Re: [RFC PATCH v3 6/6] kvm/ppc/mpic: add KVM_CAP_IRQ_MPIC

Scott Wood
2013-04-05T17:12:06Z

On 04/05/2013 01:09:50 AM, Alexander Graf wrote:
>
>
> Am 05.04.2013 um 00:35 schrieb Scott Wood <scottwood@freescale.com>:
>
> > On 04/04/2013 05:30:05 PM, Alexander Graf wrote:
> >> Am 04.04.2013 um 20:41 schrieb Scott Wood
> <scottwood@freescale.com>:
> >> > On 04/04/2013 07:54:20 AM, Alexander Graf wrote:
> >> >> On 03.04.2013, at 03:57, Scott Wood wrote:
> >> >> > @@ -460,6 +464,13 @@ void kvm_arch_vcpu_free(struct kvm_vcpu
> *vcpu)
> >> >> > tasklet_kill(&vcpu->arch.tasklet);
> >> >> >
> >> >> > kvmppc_remove_vcpu_debugfs(vcpu);
> >> >> > +
> >> >> > + switch (vcpu->arch.irq_type) {
> >> >> > + case KVMPPC_IRQ_MPIC:
> >> >> > + kvmppc_mpic_put(vcpu->arch.mpic);
> >> >> This doesn't tell the MPIC that this exact CPU is getting
> killed. What if we hotplug remove just a single CPU? Don't we have to
> deregister the CPU with the MPIC?
> >> >
> >> > If we ever support hot vcpu removal, yes. We'd probably need
> some MPIC code changes to accommodate that, and we wouldn't currently
> have a way to test it, so I'd rather make it obviously not supported
> for now.
> >> Is there any way to break heavily if user space attempts this?
> >
> > Is there any way for userspace to request this currently? They can
> close the vcpu fd, but the vcpu won't actually be destroyed until the
> vm goes down.
>
> Are you sure? X86 does CPU hotplug today, so there has to be
> something :)

Hot add, or hot remove?

Can you give me any hint on where to look?

kvm_cpu_hotplug() appears to deal with hotplug of *physical* cpus --
and is currently a no-op on powerpc. Other than that, grepping isn't
turning up much.

-Scott