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Sun, 07 Jan 2024 11:37:41 +0000 Date: Sun, 07 Jan 2024 11:37:41 +0000 Message-ID: <86cyud9xx6.wl-maz@kernel.org> From: Marc Zyngier To: Oliver Upton 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) In-Reply-To: References: <20240105213251.4141-1-ilkka@os.amperecomputing.com> <87sf3au0bu.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/29.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: oliver.upton@linux.dev, ilkka@os.amperecomputing.com, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, gshan@redhat.com, mark.rutland@arm.com, rananta@google.com, scott@os.amperecomputing.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240107_033755_760920_6ABADD1B X-CRM114-Status: GOOD ( 26.18 ) 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, 06 Jan 2024 17:50:23 +0000, Oliver Upton wrote: > > 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 Huh. That's full of... not a lot. > > 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. Indeed. The document you quoted acknowledges that there are issues (one step up from the previous situation), but this is not enough to independently develop a workaround that will survive the test of time. For example, AC03_CPU_39 doesn't even list the failing encodings, which may lead to real funnies if these encodings get used at some point. M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel