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 4DD2D2E36F1; Sat, 9 Aug 2025 20:21:42 +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=1754770902; cv=none; b=J12mGiVCQ873t4x/K//4UoYKxYyeLZafvXsSJz+5ok+1Ti+jPFqYcwX7arOgtiV4dD+NAvM+Zx0eIkMg4MmQU/PfKCCZn6i0oL1kUMn6BeETG5M8uTGhU3b2FcmAAkdY3KEOU4X9AUbXA0sneKlx2YneBmT8WY+mRQVyOO7WoJQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754770902; c=relaxed/simple; bh=sEv9PYmMWBEnq4cHeF3/88QlEU0nUxNppYfuZI0MI4w=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=B/PT6kYlmIjseW45qGmAwwFNuK6j5hTa63eZRK6fPZDLbS3St3dEZqex7D78snDC67+rIgXAZZ32+JwM4mLZa+gXelKg9ipXnD1Sr6qogk8I08ZdpKNmmVB7h4UOLnrM/NDgeq7AlB/ukko7cDfaojwpgJ+RZuW7Un2LSNHp1zo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=t0vtXvBi; 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="t0vtXvBi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 13CC7C4CEE7; Sat, 9 Aug 2025 20:21:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1754770902; bh=sEv9PYmMWBEnq4cHeF3/88QlEU0nUxNppYfuZI0MI4w=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=t0vtXvBiTdiyGeBfS+qz+5/zNJjDQbJrp68NxASz/zeYJNbHNTDX+AUP4R9dUUACP +AHjUjtdez1AsSOWDZ0HotGytUVcSoVSqCQZof9DT7oBrwwarGrhH+RRz0J9Bq1pkU ZgEhjGm8pI+qXxbbtNeJEddC0QpWO7Ic8ud9ykNewNe1OgnD7YHECEW1uGKF4wxHp4 T1K1msqGvHJ1qubOHaSFcFEtljt3dMd7xOE3Yk5f2BtxYykzVtZcn4WIvMQfQIZez2 DgdNXoXtJf4IvZ8/lJsxTYiF2M9LCZN4+fChU5v/1J3e4mEcDvFuKXtL4MZdw6MyUT qYH4qeVWFn89Q== Received: from sofa.misterjones.org ([185.219.108.64] helo=lobster-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1ukq4R-005hzT-Tt; Sat, 09 Aug 2025 21:21:40 +0100 Date: Sat, 09 Aug 2025 21:21:39 +0100 Message-ID: <8734a0tfe4.wl-maz@kernel.org> From: Marc Zyngier To: Oliver Upton Cc: Joey Gouly , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, Suzuki K Poulose , Zenghui Yu , Will Deacon , Catalin Marinas , Cornelia Huck Subject: Re: [PATCH v2 4/5] KVM: arm64: Expose FEAT_RASv1p1 in a canonical manner In-Reply-To: References: <20250806165615.1513164-1-maz@kernel.org> <20250806165615.1513164-5-maz@kernel.org> <20250807125531.GB2351327@e124191.cambridge.arm.com> 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: kvm@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=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: oliver.upton@linux.dev, joey.gouly@arm.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, suzuki.poulose@arm.com, yuzenghui@huawei.com, will@kernel.org, catalin.marinas@arm.com, cohuck@redhat.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Fri, 08 Aug 2025 23:48:32 +0100, Oliver Upton wrote: > > On Thu, Aug 07, 2025 at 01:55:31PM +0100, Joey Gouly wrote: > > On Wed, Aug 06, 2025 at 05:56:14PM +0100, Marc Zyngier wrote: > > > If we have RASv1p1 on the host, advertise it to the guest in the > > > "canonical way", by setting ID_AA64PFR0_EL1 to V1P1, rather than > > > the convoluted RAS+RAS_frac method. > > > > > > Note that this also advertises FEAT_DoubleFault, which doesn't > > > affect the guest at all, as only EL3 is concerned by this. > > > > > > Signed-off-by: Marc Zyngier > > > --- > > > arch/arm64/kvm/sys_regs.c | 12 ++++++++++++ > > > 1 file changed, 12 insertions(+) > > > > > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > > > index 1b4114790024e..66e5a733e9628 100644 > > > --- a/arch/arm64/kvm/sys_regs.c > > > +++ b/arch/arm64/kvm/sys_regs.c > > > @@ -1800,6 +1800,18 @@ static u64 sanitise_id_aa64pfr0_el1(const struct kvm_vcpu *vcpu, u64 val) > > > if (!vcpu_has_sve(vcpu)) > > > val &= ~ID_AA64PFR0_EL1_SVE_MASK; > > > > > > + /* > > > + * Describe RASv1p1 in a canonical way -- ID_AA64PFR1_EL1.RAS_frac > > > + * is cleared separately. Note that by advertising RASv1p1 here, we > > > > Where is it cleared? __kvm_read_sanitised_id_reg() is where I would have > > expected to see it: > > Actually, I'm a bit worried this change doesn't give us very much value > since Marc already does the exhaustive RASv1p1 check in the sysreg > emulation. > > There's potential for breakage when migrating VMs between new/old kernels > on systems w/ FEAT_RASv1p1 && !FEAT_DoubleFault. > > Marc, WDYT about dropping this patch and instead opening up RAS_frac to > writes? That's indeed probably best. But the question I can't manage to answer right now is how we migrate RASv1p1 between the two versions? It means cross-idreg dependencies, ordering and all that, and I'm a bit reluctant to do so. Thoughts? M. -- Jazz isn't dead. It just smells funny.