Re: [RFC PATCH 2/5] hw/intc/gicv3: add support for setting KVM vGIC maintenance IRQ

[Marc Zyngier]

On Mon, 06 Mar 2023 14:02:33 +0000,
Peter Maydell <peter.maydell@linaro.org> wrote:
> 
> On Mon, 27 Feb 2023 at 16:37, Miguel Luis <miguel.luis@oracle.com> wrote:
> >
> > From: Haibo Xu <haibo.xu@linaro.org>
> >
> > Use the VGIC maintenance IRQ if VHE is requested. As per the ARM GIC
> > Architecture Specification for GICv3 and GICv4 Arm strongly recommends that
> > maintenance interrupts are configured to use INTID 25 matching the
> > Server Base System Architecture (SBSA) recomendation.
> 
> What does this mean for QEMU, though? If the issue is
> "KVM doesn't support the maintenance interrupt being anything
> other than INTID 25" then we should say so (and have our code
> error out if the board tries to use some other value).

No, KVM doesn't give two hoots about the INTID, as long as this is a
PPI that is otherwise unused.

> If the
> issue is "the *host* has to be using the right INTID" then I
> would hope that KVM simply doesn't expose the capability if
> the host h/w won't let it work correctly.

No host maintenance interrupt, no NV. This is specially mandatory as
the L1 guest is in (almost) complete control of the ICH_*_EL2
registers and expects MIs to be delivered.

> If KVM can happily
> use any maintenance interrupt ID that the board model wants,
> then we should make that work, rather than hardcoding 25 into
> our gicv3 code.

+1.

I'd eliminate any reference to SBSA, as it has no bearing on either
KVM nor the QEMU GIC code.

I also question the "if VHE is requested". Not having VHE doesn't
preclude virtualisation. Was that supposed to be "virtualisation
extension" instead?

Thanks,

        M.

-- 
Without deviation from the norm, progress is not possible.