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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 27AD0C07E99 for ; Mon, 12 Jul 2021 09:23:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0FF0560FF0 for ; Mon, 12 Jul 2021 09:23:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350679AbhGLJ0p (ORCPT ); Mon, 12 Jul 2021 05:26:45 -0400 Received: from mga09.intel.com ([134.134.136.24]:54855 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1387166AbhGLJZ2 (ORCPT ); Mon, 12 Jul 2021 05:25:28 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10042"; a="209923690" X-IronPort-AV: E=Sophos;i="5.84,232,1620716400"; d="scan'208";a="209923690" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Jul 2021 02:22:29 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.84,232,1620716400"; d="scan'208";a="502065850" Received: from michael-optiplex-9020.sh.intel.com (HELO localhost) ([10.239.159.182]) by fmsmga002.fm.intel.com with ESMTP; 12 Jul 2021 02:22:23 -0700 Date: Mon, 12 Jul 2021 17:36:26 +0800 From: Yang Weijiang To: Jim Mattson Cc: Yang Weijiang , pbonzini@redhat.com, seanjc@google.com, vkuznets@redhat.com, wei.w.wang@intel.com, like.xu.linux@gmail.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Like Xu Subject: Re: [PATCH v5 05/13] KVM: vmx/pmu: Emulate MSR_ARCH_LBR_CTL for guest Arch LBR Message-ID: <20210712093626.GC12162@intel.com> References: <1625825111-6604-1-git-send-email-weijiang.yang@intel.com> <1625825111-6604-6-git-send-email-weijiang.yang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 09, 2021 at 02:55:35PM -0700, Jim Mattson wrote: > On Fri, Jul 9, 2021 at 2:51 AM Yang Weijiang wrote: > > > > From: Like Xu > > > > Arch LBRs are enabled by setting MSR_ARCH_LBR_CTL.LBREn to 1. A new guest > > state field named "Guest IA32_LBR_CTL" is added to enhance guest LBR usage. > > When guest Arch LBR is enabled, a guest LBR event will be created like the > > model-specific LBR does. Clear guest LBR enable bit on host PMI handling so > > guest can see expected config. > > > > On processors that support Arch LBR, MSR_IA32_DEBUGCTLMSR[bit 0] has no > > meaning. It can be written to 0 or 1, but reads will always return 0. > > Like IA32_DEBUGCTL, IA32_ARCH_LBR_CTL msr is also reserved on INIT. > > I suspect you mean "preserved" rather than "reserved." Yes, should be preserved. > > > Signed-off-by: Like Xu > > Signed-off-by: Yang Weijiang > > --- > > arch/x86/events/intel/lbr.c | 2 -- > > arch/x86/include/asm/msr-index.h | 1 + > > arch/x86/include/asm/vmx.h | 2 ++ > > arch/x86/kvm/vmx/pmu_intel.c | 31 ++++++++++++++++++++++++++----- > > arch/x86/kvm/vmx/vmx.c | 9 +++++++++ > > 5 files changed, 38 insertions(+), 7 deletions(-) > > > > > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c > > index da68f0e74702..4500c564c63a 100644 > > --- a/arch/x86/kvm/vmx/pmu_intel.c > > +++ b/arch/x86/kvm/vmx/pmu_intel.c > > @@ -19,6 +19,11 @@ > > #include "pmu.h" > > > > #define MSR_PMC_FULL_WIDTH_BIT (MSR_IA32_PMC0 - MSR_IA32_PERFCTR0) > > +/* > > + * Regardless of the Arch LBR or legacy LBR, when the LBR_EN bit 0 of the > > + * corresponding control MSR is set to 1, LBR recording will be enabled. > > + */ > > Is this comment misplaced? It doesn't seem to have anything to do with > the macro being defined below. Agree, will put this in commit message. > > > @@ -458,6 +467,14 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > > lbr_desc->records.nr = data; > > lbr_desc->arch_lbr_reset = true; > > return 0; > > + case MSR_ARCH_LBR_CTL: > > + if (data & ~KVM_ARCH_LBR_CTL_MASK) > > Is a static mask sufficient? Per the Intel® Architecture Instruction > Set Extensions and Future Features Programming Reference, some of > these bits may not be supported on all microarchitectures. See Table > 7-8. CPUID Leaf 01CH Enumeration of Architectural LBR Capabilities. Yes, more sanity checks are required, thanks! > > > + break; > > + vmcs_write64(GUEST_IA32_LBR_CTL, data); > > + if (intel_pmu_lbr_is_enabled(vcpu) && !lbr_desc->event && > > + (data & ARCH_LBR_CTL_LBREN)) > > + intel_pmu_create_guest_lbr_event(vcpu); > > Nothing has to be done when the LBREN bit goes from 1 to 0? Need to release the event and reset related flag when the bit goes from 1 to 0. Thanks! > > > + return 0; > > default: > > if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) || > > (pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) { > > Per the Intel® Architecture Instruction Set Extensions and Future > Features Programming Reference, "IA32_LBR_CTL.LBREn is saved and > cleared on #SMI, and restored on RSM." I don't see that happening > anywhere. That manual also says, "On a warm reset...IA32_LBR_CTL.LBREn > is cleared to 0, disabling LBRs." I don't see that happening either. Yes, I'll add related code to make it consistent with spec, thanks! > > I have a question about section 7.1.4.4 in that manual. It says, "On a > debug breakpoint event (#DB), IA32_LBR_CTL.LBREn is cleared." When, > exactly, does that happen? In particular, if kvm synthesizes such an > event (for example, in kvm_vcpu_do_singlestep), does > IA32_LBR_CTL.LBREn automatically get cleared (after loading the guest > IA32_LBR_CTL value from the VMCS)? Or does kvm need to explicitly > clear that bit in the VMCS before injecting the #DB? OK, I don't have answer now, will ask the Arch to get clear answer on this, thanks for raising the question!