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 7C069C433F5 for ; Fri, 21 Jan 2022 13:30:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1380772AbiAUNaZ (ORCPT ); Fri, 21 Jan 2022 08:30:25 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:58109 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1380720AbiAUNaJ (ORCPT ); Fri, 21 Jan 2022 08:30:09 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1642771753; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XcWu6s4pN5jlEkVju4/UBrdbowSjhtmAIaPpgML9RtY=; b=ZnC5+vWiGV/Kw8yLG3xYgG4xIgcVl7ZADpwPkjiCxt8AC5EacPWHMxNJd61tB69Oe652ph QsSz+0N8eQ029QJ83H1+KSgLjistYECI2yIYD5tYloc7ygll2ZHhBtP/bmKTeH/Le3qKgB I4pAI7220ZWFRaDpIBvjukIYusEToWI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-325-HZhNq7LqNTe5hEetPfEeuQ-1; Fri, 21 Jan 2022 08:29:05 -0500 X-MC-Unique: HZhNq7LqNTe5hEetPfEeuQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3FC6084DA41; Fri, 21 Jan 2022 13:29:04 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.40.195.38]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1E8457E228; Fri, 21 Jan 2022 13:29:01 +0000 (UTC) From: Vitaly Kuznetsov To: kvm@vger.kernel.org, Paolo Bonzini Cc: Sean Christopherson , Wanpeng Li , Jim Mattson , Igor Mammedov , linux-kernel@vger.kernel.org Subject: [PATCH v4 3/5] KVM: x86: Partially allow KVM_SET_CPUID{,2} after KVM_RUN Date: Fri, 21 Jan 2022 14:28:50 +0100 Message-Id: <20220121132852.2482355-4-vkuznets@redhat.com> In-Reply-To: <20220121132852.2482355-1-vkuznets@redhat.com> References: <20220121132852.2482355-1-vkuznets@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- arch/x86/kvm/cpuid.c | 31 +++++++++++++++++++++++++++++++ arch/x86/kvm/x86.c | 19 ------------------- 2 files changed, 31 insertions(+), 19 deletions(-) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 7c48daee6670..96556bf494fc 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -119,6 +119,19 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu, return fpu_enable_guest_xfd_features(&vcpu->arch.guest_fpu, xfeatures); } +/* 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) +{ + if (nent != vcpu->arch.cpuid_nent) + return -EINVAL; + + if (memcmp(e2, vcpu->arch.cpuid_entries, nent * sizeof(*e2))) + return -EINVAL; + + return 0; +} + static void kvm_update_kvm_cpuid_base(struct kvm_vcpu *vcpu) { u32 function; @@ -325,6 +338,24 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2, __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. To avoid potential hard to debug + * problems, forbid changing CPUID data after successfully entering the + * guest. Banning KVM_SET_CPUID{,2} altogether is incompatible with + * certain VMMs (e.g. QEMU) which reuse vCPU fds for CPU hotplug as + * KVM_SET_CPUID{,2} call (with the same CPUID data) may be issued again + * upon hotplug. + * Note, there are other problematic scenarios which are currently not + * being handled, e.g. supplying different CPUID data for different + * vCPUs also won't be handled correctly by KVM MMU. + */ + if (vcpu->arch.last_vmentry_cpu != -1) + return kvm_cpuid_check_equal(vcpu, e2, nent); + r = kvm_check_cpuid(vcpu, e2, nent); if (r) return r; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 76b4803dd3bd..ff1416010728 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5230,17 +5230,6 @@ long kvm_arch_vcpu_ioctl(struct file *filp, 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; @@ -5251,14 +5240,6 @@ long kvm_arch_vcpu_ioctl(struct file *filp, 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; -- 2.34.1