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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT 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 1681EC43381 for ; Mon, 4 Mar 2019 18:28:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DCAAC206DD for ; Mon, 4 Mar 2019 18:28:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727204AbfCDS2j (ORCPT ); Mon, 4 Mar 2019 13:28:39 -0500 Received: from mga09.intel.com ([134.134.136.24]:3509 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726063AbfCDS2j (ORCPT ); Mon, 4 Mar 2019 13:28:39 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 04 Mar 2019 10:28:37 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,440,1544515200"; d="scan'208";a="325323690" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.181]) by fmsmga005.fm.intel.com with ESMTP; 04 Mar 2019 10:28:36 -0800 Date: Mon, 4 Mar 2019 10:28:36 -0800 From: Sean Christopherson To: Yang Weijiang Cc: pbonzini@redhat.com, rkrcmar@redhat.com, jmattson@google.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, mst@redhat.com, yu-cheng.yu@intel.com, Zhang Yi Z Subject: Re: [PATCH v3 3/8] KVM:CPUID: Add CPUID support for Guest CET Message-ID: <20190304182836.GB17120@linux.intel.com> References: <20190225132716.6982-1-weijiang.yang@intel.com> <20190225132716.6982-4-weijiang.yang@intel.com> <20190228155939.GD6166@linux.intel.com> <20190228082831.GB12006@local-michael-cet-test.sh.intel.com> <20190301145323.GB22584@linux.intel.com> <20190303093645.GB31538@local-michael-cet-test.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190303093645.GB31538@local-michael-cet-test.sh.intel.com> 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 Sun, Mar 03, 2019 at 05:36:45PM +0800, Yang Weijiang wrote: > On Fri, Mar 01, 2019 at 06:53:23AM -0800, Sean Christopherson wrote: > > On Thu, Feb 28, 2019 at 04:28:32PM +0800, Yang Weijiang wrote: > > > On Thu, Feb 28, 2019 at 07:59:40AM -0800, Sean Christopherson wrote: > > > > On Mon, Feb 25, 2019 at 09:27:11PM +0800, Yang Weijiang wrote: > > > > > Guest CET SHSTK and IBT capability are reported via > > > > > CPUID.(EAX=7, ECX=0):ECX[bit 7] and EDX[bit 20] respectively. > > > > > Guest user mode and supervisor mode xsaves component size > > > > > is reported via CPUID.(EAX=0xD, ECX=1):ECX[bit 11] and ECX[bit 12] > > > > > respectively. > > > > > > > > > > Signed-off-by: Zhang Yi Z > > > > > Signed-off-by: Yang Weijiang > > > > > --- > > > > > arch/x86/kvm/cpuid.c | 60 +++++++++++++++++++++++++++++++++----------- > > > > > arch/x86/kvm/x86.h | 4 +++ > > > > > 2 files changed, 50 insertions(+), 14 deletions(-) > > > > > > > > > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > > > > > index cb1aece25b17..5e05756cc6db 100644 > > > > > --- a/arch/x86/kvm/cpuid.c > > > > > +++ b/arch/x86/kvm/cpuid.c > > > > > @@ -65,6 +65,16 @@ u64 kvm_supported_xcr0(void) > > > > > return xcr0; > > > > > } > > > > > > > > > > +u64 kvm_supported_xss(void) > > > > > +{ > > > > > + u64 xss; > > > > > + > > > > > + rdmsrl(MSR_IA32_XSS, xss); > > > > > + xss &= KVM_SUPPORTED_XSS; > > > > > + return xss; > > > > > +} > > > > > +EXPORT_SYMBOL(kvm_supported_xss); > > > > > + > > > > > #define F(x) bit(X86_FEATURE_##x) > > > > > > > > > > /* For scattered features from cpufeatures.h; we currently expose none */ > > > > > @@ -323,6 +333,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, > > > > > u32 index, int *nent, int maxnent) > > > > > { > > > > > int r; > > > > > + u32 eax, ebx, ecx, edx; > > > > > unsigned f_nx = is_efer_nx() ? F(NX) : 0; > > > > > #ifdef CONFIG_X86_64 > > > > > unsigned f_gbpages = (kvm_x86_ops->get_lpage_level() == PT_PDPE_LEVEL) > > > > > @@ -503,6 +514,20 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, > > > > > * if the host doesn't support it. > > > > > */ > > > > > entry->edx |= F(ARCH_CAPABILITIES); > > > > > + > > > > > + /* > > > > > + * Guest OS CET enabling is designed independent to > > > > > + * host enabling, it only has dependency on Host HW > > > > > + * capability, if it has, report CET support to > > > > > + * Guest. > > > > > + */ > > > > > + cpuid_count(7, 0, &eax, &ebx, &ecx, &edx); > > > > > + if (ecx & F(SHSTK)) > > > > > + entry->ecx |= F(SHSTK); > > > > > + > > > > > + if (edx & F(IBT)) > > > > > + entry->edx |= F(IBT); > > > > > > > > There's no need to manually add these flags. They will be automatically > > > > kept if supported in hardware because your previous patch, 02/08, added > > > > them to the mask of features that can be exposed to the guest, > > > > i.e. set them in kvm_cpuid_7_0_e{c,d}x_x86_features. > > > > > > > I shared the same thought as you before, but after I took a closer look at the > > > kernel code, actually, when host CET feature is disabled by user via > > > cmdline options(no_cet_shstk and no_cet_ibt), it'll mask out CET feature bits in > > > boot_cpu_data.x86_capbility[] array, and cpuid_mask() will make the bits > > > in previous definition lost, so these lines actually add them back when > > > host CET is disabled. > > > > 'entry' is filled by do_cpuid_1_ent(), which does cpuid_count(), same as > > your code, i.e. it's not affected by whether or not the host kernel is > > using each feature. > > > I checked CET kernel patch: > #ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER > static __init int setup_disable_shstk(char *s) { > /* require an exact match without trailing characters */ > if (s[0] != '\0') > return 0; > > if (!boot_cpu_has(X86_FEATURE_SHSTK)) > return 1; > > setup_clear_cpu_cap(X86_FEATURE_SHSTK); > pr_info("x86: 'no_cet_shstk' specified, disabling Shadow Stack\n"); > return 1; > } > __setup("no_cet_shstk", setup_disable_shstk); #endif > > setup_disable_shstk()->setup_clear_cpu_cap(X86_FEATURE_SHSTK)->do_clear_cpu_cap(NULL, > feature)->clear_feature(c, feature)->clear_cpu_cap(&boot_cpu_data, feature); > > this path will clear boot_cpu_data.x86_capability[X86_FEATURE_SHSTK] if "no_cet_shstk" is set. > but in cpuid_mask(), it will "AND" the bit with SHSTK bit set > in kvm_cpuid_7_0_ecx_x86_features, so the bit in ecx is cleared, > need to add the bit back according to host cpuid_count(). > the CET kernel patch can be seen in below patch link. Ah, I see. In this case we need to honor boot_cpu_data. The idea is that a feature should not be exposed to the guest, i.e. actually used, if it has been explicitly disabled by the user, e.g. to workaround a hardware or firmware issue. The cases where a feature is exposed to the guest even when disabled in host is when said feature is emulated by KVM in software. > > > > please check CET kernel patch here: > > > https://lkml.org/lkml/2018/11/20/204