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

[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:
> >> > +    if (opp->mpic_mode_mask == GCR_MODE_PROXY)
> >> Shouldn't this be an &?
> >
> > The way the mode field was originally documented was a two-bit  
> field, where 0b11 was external proxy, and 0b10 was reserved.  If we  
> use & it would have to be:
> >
> >    if ((opp->mpic_mode_mask & GCR_MODE_PROXY) == GCR_MODE_PROXY)
> >        ...
> >
> > Simply testing "opp->mpic_mode_mask & GCR_MODE_PROXY" would return  
> true in the case of GCR_MODE_MIXED.
> >
> > In MPIC 4.3 external proxy is defined as a separate bit (GCR[CI])  
> that is ignored if the mixed-mode bit (GCR[M]) is not set, which  
> makes it a bit more legitimate to view it as a bitmap.  Still, I  
> doubt we'll see new mode bits.
> 
> Ok, please add a comment about this here then :).

What sort of comment would you like?  Or do you want me to use the "(x  
& y) == y" version?

> >> > @@ -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.

-Scott