From patchwork Mon Jan 24 18:47:02 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 535265 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 634BBC43219 for ; Mon, 24 Jan 2022 21:58:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1454897AbiAXVy7 (ORCPT ); Mon, 24 Jan 2022 16:54:59 -0500 Received: from ams.source.kernel.org ([145.40.68.75]:52676 "EHLO ams.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1573482AbiAXVo6 (ORCPT ); Mon, 24 Jan 2022 16:44:58 -0500 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 ams.source.kernel.org (Postfix) with ESMTPS id 8842FB80CCF; Mon, 24 Jan 2022 21:44:57 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9CBF5C340E4; Mon, 24 Jan 2022 21:44:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1643060696; bh=93huczeIyL5LcJsflgRKmCn63D+6drfz/04KRlXSC0g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=yEJy/fSU0ZwRBJnByBi4HS+eiUHXLIq8Ej3yBk4ORxom3J/FAfo8HVNicVC4bc3NF PX9e3Lvts57LoNTcCtamDwggCazlz1o0qE5859AOjwUSckvYX2+VDMs5otT12+XShe PucH1dnFVjSUOUsMSW31Au5isiWQlRup40lkOi4A= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg Kroah-Hartman , Igor Mammedov , Vitaly Kuznetsov , Paolo Bonzini Subject: [PATCH 5.16 1033/1039] KVM: x86: Partially allow KVM_SET_CPUID{,2} after KVM_RUN Date: Mon, 24 Jan 2022 19:47:02 +0100 Message-Id: <20220124184200.012351266@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220124184125.121143506@linuxfoundation.org> References: <20220124184125.121143506@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Vitaly Kuznetsov commit c6617c61e8fe44b9e9fdfede921f61cac6b5149d upstream. Commit feb627e8d6f6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN") forbade changing CPUID altogether but unfortunately this is not fully compatible with existing VMMs. In particular, QEMU reuses vCPU fds for CPU hotplug after unplug and it calls KVM_SET_CPUID2. Instead of full ban, check whether the supplied CPUID data is equal to what was previously set. Reported-by: Igor Mammedov Fixes: feb627e8d6f6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN") Signed-off-by: Vitaly Kuznetsov Message-Id: <20220117150542.2176196-3-vkuznets@redhat.com> Cc: stable@vger.kernel.org [Do not call kvm_find_cpuid_entry repeatedly. - Paolo] Signed-off-by: Paolo Bonzini Signed-off-by: Vitaly Kuznetsov Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/cpuid.c | 36 ++++++++++++++++++++++++++++++++++++ arch/x86/kvm/x86.c | 19 ------------------- 2 files changed, 36 insertions(+), 19 deletions(-) --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -99,6 +99,28 @@ static int kvm_check_cpuid(struct kvm_cp return 0; } +/* Check whether the supplied CPUID data is equal to what is already set for the vCPU. */ +static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2, + int nent) +{ + struct kvm_cpuid_entry2 *orig; + int i; + + if (nent != vcpu->arch.cpuid_nent) + return -EINVAL; + + for (i = 0; i < nent; i++) { + orig = &vcpu->arch.cpuid_entries[i]; + if (e2[i].function != orig->function || + e2[i].index != orig->index || + e2[i].eax != orig->eax || e2[i].ebx != orig->ebx || + e2[i].ecx != orig->ecx || e2[i].edx != orig->edx) + return -EINVAL; + } + + return 0; +} + static void kvm_update_kvm_cpuid_base(struct kvm_vcpu *vcpu) { u32 function; @@ -293,6 +315,20 @@ static int kvm_set_cpuid(struct kvm_vcpu __kvm_update_cpuid_runtime(vcpu, e2, nent); + /* + * KVM does not correctly handle changing guest CPUID after KVM_RUN, as + * MAXPHYADDR, GBPAGES support, AMD reserved bit behavior, etc.. aren't + * tracked in kvm_mmu_page_role. As a result, KVM may miss guest page + * faults due to reusing SPs/SPTEs. In practice no sane VMM mucks with + * the core vCPU model on the fly. It would've been better to forbid any + * KVM_SET_CPUID{,2} calls after KVM_RUN altogether but unfortunately + * some VMMs (e.g. QEMU) reuse vCPU fds for CPU hotplug/unplug and do + * KVM_SET_CPUID{,2} again. To support this legacy behavior, check + * whether the supplied CPUID data is equal to what's already set. + */ + if (vcpu->arch.last_vmentry_cpu != -1) + return kvm_cpuid_check_equal(vcpu, e2, nent); + r = kvm_check_cpuid(e2, nent); if (r) return r; --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5149,17 +5149,6 @@ long kvm_arch_vcpu_ioctl(struct file *fi struct kvm_cpuid __user *cpuid_arg = argp; struct kvm_cpuid cpuid; - /* - * KVM does not correctly handle changing guest CPUID after KVM_RUN, as - * MAXPHYADDR, GBPAGES support, AMD reserved bit behavior, etc.. aren't - * tracked in kvm_mmu_page_role. As a result, KVM may miss guest page - * faults due to reusing SPs/SPTEs. In practice no sane VMM mucks with - * the core vCPU model on the fly, so fail. - */ - r = -EINVAL; - if (vcpu->arch.last_vmentry_cpu != -1) - goto out; - r = -EFAULT; if (copy_from_user(&cpuid, cpuid_arg, sizeof(cpuid))) goto out; @@ -5170,14 +5159,6 @@ long kvm_arch_vcpu_ioctl(struct file *fi struct kvm_cpuid2 __user *cpuid_arg = argp; struct kvm_cpuid2 cpuid; - /* - * KVM_SET_CPUID{,2} after KVM_RUN is forbidded, see the comment in - * KVM_SET_CPUID case above. - */ - r = -EINVAL; - if (vcpu->arch.last_vmentry_cpu != -1) - goto out; - r = -EFAULT; if (copy_from_user(&cpuid, cpuid_arg, sizeof(cpuid))) goto out;