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[2003:f6:af28:4000:f9ca:1328:aeaa:cdd4]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-390cd866b09sm6275665f8f.19.2025.02.26.08.47.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Feb 2025 08:47:55 -0800 (PST) Date: Wed, 26 Feb 2025 17:47:53 +0100 (CET) From: Sebastian Ott To: Oliver Upton cc: Marc Zyngier , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Shameer Kolothum , Cornelia Huck , Eric Auger , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 0/4] KVM: arm64: writable MIDR/REVIDR In-Reply-To: Message-ID: References: <20250218163443.32836-1-sebott@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Hi Oliver, On Mon, 24 Feb 2025, Oliver Upton wrote: > On Tue, Feb 18, 2025 at 05:34:39PM +0100, Sebastian Ott wrote: >> Based on prior discussion [1] this series allows VMMs to change >> MIDR/REVIDR to enable migration between machines that differ in >> these registers. Since these are used for errata handling the >> errata management series [2] is a prerequisite for this one. >> >> changes for V3: >> * handle VPIDR_EL2 as part of vcpu ctxt - thanks Oliver! > > Thanks for respinning. While your changes are looking good, as I got > ready to apply this series I wound up peeling the onion a bit further > and have a few more concerns: > > - Current KVM allows guests to read SMIDR_EL1 despite the fact that we > do not support SME (this is part of TID1 traps) > > - The "invariant" values that KVM presents to userspace originate from > the boot CPU, not the CPU that resets the ID registers for a VM > > - A VMM that wants to present big-little can do so on current KVM by > affining vCPUs, but cannot with this series > > All of this is to say, I think your series is going to collide with > the pre-existing pile of crap we have. I'm going to pick up these > changes and rework them so we can send a fix for #1 to stable trees and > (hopefully) avoid breaking the old "invariant" behavior. > > I'll post what I have as soon as I test it, hopefully we can get this > shaped up for 6.15. Sry, for the additional work I've caused. I gave what you have in next a spin and it looks good so far. Thank you very much! Sebastian