Re: [PATCH 0/1] x2apic implementation for kvm

[Gleb Natapov <gleb@redhat.com>]

On Mon, May 25, 2009 at 02:08:26PM +0800, Sheng Yang wrote:
> On Friday 22 May 2009 01:37:53 Gleb Natapov wrote:
> > This is implementation of x2apic for KVM that I wrote a while ago.
> > Unfortunately there is no guest that can take advantage of it since
> > Linux doesn't (yet?) use x2apic if interrupt remapping is not enabled
> > and I don't feel like implement interrupt remapping device :)
> >
> > Re-based to latest kvm tree for your viewing pleasure and feedback.
> 
> Yeah... x2apic is for interrupt remapping, and interrupt remapping is for VT-d 
> engine. So if we don't want to virtualize VT-d engine and interrupt remapping, 
> x2apic is useless for the guest... And VT-d engine(and related things) 
> virtualization is far from our scope now...
> 
Can you explain why "x2apic is for interrupt remapping"? I can understand
why interrupt remapping is needed to use x2apic in certain circumstances
(apic ids > 256). x2apic has better virtualizable interface and that
is why we want to emulate it. Can you name one technical reason why it
can't be done in a context of KVM?

--
			Gleb.