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From: Oliver Upton To: Marc Zyngier Cc: Eric Auger , Ganapatrao Kulkarni , kvmarm , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, christoffer.dall@arm.com, suzuki.poulose@arm.com, will@kernel.org, catalin.marinas@arm.com, coltonlewis@google.com, joey.gouly@arm.com, yuzenghui@huawei.com, darren@os.amperecomputing.com, vishnu@os.amperecomputing.com Subject: Re: [PATCH] KVM: arm64: nv: Set ISTATUS for emulated timers, If timer expired Message-ID: References: <86y10osr19.wl-maz@kernel.org> <4d443db1-85b1-4071-acd5-3187deb9cb17@redhat.com> <2f6b2cb1-3d32-480a-9801-9b993ae74e2d@os.amperecomputing.com> <152d262e-641d-4bb1-9656-a13e049d62c4@redhat.com> <86h661wje4.wl-maz@kernel.org> <4a9fbdd9-ad23-44bc-8ba5-399f08068db4@redhat.com> <86cygpwfy0.wl-maz@kernel.org> <86frkptzr6.wl-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <86frkptzr6.wl-maz@kernel.org> X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250207_181014_698460_132C1664 X-CRM114-Status: GOOD ( 13.57 ) 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 Hey, On Fri, Feb 07, 2025 at 05:45:33PM +0000, Marc Zyngier wrote: > I found at least one issue that could fail the migration. Before the > VM starts running, we limit the feature set to the subset we actually > support with NV. > > By doing this, we also change the value of IDreg fields that are not > writable, because they describe features that we don't support. > Obviously, that fails on restore. > > I need to have a think... We spoke about this a while ago (and I forgot til now), but I was wondering if we could use vCPU feature flags to describe NV, including the selection between FEAT_E2H0 and FEAT_VHE. I think this might match userspace expectations a bit more closely where the state of the ID registers after init gives the actual feature set supported by the VM. -- Thanks, Oliver