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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 16968C43603 for ; Wed, 11 Dec 2019 02:26:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E71FA2073B for ; Wed, 11 Dec 2019 02:26:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727653AbfLKC0D (ORCPT ); Tue, 10 Dec 2019 21:26:03 -0500 Received: from mga01.intel.com ([192.55.52.88]:15739 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727230AbfLKC0C (ORCPT ); Tue, 10 Dec 2019 21:26:02 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 10 Dec 2019 18:26:02 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,301,1571727600"; d="scan'208";a="387778864" Received: from unknown (HELO localhost) ([10.239.159.128]) by orsmga005.jf.intel.com with ESMTP; 10 Dec 2019 18:25:59 -0800 Date: Wed, 11 Dec 2019 10:27:22 +0800 From: Yang Weijiang To: Sean Christopherson Cc: Yang Weijiang , 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: <20191211022722.GA13190@local-michael-cet-test> References: <20191101085222.27997-1-weijiang.yang@intel.com> <20191101085222.27997-4-weijiang.yang@intel.com> <20191210211821.GL15758@linux.intel.com> <20191211013207.GA12845@local-michael-cet-test> <20191211015052.GF23765@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191211015052.GF23765@linux.intel.com> User-Agent: Mutt/1.11.3 (2019-02-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 10, 2019 at 05:50:52PM -0800, Sean Christopherson wrote: > On Wed, Dec 11, 2019 at 09:32:07AM +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. > > > > > > > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > > > > index dd387a785c1e..4166c4fcad1e 100644 > > > > --- a/arch/x86/kvm/cpuid.c > > > > +++ b/arch/x86/kvm/cpuid.c > > > > @@ -371,13 +371,13 @@ static inline void do_cpuid_7_mask(struct kvm_cpuid_entry2 *entry, int index) > > > > F(AVX512VBMI) | F(LA57) | F(PKU) | 0 /*OSPKE*/ | > > > > F(AVX512_VPOPCNTDQ) | F(UMIP) | F(AVX512_VBMI2) | F(GFNI) | > > > > F(VAES) | F(VPCLMULQDQ) | F(AVX512_VNNI) | F(AVX512_BITALG) | > > > > - F(CLDEMOTE) | F(MOVDIRI) | F(MOVDIR64B); > > > > + F(CLDEMOTE) | F(MOVDIRI) | F(MOVDIR64B) | F(SHSTK); > > > > > > > > /* cpuid 7.0.edx*/ > > > > const u32 kvm_cpuid_7_0_edx_x86_features = > > > > F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) | > > > > F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(INTEL_STIBP) | > > > > - F(MD_CLEAR); > > > > + F(MD_CLEAR) | F(IBT); > > > > > > Advertising CET to userspace/guest needs to be done at the end of the > > > series, or at least after CR4.CET is no longer reserved, e.g. KVM_SET_SREGS > > > will fail and the guest will get a #GP when trying to set CR4.CET. > > > > > > I'm pretty sure I've said this at least twice in previous versions of > > > this series... > > > > Thanks Sean for picking these up! > > The reason is, starting from this patch, I'm using guest_cpuid_has(CET) > > to check the availability of guest CET CPUID, so logically I would like to let > > the readers understand CET related CPUID word is > > defined as above. But no problem, I can move these definitions to a > > latter patch as the patchset only meaningful as a whole. > > Adding usage of guest_cpuid_has(CET) without advertising CET is perfectly > ok from a functionality perspective. Having a user without a consumer > isn't ideal, but it's better than having one gigantic patch. > > The problem with advertising CET when it's not fully supported is that it > will break bisection, e.g. trying to boot a CET-enabled guest would get a > #GP during boot and likely crash. Whether or not a series is useful when > taken as a whole is orthogonal to the integrity of each invidiual patch. Oh, I omitted case likes bisection, you're right, I'll change it, thanks a lot!