From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 358EEC433EF for ; Tue, 8 Feb 2022 14:41:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351359AbiBHOll (ORCPT ); Tue, 8 Feb 2022 09:41:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41638 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351489AbiBHOlk (ORCPT ); Tue, 8 Feb 2022 09:41:40 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B3038C03FEDD for ; Tue, 8 Feb 2022 06:41:37 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 4EE046125B for ; Tue, 8 Feb 2022 14:41:37 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B272DC004E1; Tue, 8 Feb 2022 14:41:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1644331296; bh=+h0u0N03bHsQ0A+M4QKwabtt6GrHdxbl/EmS9Cvmiiw=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=pSTu4q6qit/DGC0R5ErSLYtEqOqdRpGaJTw41uvyS7SD4JGpxTQgpF+nn4U1duv+A Um1mMi8eUNZOKJicLfzyO1zSz1d1iAXclOtZExKcQ8xSReuUlmxJI7/yVbW77RMozl ewg35zk7UQqTpg1Y1QeW7ejAz2IzMWv3AebkZ5R0fawkFZG6amvxZJW+enjBk7bbyD U4o4ga7tjGGQ7r4fHJbs53zNlsUPuimeziD47g19Up8bBSvGtDLOzxvifuWY5VxIvR UX6FJht8lUIeARDQLAvBvhmheVel7NSc3Wm0oQ6j4yAwolJqY+rni544/AMyP7y8Hq EPXhxm2j9lExQ== Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1nHRgT-006HlP-3v; Tue, 08 Feb 2022 14:41:34 +0000 Date: Tue, 08 Feb 2022 14:41:32 +0000 Message-ID: <87a6f15skj.wl-maz@kernel.org> From: Marc Zyngier To: Reiji Watanabe Cc: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, James Morse , Alexandru Elisei , Suzuki K Poulose , Paolo Bonzini , Will Deacon , Peter Shier , Ricardo Koller , Oliver Upton , Jing Zhang , Raghavendra Rao Anata Subject: Re: [PATCH v2 1/2] KVM: arm64: mixed-width check should be skipped for uninitialized vCPUs In-Reply-To: <20220118041923.3384602-1-reijiw@google.com> References: <20220118041923.3384602-1-reijiw@google.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/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) 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: reijiw@google.com, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, pbonzini@redhat.com, will@kernel.org, pshier@google.com, ricarkol@google.com, oupton@google.com, jingzhangos@google.com, rananta@google.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, 18 Jan 2022 04:19:22 +0000, Reiji Watanabe wrote: > > KVM allows userspace to configure either all 32bit or 64bit vCPUs > for a guest. At vCPU reset, vcpu_allowed_register_width() checks > if the vcpu's register width is consistent with all other vCPUs'. > Since the checking is done even against vCPUs that are not initialized > (KVM_ARM_VCPU_INIT has not been done) yet, the uninitialized vCPUs > are erroneously treated as 64bit vCPU, which causes the function to > incorrectly detect a mixed-width VM. > > Introduce a new flag (el1_reg_width) in kvm_arch to indicates that > the guest needs to be configured with all 32bit or 64bit vCPUs, > and initialize it at the first KVM_ARM_VCPU_INIT for the guest. > Check vcpu's register width against the flag at the vcpu's > KVM_ARM_VCPU_INIT (instead of against other vCPUs' register width). > > Fixes: 66e94d5cafd4 ("KVM: arm64: Prevent mixed-width VM creation") > Signed-off-by: Reiji Watanabe > --- > arch/arm64/include/asm/kvm_host.h | 13 +++++++++++++ > arch/arm64/kvm/arm.c | 30 ++++++++++++++++++++++++++++++ > arch/arm64/kvm/reset.c | 8 -------- > 3 files changed, 43 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index 2a5f7f38006f..c02b7caf2c82 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -102,6 +102,12 @@ struct kvm_s2_mmu { > struct kvm_arch_memory_slot { > }; > > +enum kvm_el1_reg_width { > + EL1_WIDTH_UNINITIALIZED = 0, > + EL1_32BIT, > + EL1_64BIT, > +}; > + > struct kvm_arch { > struct kvm_s2_mmu mmu; > > @@ -137,6 +143,13 @@ struct kvm_arch { > > /* Memory Tagging Extension enabled for the guest */ > bool mte_enabled; > + > + /* > + * EL1 register width for the guest. > + * This is set at the first KVM_ARM_VCPU_INIT for the guest based > + * on whether the vcpu has KVM_ARM_VCPU_EL1_32BIT or not. > + */ > + enum kvm_el1_reg_width el1_reg_width; I really don't like that we need to keep track of yet another bit of state on top of the existing one. Duplicating state is a source of bugs, because you always end up checking the wrong one at the wrong time (and I have scars to prove it). > }; > > struct kvm_vcpu_fault_info { > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index e4727dc771bf..54ae8bf9d187 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -1058,6 +1058,32 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_level, > return -EINVAL; > } > > +/* > + * A guest can have either all 32bit or 64bit vcpus only. That's not strictly true. All we are enforcing is that EL1 is either 32 or 64bit. > + * Either one the guest has is indicated in kvm->arch.el1_reg_width. > + * Check if the vcpu's register width is consistent with > + * kvm->arch.el1_reg_width. If kvm->arch.el1_reg_width is not set yet, > + * set it based on the vcpu's KVM_ARM_VCPU_EL1_32BIT configuration. > + */ > +static int kvm_register_width_check_or_init(struct kvm_vcpu *vcpu) > +{ > + bool is32bit; > + bool allowed = true; > + struct kvm *kvm = vcpu->kvm; > + > + is32bit = vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT); > + > + mutex_lock(&kvm->lock); > + > + if (kvm->arch.el1_reg_width == EL1_WIDTH_UNINITIALIZED) > + kvm->arch.el1_reg_width = is32bit ? EL1_32BIT : EL1_64BIT; > + else > + allowed = (is32bit == (kvm->arch.el1_reg_width == EL1_32BIT)); > + > + mutex_unlock(&kvm->lock); > + return allowed ? 0 : -EINVAL; > +} > + > static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu, > const struct kvm_vcpu_init *init) > { > @@ -1097,6 +1123,10 @@ static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu, > > /* Now we know what it is, we can reset it. */ > ret = kvm_reset_vcpu(vcpu); > + > + if (!ret) > + ret = kvm_register_width_check_or_init(vcpu); > + > if (ret) { > vcpu->arch.target = -1; > bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES); > diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c > index 426bd7fbc3fd..dbf2939a6a96 100644 > --- a/arch/arm64/kvm/reset.c > +++ b/arch/arm64/kvm/reset.c > @@ -168,9 +168,7 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu) > > static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu) > { > - struct kvm_vcpu *tmp; > bool is32bit; > - int i; > > is32bit = vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT); > if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) && is32bit) > @@ -180,12 +178,6 @@ static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu) > if (kvm_has_mte(vcpu->kvm) && is32bit) > return false; > > - /* Check that the vcpus are either all 32bit or all 64bit */ > - kvm_for_each_vcpu(i, tmp, vcpu->kvm) { > - if (vcpu_has_feature(tmp, KVM_ARM_VCPU_EL1_32BIT) != is32bit) > - return false; > - } > - In [1], I suggested another approach that didn't require extra state, and moved the existing checks under the kvm lock. What was wrong with that approach? Thanks, M. [1] https://lore.kernel.org/r/875yqqtn5q.wl-maz@kernel.org -- Without deviation from the norm, progress is not possible.