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From: Oliver Upton To: Sebastian Ott 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 Message-ID: References: <20250218163443.32836-1-sebott@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250226_105629_218335_EDB8E4BC X-CRM114-Status: GOOD ( 26.10 ) 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 Wed, Feb 26, 2025 at 05:47:53PM +0100, Sebastian Ott wrote: > 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! Don't apologize -- it isn't your fault what we had already was a mess! :) Thanks for kicking the tires. Best, Oliver