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 X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D1A33C43603 for ; Wed, 18 Dec 2019 00:34:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AAD1324679 for ; Wed, 18 Dec 2019 00:34:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726402AbfLRAe4 (ORCPT ); Tue, 17 Dec 2019 19:34:56 -0500 Received: from mga09.intel.com ([134.134.136.24]:49459 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725940AbfLRAez (ORCPT ); Tue, 17 Dec 2019 19:34:55 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 17 Dec 2019 16:34:55 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,327,1571727600"; d="scan'208";a="205662246" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga007.jf.intel.com with ESMTP; 17 Dec 2019 16:34:55 -0800 Date: Tue, 17 Dec 2019 16:34:55 -0800 From: Sean Christopherson To: Yang Weijiang Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, jmattson@google.com, yu.c.zhang@linux.intel.com, yu-cheng.yu@intel.com Subject: Re: [PATCH v8 3/7] KVM: VMX: Pass through CET related MSRs Message-ID: <20191218003455.GP11771@linux.intel.com> References: <20191101085222.27997-1-weijiang.yang@intel.com> <20191101085222.27997-4-weijiang.yang@intel.com> <20191210211821.GL15758@linux.intel.com> <20191216021816.GA10764@local-michael-cet-test> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191216021816.GA10764@local-michael-cet-test> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Dec 16, 2019 at 10:18:16AM +0800, Yang Weijiang wrote: > On Tue, Dec 10, 2019 at 01:18:21PM -0800, Sean Christopherson wrote: > > On Fri, Nov 01, 2019 at 04:52:18PM +0800, Yang Weijiang wrote: > > > CET MSRs pass through Guest directly to enhance performance. > > > CET runtime control settings are stored in MSR_IA32_{U,S}_CET, > > > Shadow Stack Pointer(SSP) are stored in MSR_IA32_PL{0,1,2,3}_SSP, > > > SSP table base address is stored in MSR_IA32_INT_SSP_TAB, > > > these MSRs are defined in kernel and re-used here. > > > > > + > > > static void vmx_cpuid_update(struct kvm_vcpu *vcpu) > > > { > > > struct vcpu_vmx *vmx = to_vmx(vcpu); > > > @@ -7025,6 +7087,9 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu) > > > if (boot_cpu_has(X86_FEATURE_INTEL_PT) && > > > guest_cpuid_has(vcpu, X86_FEATURE_INTEL_PT)) > > > update_intel_pt_cfg(vcpu); > > > + > > > + if (!is_guest_mode(vcpu)) > > > + vmx_pass_cet_msrs(vcpu); > > > > Hmm, this looks insufficent, e.g. deliberately toggling CET from on->off > > while in guest mode would put KVM in a weird state as the msr bitmap for > > L1 would still allow L1 to access the CET MSRs. > > > Hi, Sean, > I don't get you, there's guest mode check before access CET msrs, it'll > fail if it's in guest mode. KVM can exit to userspae while L2 is active. If userspace then did a KVM_SET_CPUID2, e.g. instead of KVM_RUN, vmx_cpuid_update() would skip vmx_pass_cet_msrs() and KVM would never update L1's MSR bitmaps. > > Allowing KVM_SET_CPUID{2} while running a nested guest seems bogus, can we > > kill that path entirely with -EINVAL? > > > Do you mean don't expose CET cpuids to L2 guest? I mean completely disallow KVM_SET_CPUID and KVM_SET_CPUID2 if is_guest_mode() is true. My question is mostly directed at Paolo and anyone else that has an opinion on whether we can massage the ABI to retroactively change KVM_SET_CPUID{2} behavior.