[libvirt] ARM KVM GICv3 Support

[Christoffer Dall]

On Wed, Jan 06, 2016 at 01:30:16PM +0000, Peter Maydell wrote:
> On 6 January 2016 at 12:49, Andrea Bolognani <abologna at redhat.com> wrote:
> > That's correct, having a QMP command that lists the values gic-version
> > can have on the current host would be just great.
> >
> > If we had that, we could validate the GIC version chosen for a guest,
> > and expose it in the capabilities XML so that higher-level tools can
> > provide a list of choices to the user.
> >
> > Please note that this QMP command would have to work regardless of the
> > machine type selected on QEMU's command line, because libvirt always
> > runs a QEMU binary with '-M none' when probing its capabilities.
> 
> On the other hand, if you don't tell us the machine type you care
> about then we can't tell you:
>  (a) "this machine type doesn't support setting this property at all"
>      (which applies to machines like vexpress-a15 which you can use with
>      KVM on 32-bit hosts, and of course also to all the non-KVM models)
>  (b) "this machine type only supports GIC versions X and Y even if the
>       host supports more" (this is currently only hypothetical, though,
>       since we only have the property on 'virt'. it would only happen
>       if in the future we needed something other than '2' or '3' or
>       'host' I think.)
> 
> If you use -M none then we can only tell you information you
> could have got yourself by directly asking the kernel about it.
> 
So where does this leave us?  Do we need a QMP command or not?

It sounds to me like we should implement one, and the answer depends on
the machine option chosen, where -M none gives you the generic
capabilities of the kernel and for other machines it tells you what's
possible?

Thanks,
-Christoffer