Re: [Qemu-devel] [libvirt] [RFC PATCH 0/2] ARM: add QMP command to query GIC version

[Andrew Jones]

On Mon, Feb 15, 2016 at 09:41:57AM +0000, Peter Maydell wrote:
> On 15 February 2016 at 09:35, Martin Kletzander <address@hidden> wrote:
> > So hardware itself supports some GIC version, let's say 3 for our case.
> > Does that mean it can be triggered to do v2 as well?  I mean is it
> > possible that HW supports multiple versions?  If yes, then I suspect
> > there is (will be) HW that does *not* do it
> 
> Hardware may be:
>  GICv2 only
>  GICv3 only
>  GICv3 with v2 backwards-compatibility support
> 
> > and that's where QEMU (or
> > KVM) must emulate that version.
> 
> If the hardware doesn't support the version that we are trying
> to provide to the guest then we can't run KVM at all. (KVM
> with an emulated interrupt controller is not a supported setup,
> because you wouldn't get CPU timer interrupts in the guest.)

I know Pavel Fedin was trying to revive kernel_irqchip=off once,
but I don't know if that effort was abandoned or not. I think it
could be a nice-to-have, in order to help isolate bugs with KVM,
but I agree running that way wouldn't be the norm.

Thanks,
drew