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=-2.2 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 989D4C43603 for ; Wed, 18 Dec 2019 16:02:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 73CD72146E for ; Wed, 18 Dec 2019 16:02:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727226AbfLRQCa (ORCPT ); Wed, 18 Dec 2019 11:02:30 -0500 Received: from mga02.intel.com ([134.134.136.20]:30328 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727021AbfLRQCa (ORCPT ); Wed, 18 Dec 2019 11:02:30 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 Dec 2019 08:02:28 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,330,1571727600"; d="scan'208";a="217895963" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga006.jf.intel.com with ESMTP; 18 Dec 2019 08:02:28 -0800 Date: Wed, 18 Dec 2019 08:02:28 -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: <20191218160228.GB25201@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> <20191218003455.GP11771@linux.intel.com> <20191218135513.GB7926@local-michael-cet-test> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191218135513.GB7926@local-michael-cet-test> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 18, 2019 at 09:55:13PM +0800, Yang Weijiang wrote: > On Tue, Dec 17, 2019 at 04:34:55PM -0800, Sean Christopherson wrote: > > 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. > > > Thanks, it makes sense to me. Given current implementation, how about > removing above check and adding it in CET CPUID > enumeration for L2 so that no CET msrs passed through to L2 when > is_guest_mode() is true? But you still need to update L1's MSR bitmaps. That can obviously be done all at once, but it's annoying and IMO unnecessarily complex. > > > > 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. > > This sounds like something deserving an individual patch after get > agreement in community. I'll put it aside right now. Normally I would agree, but I think in this case it would significantly reduce the complexity and implementation cost of CET support. I'll send a patch to kickstart the conversation, it's a tiny change in terms of code.