding wrong ??)

You're right. However, I think they should be cleared first for
completeness. Also, if I understand correctly, AMVOFFEN is about
enabling and disabling virtualization of the registers, making
indirect reads of the virtual offset registers as zero, so it's not
just about trapping.

Thanks,
/fuad

> Thanks,
> Reiji