Re: [libvirt] [Qemu-devel] [RFC PATCH 0/2] ARM: add QMP command to query GIC version
On Mon, Feb 15, 2016 at 09:41:57AM +0000, Peter Maydell wrote:
On 15 February 2016 at 09:35, Martin Kletzander
<mkletzan(a)redhat.com> 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