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 B30001B3B2B; Wed, 21 Aug 2024 11:16:27 +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=1724238987; cv=none; b=GTtMPPhmuaRt72168StGbs+G+frX9hSt+BDNO8muJlyuOW+8LSjIg4cChw9znYfNOdO62Z+IdEr/A9BIUpcmcdA/YXM/w8a19BVeQkBfQH0/klNG5Gbx5mmWiWxMbhXQNPsgyJNgV5qpe3WZQ1p5IonLkaD9XMV9nAXPL+bTG60= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724238987; c=relaxed/simple; bh=PQJeXUClWIAPxChh0edfyISaZ9J1rH+OUORmO3eT5qE=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=e7wKQ+0qOuVLLRJhdsHuLpvB38JyfFKxIBAxGyR54BjARrfmcRtMuNUcJWehKlKPOALHsoC39ARuTimLVpJcqt3d8EK8vj3hpkQzhBE8ciXOkP2Os4AAu3R2GUDXrDWjKFSBCJBRslvtsG38Xkvd38bEEAn39TH47joI24AchrE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FJhxJt02; 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="FJhxJt02" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 450FDC32782; Wed, 21 Aug 2024 11:16:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1724238987; bh=PQJeXUClWIAPxChh0edfyISaZ9J1rH+OUORmO3eT5qE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=FJhxJt02rS7eOjXO6WMjIA2afl2W3RPa2hQxNRh9ASYDKoNVMcShIV6R5cRGkt3A7 UC+EZUNOiBhjPQFxvUuAaJUanS14akEEfAlOXhDWA/shohcACzaxojrFiAHXnPMDJL bkhyvi4Bd3xV4T/Kw4nhtKxxIVyLT0/4tzwPh9e7GzFGGuWU3EWuc/42vdA4CYUn+E KAjolLBZ/L5444f74z1Kz4fcqUUlF6VcbGu5+Ma9jVjgG6TvHKsVkRvbo4Kq/CVo+H H37h/LYuQw/D5WiNt5p5Wxuk44T6//AYWWhsGqIqxT7P3qTrdt86gizHulSF9Jpkiu q/9SLMnEV+eag== 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 4.95) (envelope-from ) id 1sgjKD-005Yj5-1a; Wed, 21 Aug 2024 12:16:25 +0100 Date: Wed, 21 Aug 2024 12:16:24 +0100 Message-ID: <86h6bexh13.wl-maz@kernel.org> From: Marc Zyngier To: Oliver Upton Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, James Morse , Suzuki K Poulose , Zenghui Yu , Alexander Potapenko Subject: Re: [PATCH 06/12] KVM: arm64: Zero ID_AA64PFR0_EL1.GIC when no GICv3 is presented to the guest In-Reply-To: References: <20240820100349.3544850-1-maz@kernel.org> <20240820100349.3544850-7-maz@kernel.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/29.4 (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, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, glider@google.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Wed, 21 Aug 2024 00:50:18 +0100, Oliver Upton wrote: > > On Tue, Aug 20, 2024 at 11:03:43AM +0100, Marc Zyngier wrote: > > In order to be consistent, we shouldn't advertise a GICv3 when none > > is actually usable by the guest. > > > > Wipe the feature when these conditions apply, and allow the field > > to be written from userspace. > > > > Signed-off-by: Marc Zyngier > > --- > > arch/arm64/kvm/sys_regs.c | 6 +++++- > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > > index bc2d54da3827..7d00d7e359e1 100644 > > --- a/arch/arm64/kvm/sys_regs.c > > +++ b/arch/arm64/kvm/sys_regs.c > > @@ -2365,7 +2365,6 @@ static const struct sys_reg_desc sys_reg_descs[] = { > > ID_AA64PFR0_EL1_MPAM | > > ID_AA64PFR0_EL1_SVE | > > ID_AA64PFR0_EL1_RAS | > > - ID_AA64PFR0_EL1_GIC | > > ID_AA64PFR0_EL1_AdvSIMD | > > ID_AA64PFR0_EL1_FP), }, > > ID_SANITISED(ID_AA64PFR1_EL1), > > @@ -4634,6 +4633,11 @@ int kvm_finalize_sys_regs(struct kvm_vcpu *vcpu) > > > > guard(mutex)(&kvm->arch.config_lock); > > > > + if (!kvm_has_gicv3(kvm)) { > > + kvm->arch.id_regs[IDREG_IDX(SYS_ID_AA64PFR0_EL1)] &= ~ID_AA64PFR0_EL1_GIC_MASK; > > + kvm->arch.id_regs[IDREG_IDX(SYS_ID_PFR1_EL1)] &= ~ID_PFR1_EL1_GIC_MASK; > > + } > > + > > Hmm, should we use the ID register field as the source of truth for > kvm_has_gicv3() at this point? > > I think what you have in patch #1 makes good sense for a stable > backport. Using the ID register from this point forward would make the > behavior consistent for a stupid userspace instantiated GICv3 for the VM > but clobbered it from the ID register. > > AFAICT all other usage of kvm_has_gicv3() happens after > kvm_finalize_sys_regs(), so it should take this last-minute fixup into > account. Right, so changing the definition of kvm_has_gicv3() in this patch, and using the "old" definition here only. Yup, this seems like a reasonable thing to do. Thanks, M. -- Without deviation from the norm, progress is not possible.