Re: [PATCH v15 12/37] KVM: arm64: CCA: Support the VGIC in realms

[Kohei Enju]

On 07/23 09:07, Marc Zyngier wrote:
> On Thu, 23 Jul 2026 07:38:16 +0100,
> Kohei Enju <enju.kohei@xxxxxxxxxxx> wrote:
> > 
> > On 07/22 10:27, Marc Zyngier wrote:
> > > >
> > > > As far as I can tell, the CCA requirements don't require the
> > > > ARM64_HAS_ICH_HCR_EL2_TDIR feature. If that's the case, this seems to be a
> > > > problem. Is there any workaround for this issue, or should we implement trap
> > > > handlers for those registers?
> > > 
> > > No. Either you support TDIR, like any modern CPU, or you don't run
> > > CCA. I'm not adding yet another level of emulation for this.
> > 
> > However, I'm still not aware of any requirement in the CCA architecture,
> > or in Armv8-A/Armv9-A, that mandates TDIR support.
> 
> The GICv3 architecture has deprecated the lack of TDIR support since
> the very first release of the specification in 2015, because it was
> quickly identified as an architecture bug. CCA mandates GICv3 support
> as written in the spec, and relying on deprecated features 11 years
> later is not acceptable.
> 
> By any definition, this is buggy hardware, and I don't feel a strong
> urge to support it.
> 
> > 
> > When you say "you don't run CCA", is that because the architecture
> > requires it,
> 
> See above.
> 
> > or because that's the current KVM policy? If it's the
> > latter, we'd be interested in adding the required emulation to make it
> > work.
> 
> And I say no to this. Enough. This isn't a "policy*. This is a hard
> red line. "Do Not Cross".
> 
> We already have the most complicated interrupt architecture ever, and
> I have zero desire to add even more complexity to it. Because I'm the
> idiot who ends-up maintaining this horror, and not you.
> 
> So no, no more emulation code. CCA in KVM won't handle systems that do
> not support TDIR, unless you rewrite the CCA support so that it can
> use the *existing* emulation code without any change.

Understood. Thanks for the clarification.

Thanks,
Kohei

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