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Mon, 11 May 2026 07:56:26 +0000 Date: Mon, 11 May 2026 08:56:25 +0100 Message-ID: <86ik8uxtue.wl-maz@kernel.org> From: Marc Zyngier To: David Woodhouse Cc: Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Paolo Bonzini , Shuah Khan , Raghavendra Rao Ananta , Eric Auger , Kees Cook , Arnd Bergmann , Nathan Chancellor , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: (subset) [PATCH 1/3] KVM: arm64: vgic: Fix IIDR revision field extracted from wrong value In-Reply-To: References: <20260407210949.2076251-1-dwmw2@infradead.org> <20260407210949.2076251-2-dwmw2@infradead.org> <177702878141.537738.13460155220731277452.b4-ty@kernel.org> <106addd3f78918a9a584c43c181a9609aef1ceca.camel@infradead.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/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: dwmw2@infradead.org, oupton@kernel.org, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, pbonzini@redhat.com, shuah@kernel.org, rananta@google.com, eric.auger@redhat.com, kees@kernel.org, arnd@arndb.de, nathan@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@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-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 Sun, 10 May 2026 22:28:50 +0100, David Woodhouse wrote: >=20 > [1 ] > On Fri, 2026-04-24 at 13:24 +0100, David Woodhouse wrote: > > On Fri, 2026-04-24 at 12:07 +0100, Marc Zyngier wrote: > > > On Tue, 07 Apr 2026 21:27:02 +0100, David Woodhouse wrote: > > > > The uaccess write handlers for GICD_IIDR in both GICv2 and GICv3 > > > > extract the revision field from 'reg' (the current IIDR value read = back > > > > from the emulated distributor) instead of 'val' (the value userspac= e is > > > > trying to write). This means userspace can never actually change the > > > > implementation revision =E2=80=94 the extracted value is always the= current one. > > > >=20 > > > > Fix the FIELD_GET to use 'val' so that userspace can select a diffe= rent > > > > revision for migration compatibility. > > > >=20 > > > > [...] > > >=20 > > > Applied to fixes, thanks! > > >=20 > > > [1/3] KVM: arm64: vgic: Fix IIDR revision field extracted from wrong = value > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 commit: a0e6ae45af17e8b27958830595799c= 702ffbab8d > >=20 > > There was a v2 of this series which also cleaned up the weird > > inconsistency of the IIDR value with the actual behaviour, and which > > fixed the fact that it's currently not possible to maintain guest > > compatibility when upgrading from a pre-d53c2c29ae0d kernel to a new > > one =E2=80=94 despite the fact that that kind of compatibility is *prec= isely* > > what the revision field in the IIDR is designed for. > >=20 > > https://lore.kernel.org/all/20260408113256.2095505-1-dwmw2@infradead.or= g/ >=20 > Is there a reason the rest of these fixes didn't make 7.1? I already explained why these changes are neither necessary (a guest that used to run still runs) nor desirable (reintroducing bugs we have fixed is a bad idea). I have therefore only taken the fix for the bug affecting userspace, as that was definitely something worth fixing. M. --=20 Without deviation from the norm, progress is not possible.