Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index

[Eduardo Habkost]

On Wed, Jun 14, 2017 at 03:17:54PM +0200, Paolo Bonzini wrote:
> 
> 
> On 14/06/2017 15:11, Igor Mammedov wrote:
> >> No, KVM really uses the VCPU _index_ for HV_X64_MSR_VP_INDEX:
> >
> > and as you pointed out that works just by luck,
> > as soon as we there would be out of order created CPUs
> > returned value won't match cpu_index.
> > 
> > So instead of spreading this nonsense out to QEMU, is it possible
> > to fix kernel(kvm+guest) to use apic_id instead?
> 
> Yes, definitely.  At this point let's add a new "KVM_CAP_HYPERV_SYNIC2"
> capability and declare the old one broken, that will make things easier.

What do we need a capability for?  Can't we just call
KVM_SET_MSRS using arch_id (== apic_id) and warn the user if it
doesn't work?

-- 
Eduardo