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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 D4299C31E40 for ; Mon, 12 Aug 2019 23:02:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B10162070C for ; Mon, 12 Aug 2019 23:02:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726684AbfHLXCF (ORCPT ); Mon, 12 Aug 2019 19:02:05 -0400 Received: from mga03.intel.com ([134.134.136.65]:21131 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726296AbfHLXCE (ORCPT ); Mon, 12 Aug 2019 19:02:04 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Aug 2019 16:02:03 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,379,1559545200"; d="scan'208";a="204889364" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.41]) by fmsmga002.fm.intel.com with ESMTP; 12 Aug 2019 16:02:03 -0700 Date: Mon, 12 Aug 2019 16:02:03 -0700 From: Sean Christopherson To: Yang Weijiang Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, mst@redhat.com, rkrcmar@redhat.com, jmattson@google.com Subject: Re: [PATCH v6 7/8] KVM: x86: Load Guest fpu state when accessing MSRs managed by XSAVES Message-ID: <20190812230203.GC4996@linux.intel.com> References: <20190725031246.8296-1-weijiang.yang@intel.com> <20190725031246.8296-8-weijiang.yang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190725031246.8296-8-weijiang.yang@intel.com> 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 Thu, Jul 25, 2019 at 11:12:45AM +0800, Yang Weijiang wrote: > From: Sean Christopherson > > A handful of CET MSRs are not context switched through "traditional" > methods, e.g. VMCS or manual switching, but rather are passed through > to the guest and are saved and restored by XSAVES/XRSTORS, i.e. the > guest's FPU state. > > Load the guest's FPU state if userspace is accessing MSRs whose values > are managed by XSAVES so that the MSR helper, e.g. vmx_{get,set}_msr(), > can simply do {RD,WR}MSR to access the guest's value. > > Note that guest_cpuid_has() is not queried as host userspace is allowed > to access MSRs that have not been exposed to the guest, e.g. it might do > KVM_SET_MSRS prior to KVM_SET_CPUID2. > > Signed-off-by: Sean Christopherson > Co-developed-by: Yang Weijiang > Signed-off-by: Yang Weijiang > --- > arch/x86/kvm/x86.c | 29 ++++++++++++++++++++++++++++- > 1 file changed, 28 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index fafd81d2c9ea..c657e6a56527 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -102,6 +102,8 @@ static void enter_smm(struct kvm_vcpu *vcpu); > static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags); > static void store_regs(struct kvm_vcpu *vcpu); > static int sync_regs(struct kvm_vcpu *vcpu); > +static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu); > +static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu); > > struct kvm_x86_ops *kvm_x86_ops __read_mostly; > EXPORT_SYMBOL_GPL(kvm_x86_ops); > @@ -2959,6 +2961,12 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > } > EXPORT_SYMBOL_GPL(kvm_get_msr_common); > > +static bool is_xsaves_msr(u32 index) > +{ > + return index == MSR_IA32_U_CET || > + (index >= MSR_IA32_PL0_SSP && index <= MSR_IA32_PL3_SSP); > +} > + > /* > * Read or write a bunch of msrs. All parameters are kernel addresses. > * > @@ -2969,11 +2977,30 @@ static int __msr_io(struct kvm_vcpu *vcpu, struct kvm_msrs *msrs, > int (*do_msr)(struct kvm_vcpu *vcpu, > unsigned index, u64 *data)) > { > + bool fpu_loaded = false; > int i; > + u64 cet_bits = XFEATURE_MASK_CET_USER | XFEATURE_MASK_CET_KERNEL; Dunno if the compiler will actually generate different code, but this can be a const. > + u64 host_xss = 0; > + > + for (i = 0; i < msrs->nmsrs; ++i) { > + if (!fpu_loaded && is_xsaves_msr(entries[i].index)) { > + if (!kvm_x86_ops->xsaves_supported() || > + !kvm_x86_ops->supported_xss()) The "!kvm_x86_ops->supported_xss()" is redundant with the host_xss check below. > + continue; Hmm, vmx_set_msr() should be checking host_xss, arguably we should call do_msr() and let it handle the bad MSR access. I don't have a strong opinion either way, practically speaking the end result will be the same. If we do want to handle a misbehaving userspace here, this should be 'break' instead of 'continue'. > + > + host_xss = kvm_x86_ops->supported_xss(); > > - for (i = 0; i < msrs->nmsrs; ++i) > + if ((host_xss & cet_bits) != cet_bits) I'm pretty sure this should check for either CET bit being set, not both, e.g. I assume it's possible to enable and expose XFEATURE_MASK_CET_USER but not XFEATURE_MASK_CET_KERNEL. So something like const u64 cet_bits = XFEATURE_MASK_CET_USER | XFEATURE_MASK_CET_KERNEL; const bool cet_supported = kvm_x86_ops->xsaves_supported() && (kvm_x86_ops->supported_xss() & cet_bits); for (i = 0; i < msrs->nmsrs; ++i) { if (!fpu_loaded && cet_supported && is_xsaves_msr(entries[i].index)) { kvm_load_guest_fpu(vcpu); fpu_loaded = true; } if (do_msr(vcpu, entries[i].index, &entries[i].data)) break; } or const u64 cet_bits = XFEATURE_MASK_CET_USER | XFEATURE_MASK_CET_KERNEL; for (i = 0; i < msrs->nmsrs; ++i) { if (!fpu_loaded && is_xsaves_msr(entries[i].index)) { if (!kvm_x86_ops->supported_xss() || !(kvm_x86_ops->supported_xss() & cet_bits)) break; kvm_load_guest_fpu(vcpu); fpu_loaded = true; } if (do_msr(vcpu, entries[i].index, &entries[i].data)) break; } > + continue; > + > + kvm_load_guest_fpu(vcpu); > + fpu_loaded = true; > + } > if (do_msr(vcpu, entries[i].index, &entries[i].data)) > break; > + } > + if (fpu_loaded) > + kvm_put_guest_fpu(vcpu); > > return i; > } > -- > 2.17.2 >