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

On 25.02.2012, at 00:40, Scott Wood wrote:

On 02/24/2012 08:26 AM, Alexander Graf wrote:

quoted

+static void kvmppc_fill_pt_regs(struct kvm_vcpu *vcpu, struct =

pt_regs *regs)

quoted

{
-	int r =3D RESUME_HOST;
+	int i;
=20
-	/* update before a new last_exit_type is rewritten */
-	kvmppc_update_timing_stats(vcpu);
+	for (i =3D 0; i < 32; i++)
+		regs->gpr[i] =3D kvmppc_get_gpr(vcpu, i);
+	regs->nip =3D vcpu->arch.pc;
+	regs->msr =3D vcpu->arch.shared->msr;
+	regs->ctr =3D vcpu->arch.ctr;
+	regs->link =3D vcpu->arch.lr;
+	regs->xer =3D kvmppc_get_xer(vcpu);
+	regs->ccr =3D kvmppc_get_cr(vcpu);
+	regs->dar =3D get_guest_dear(vcpu);
+	regs->dsisr =3D get_guest_esr(vcpu);
+}

=20
How much overhead does this add to every interrupt?  Can't we keep =

this

to the minimum that perf cares about?

I would rather not make assumptions on what perf cares about - maybe we =
want to one day implement "perf kvm" and then perf could rely on pretty =
much anything in there.

=20

quoted

+
+static void kvmppc_restart_interrupt(struct kvm_vcpu *vcpu,
+				     unsigned int exit_nr)
+{
+	struct pt_regs regs =3D *current->thread.regs;
=20
+	kvmppc_fill_pt_regs(vcpu, &regs);

=20
Why are you copying out of current->thread.regs?  That's old junk =

data,

set by some previous exception and possibly overwritten since.

Because it gives us good default values for anything we don't set. Do =
you have other recommendations?


Alex