Subject: Re: [PATCH 4/6] KVM: PPC: Book3E: Add AltiVec support

From: Scott Wood <[email-masked]>
Date: Wed, 3 Jul 2013 13:36:15 -0500

On 07/03/2013 12:07:30 PM, Alexander Graf wrote:
>=20
> On 03.07.2013, at 18:49, Caraman Mihai Claudiu-B02008 wrote:
>=20
> >>>> Do we need to do this even when the guest doesn't use Altivec? =20
> Can't
> >> we
> >>>> just load it on demand then once we fault? This code path really
> >> should
> >>>> only be a prefetch enable when MSR_VEC is already set in guest
> >> context.
> >>>
> >>> No we can't, read 6/6.
> >>
> >> So we have to make sure we're completely unlazy when it comes to a =20
> KVM
> >> guest. Are we?
> >
> > Yes, because MSR[SPV] is under its control.
>=20
> Oh, sure, KVM wants it unlazy. That part is obvious. But does the =20
> kernel always give us unlazyness? The way I read the code, process.c =20
> goes lazy when !CONFIG_SMP.
>=20
> So the big question is why we're manually enforcing FPU giveup, but =20
> not Altivec giveup? One of the 2 probably is wrong :).

Why do you think we're not enforcing it for Altivec?  Is there some =20
specific piece of code you're referring to that is different in this =20
regard?

-Scott=