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From: Oliver Upton To: Marc Zyngier Cc: Ilkka Koskinen , James Morse , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Gavin Shan , Mark Rutland , Raghavendra Rao Ananta , D Scott Phillips , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] KVM: arm64: Workaround for Ampere AC03_CPU_36 (exception taken to an incorrect EL) Message-ID: References: <20240105213251.4141-1-ilkka@os.amperecomputing.com> <87sf3au0bu.wl-maz@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <87sf3au0bu.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-20240106_095032_842178_3AB3C41C X-CRM114-Status: GOOD ( 18.43 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sat, Jan 06, 2024 at 12:13:09PM +0000, Marc Zyngier wrote: [...] > > From 265cb193190c13c651d8e008d34d1d18505d4804 Mon Sep 17 00:00:00 2001 > > From: Oliver Upton > > Date: Fri, 5 Jan 2024 23:18:14 +0000 > > Subject: [PATCH] KVM: arm64: Mitigate AmpereOne erratum AC03_CPU_36 > > > > The AmpereOne design suffers from an erratum where if an asynchronous > > exception arrives while EL2 is modifying hypervisor exception controls > > (i.e. HCR_EL2, SCTLR_EL2) the PE may take an invalid exception to > > another EL. > > Same questions about SCTLR_EL2 and the notion of "another EL". I've got the same questions :) This is just a rewording of Ampere's erratum description. https://amperecomputing.com/customer-connect/products/AmpereOne-device-documentation > Other than the passing comments, I'm OK with this patch. However, I am > very worried that this is only the start of a very long game of > whack-a-mole, because there is no actual documentation on what goes > wrong. > > For example, we have plenty of writes to SCTLR_EL2 (using the > SCTLR_EL1 alias if running VHE) for MTE. Are any of those affected? > > Short of having some solid handle on what is happening, I don't see > how we can promise to support this system. Completely agree. At least on the AmpereOne machines I have access to this seems to do the trick, but that observation is no replacement for full documentation. -- Thanks, Oliver _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel