Re: [RFC PATCH-for-9.1? 1/2] target/arm: Move qmp_query_gic_capabilities() to hw/intc/

[Peter Maydell <peter.maydell@linaro.org>]

On Thu, 8 Aug 2024 at 12:23, Daniel P. Berrangé <berrange@redhat.com> wrote:
> On Thu, Aug 08, 2024 at 11:15:17AM +0100, Peter Maydell wrote:
> > It's not possible to use KVM with that machine type, so the
> > question is a bit moot. (This also indicates that the
> > interface is not very helpful -- it purports to tell the
> > management layer whether it can use an accelerated in-kernel
> > GIC, but because it doesn't specifiy the board type there's
> > no way to provide an accurate answer. It would be useful
> > to know exactly what libvirt/etc actually use this for...)
>
> Libvirt uses this exclusively with the arm 'virt' machine type.
>
> If the user didn't express any GIC preference, then if KVM is in use,
> we'll pick the highest GIC version QEMU reports as supported.

You can get that without querying QEMU by asking for 'gic-version=max'
if you like.

> If TCG
> is in use we'll always pick v2, even if QEMU reports v3 is emulatable
> due to the v3 impl lacking MSI controller which we need for PCI-e

Our emulated GICv3 supports the ITS which has MSI support, so I'm not
sure what forcing GICv2 is getting you here. Looking at the linked
RHEL bugzilla bug, I suspect this is an out-of-date policy from before
we added the ITS emulation in 2021 (it's present by default
in virt-2.8 and later machine types). So that is something that
libvirt should update I think.

thanks
-- PMM