From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0B66E3A6B63; Mon, 11 May 2026 07:56:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778486190; cv=none; b=QFeAzoFe2H47xi90PHHBI/6hOqfJj9tHRSoiEmW1rVDFdg9Lun8s7Nq7PUI1PAoEMqGenY40rulEtso/3SNq3Dlh5cm3RkmoD/UodUhB9kNhP01hpzeL1QCuXfaru9a8DZ7v0MX4eI6I1dowBCYnrn8HrOLxQlXnFpUI2B9u1r0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778486190; c=relaxed/simple; bh=QMHKoXETT7g06zajK518cc22bHdzyrX5waNPKMUdKn8=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=joWp3Kgn+1Ebhi2vzPf7NfSlP+gAwMQhJ8tk2VO+PZCBhCgpc9C76w5h+27brhUxz5AV8J724X6R46XXgcyj+lJpz+5/7NbDURlwFx3Oy7KJ5jtPZPMX0mPAQrSV83yTmU8mAjxrDfyZq0HFuTc7IGDLs0SH5HmL6VhPumS3fxo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NLNYc2bi; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NLNYc2bi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9CBB1C2BCB0; Mon, 11 May 2026 07:56:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778486188; bh=QMHKoXETT7g06zajK518cc22bHdzyrX5waNPKMUdKn8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=NLNYc2biY2meoXUGwOxLGT4Q+CZ60AeUK49W7/7n70oto3SwdCsBlASjbdY4Nw25H pKLltqHSz9cDBVU85+8QyYg9JkaRxC8DAX2fndv7IaNZaTJoRbpRBCiO2GKykXOqDQ AjCDbSwYoEQxF/Ei4Fn722yyTnKlmzGqj2OBJx5BcfzH/4h9ULvagnc9uwcUfOFHpW qGQLqSsYHhSscH4m6QoDYtM0YYCkMxG7Vy6kiMALnskBmiO4ViBaJkMX++M/jGfCDM ws5L+JigLECRvmc4q864DgY58BNvvP3cuItLYwHNhp5xGj/otrV2oapRw9AEI6GWYJ 9pIMrs/9cV0CA== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1wMLV4-00000000zbK-1B8r; 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) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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.