Re: [PATCH 36/37] KVM: PPC: booke: expose guest registers on irq reinject

[Scott Wood]

On 02/24/2012 08:26 AM, Alexander Graf wrote:
> +static void kvmppc_fill_pt_regs(struct kvm_vcpu *vcpu, struct pt_regs *regs)
>  {
> -     int r = RESUME_HOST;
> +     int i;
>  
> -     /* update before a new last_exit_type is rewritten */
> -     kvmppc_update_timing_stats(vcpu);
> +     for (i = 0; i < 32; i++)
> +             regs->gpr[i] = kvmppc_get_gpr(vcpu, i);
> +     regs->nip = vcpu->arch.pc;
> +     regs->msr = vcpu->arch.shared->msr;
> +     regs->ctr = vcpu->arch.ctr;
> +     regs->link = vcpu->arch.lr;
> +     regs->xer = kvmppc_get_xer(vcpu);
> +     regs->ccr = kvmppc_get_cr(vcpu);
> +     regs->dar = get_guest_dear(vcpu);
> +     regs->dsisr = get_guest_esr(vcpu);
> +}

How much overhead does this add to every interrupt?  Can't we keep this
to the minimum that perf cares about?

> +
> +static void kvmppc_restart_interrupt(struct kvm_vcpu *vcpu,
> +                                  unsigned int exit_nr)
> +{
> +     struct pt_regs regs = *current->thread.regs;
>  
> +     kvmppc_fill_pt_regs(vcpu, &regs);

Why are you copying out of current->thread.regs?  That's old junk data,
set by some previous exception and possibly overwritten since.

-Scott

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