Subject: Re: [PATCH 2/6] KVM: PPC: Book3E: Refactor SPE/FP exit handling

From: Scott Wood <[email-masked]>
Date: Wed, 3 Jul 2013 13:28:59 -0500

On 07/03/2013 10:13:57 AM, Alexander Graf wrote:
>=20
> On 03.07.2013, at 15:53, Caraman Mihai Claudiu-B02008 wrote:
>=20
> >>> -#ifdef CONFIG_SPE
> >>> 	case BOOKE_INTERRUPT_SPE_ALTIVEC_UNAVAIL: {
> >>> -		if (vcpu->arch.shared->msr & MSR_SPE)
> >>> -			kvmppc_vcpu_enable_spe(vcpu);
> >>> -		else
> >>> -			kvmppc_booke_queue_irqprio(vcpu,
> >>> -
> >> BOOKE_IRQPRIO_SPE_ALTIVEC_UNAVAIL);
> >>> +		if (kvmppc_supports_spe()) {
> >>> +			bool enabled =3D false;
> >>> +
> >>> +#ifndef CONFIG_KVM_BOOKE_HV
> >>> +			if (vcpu->arch.shared->msr & MSR_SPE) {
> >>> +				kvmppc_vcpu_enable_spe(vcpu);
> >>> +				enabled =3D true;
> >>> +			}
> >>> +#endif
> >>
> >> Why the #ifdef? On HV capable systems kvmppc_supports_spe() will =20
> just
> >> always return false.
> >
> > AltiVec and SPE unavailable exceptions follows the same path. While
> > kvmppc_supports_spe() will always return false =20
> kvmppc_supports_altivec()
> > may not.
>=20
> There is no chip that supports SPE and HV at the same time. So we'll =20
> never hit this anyway, since kvmppc_supports_spe() always returns =20
> false on HV capable systems.
>=20
> Just add a comment saying so and remove the ifdef :).

kvmppc_vcpu_enable_spe isn't defined unless CONFIG_SPE is defined.  =20
More seriously, MSR_SPE is the same as MSR_VEC, so we shouldn't =20
interpret it as SPE unless CONFIG_SPE is defined.  And we can't rely on =20
the "if (kvmppc_supports_spe())" here because a later patch changes it =20
to "if (kvmppc_supports_altivec() || kvmppc_supports_spe())".  So I =20
think we still need the ifdef CONFIG_SPE here.

As for the HV ifndef, we should try not to confuse HV/PR with =20
e500mc/e500v2, even if we happen to only run HV on e500mc and PR on =20
e500v2.  We would not want to call kvmppc_vcpu_enable_spe() here on a =20
hypothetical HV target with SPE.  And we *would* want to call =20
kvmppc_vcpu_enable_fp() here on a hypothetical PR target with normal =20
FP.  It's one thing to leave out the latter, since it would involve =20
writing actual code that we have no way to test at this point, but =20
quite another to leave out the proper conditions for when we want to =20
run code that we do have.

-Scott=