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V" , Emi Kisanuki , Vishal Annapurve , WeiLin.Chang@arm.com, Lorenzo Pieralisi Subject: Re: [PATCH v15 12/37] KVM: arm64: CCA: Support the VGIC in realms Message-ID: References: <20260715142841.80544-1-steven.price@arm.com> <20260715142841.80544-13-steven.price@arm.com> <86cxwfe5m8.wl-maz@kernel.org> <868q72dt8o.wl-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <868q72dt8o.wl-maz@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260723_020253_220205_2D8A2E8A X-CRM114-Status: GOOD ( 28.00 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 07/23 09:07, Marc Zyngier wrote: > On Thu, 23 Jul 2026 07:38:16 +0100, > Kohei Enju 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. >