On Mon, 4 Apr 2011 17:01:31 +0200
Alexander Graf <agraf@xxxxxxx> wrote:
> On 04/01/2011 09:17 PM, Scott Wood wrote:
> > diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
> > index 5120a63..4d39f2d 100644
> > --- a/arch/powerpc/kernel/asm-offsets.c
> > +++ b/arch/powerpc/kernel/asm-offsets.c
> > @@ -494,6 +494,12 @@ int main(void)
> > DEFINE(TLBCAM_MAS3, offsetof(struct tlbcam, MAS3));
> > DEFINE(TLBCAM_MAS7, offsetof(struct tlbcam, MAS7));
> > #endif
> > +#ifdef CONFIG_SPE
>
> if defined(CONFIG_KVM) && defined(CONFIG_SPE)
Right.
> > +static void kvmppc_vcpu_sync_spe(struct kvm_vcpu *vcpu)
> > +{
> > + if (vcpu->arch.shared->msr& MSR_SPE) {
> > + if (!(vcpu->arch.shadow_msr& MSR_SPE))
> > + kvmppc_vcpu_enable_spe(vcpu);
> > + } else if (vcpu->arch.shadow_msr& MSR_SPE) {
> > + kvmppc_vcpu_disable_spe(vcpu);
>
> So what if shared->msr & MSR_SPE && shadow_msr & MSR_SPE? Do you disable
> it then?
No.
The only times it should get disabled are if the guest clears its MSR_SPE,
or from kvmppc_core_vcpu_put().
If you're saying you think this code does so by accident, I don't see it --
the disable call is in an else branch that ensures !(shared->msr & MSR_SPE).
> > +#ifdef CONFIG_SPE
> > +_GLOBAL(kvmppc_save_guest_spe)
> > + cmpi 0,r3,0
> > + beqlr-
> > + addi r5,r3,VCPU_EVR
> > + SAVE_32EVRS(0, r4, r5, 0)
Hmm, I missed VCPU_EVR here, it can be directly passed to SAVE_32EVRS now.
> > + evxor evr6, evr6, evr6
> > + evmwumiaa evr6, evr6, evr6
> > + li r4,VCPU_ACC
> > + evstddx evr6, r4, r3 /* save acc */
>
> I'm not sure I fully understand SPE instructions yet, but isn't evr6
> just r6 plus its upper 32 bits?
Yes.
> Then wouldn't it make sense to work in evr3/evr4 and only copy the
> upper 32 bits over to another register? Not that it should matter -
> I'm only being curious here :)
We need to save the whole thing -- evr6 holds the accumulator at that
point (produced by the preceding evxor+evwmumiaa), not a regular EVR
whose lower half has already been saved. evstddx is the easiest way to
do that.
-Scott
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