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=-5.3 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 CE765C47257 for ; Mon, 4 May 2020 14:29:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B483D20752 for ; Mon, 4 May 2020 14:29:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729028AbgEDO3i (ORCPT ); Mon, 4 May 2020 10:29:38 -0400 Received: from mga12.intel.com ([192.55.52.136]:10186 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728486AbgEDO3i (ORCPT ); Mon, 4 May 2020 10:29:38 -0400 IronPort-SDR: DqN//+WXfewpoXY2ugTjMm6t3xEP6iMEgcDRBevVPTDROxHjOT1GLpmnt35r8z7hdIfr1sngUp 8urm3+dscnVg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 May 2020 07:29:37 -0700 IronPort-SDR: iDqMIApWMrLvqyrp4b+noLJWhA1sSSJaN1o4qQFAscjAq2F3HVn8fIQsk4NZNSGa3ScNI5X32X sl3/q3dfiOoA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,352,1583222400"; d="scan'208";a="460683383" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.152]) by fmsmga005.fm.intel.com with ESMTP; 04 May 2020 07:29:33 -0700 Date: Mon, 4 May 2020 07:29:33 -0700 From: Sean Christopherson To: Paolo Bonzini Cc: Alexander Graf , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, KarimAllah Raslan Subject: Re: [PATCH v2] KVM: nVMX: Skip IBPB when switching between vmcs01 and vmcs02 Message-ID: <20200504142933.GA16949@linux.intel.com> References: <20200501163117.4655-1-sean.j.christopherson@intel.com> <1de7b016-8bc9-23d4-7f8b-145c30d7e58a@amazon.com> <9d0d09da-3920-16d6-11ae-51b864171b66@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9d0d09da-3920-16d6-11ae-51b864171b66@redhat.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 Mon, May 04, 2020 at 03:12:36PM +0200, Paolo Bonzini wrote: > On 04/05/20 14:01, Alexander Graf wrote: > > I like the WARN_ON :). It should be almost free during execution, but > > helps us catch problems early. > > Yes, it's nice. I didn't mind the "buddy" argument either, but if we're > going to get a bool I prefer positive logic so I'd like to squash this: I don't love need_ibpb as a param name, it doesn't provide any information as to why the IBPB is needed. But, I can't come up with anything better that isn't absurdly long because e.g. "different_guest" isn't necessarily true in the vmx_vcpu_load() path. What about going the @buddy route and adding the comment and WARN in vmx_vcpu_load_vmcs()? E.g. prev = per_cpu(current_vmcs, cpu); if (prev != vmx->loaded_vmcs->vmcs) { per_cpu(current_vmcs, cpu) = vmx->loaded_vmcs->vmcs; vmcs_load(vmx->loaded_vmcs->vmcs); /* * No indirect branch prediction barrier needed when switching * the active VMCS within a guest, e.g. on nested VM-Enter. * The L1 VMM can protect itself with retpolines, IBPB or IBRS. */ if (!buddy || WARN_ON_ONCE(buddy->vmcs != prev)) indirect_branch_prediction_barrier(); } > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c > index b57420f3dd8f..299393750a18 100644 > --- a/arch/x86/kvm/vmx/nested.c > +++ b/arch/x86/kvm/vmx/nested.c > @@ -304,7 +304,13 @@ static void vmx_switch_vmcs(struct kvm_vcpu *vcpu, struct loaded_vmcs *vmcs) > prev = vmx->loaded_vmcs; > WARN_ON_ONCE(prev->cpu != cpu || prev->vmcs != per_cpu(current_vmcs, cpu)); > vmx->loaded_vmcs = vmcs; > - vmx_vcpu_load_vmcs(vcpu, cpu, true); > + > + /* > + * This is the same guest from our point of view, so no > + * indirect branch prediction barrier is needed. The L1 > + * guest can protect itself with retpolines, IBPB or IBRS. > + */ > + vmx_vcpu_load_vmcs(vcpu, cpu, false); > vmx_sync_vmcs_host_state(vmx, prev); > put_cpu(); > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 669e14947ba9..0f9c8d2dd7f6 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -1311,7 +1311,7 @@ static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu) > pi_set_on(pi_desc); > } > > -void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu, bool nested_switch) > +void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu, bool need_ibpb) > { > struct vcpu_vmx *vmx = to_vmx(vcpu); > bool already_loaded = vmx->loaded_vmcs->cpu == cpu; > @@ -1336,7 +1336,7 @@ void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu, bool nested_switch) > if (per_cpu(current_vmcs, cpu) != vmx->loaded_vmcs->vmcs) { > per_cpu(current_vmcs, cpu) = vmx->loaded_vmcs->vmcs; > vmcs_load(vmx->loaded_vmcs->vmcs); > - if (!nested_switch) > + if (need_ibpb) > indirect_branch_prediction_barrier(); > } > > @@ -1378,7 +1378,7 @@ void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu) > { > struct vcpu_vmx *vmx = to_vmx(vcpu); > > - vmx_vcpu_load_vmcs(vcpu, cpu, false); > + vmx_vcpu_load_vmcs(vcpu, cpu, true); > > vmx_vcpu_pi_load(vcpu, cpu); > > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h > index fa61dc802183..e584ee9b3e94 100644 > --- a/arch/x86/kvm/vmx/vmx.h > +++ b/arch/x86/kvm/vmx/vmx.h > @@ -320,7 +320,7 @@ struct kvm_vmx { > }; > > bool nested_vmx_allowed(struct kvm_vcpu *vcpu); > -void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu, bool nested_switch); > +void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu, bool need_ibpb); > void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu); > int allocate_vpid(void); > void free_vpid(int vpid); > > > Paolo >