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

[Scott Wood <scottwood@freescale.com>]

On 07/03/2013 12:07:30 PM, Alexander Graf wrote:
> 
> On 03.07.2013, at 18:49, Caraman Mihai Claudiu-B02008 wrote:
> 
> >>>> Do we need to do this even when the guest doesn't use Altivec?  
> 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  
> KVM
> >> guest. Are we?
> >
> > Yes, because MSR[SPV] is under its control.
> 
> Oh, sure, KVM wants it unlazy. That part is obvious. But does the  
> kernel always give us unlazyness? The way I read the code, process.c  
> goes lazy when !CONFIG_SMP.
> 
> So the big question is why we're manually enforcing FPU giveup, but  
> not Altivec giveup? One of the 2 probably is wrong :).

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

-Scott