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=-5.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 775FBC47254 for ; Mon, 4 May 2020 13:12:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4F7AC2073E for ; Mon, 4 May 2020 13:12:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Jow5aUhX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727930AbgEDNMn (ORCPT ); Mon, 4 May 2020 09:12:43 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:60037 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726404AbgEDNMm (ORCPT ); Mon, 4 May 2020 09:12:42 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588597960; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=3UJFfbQE2y0YksHkyDVD2IwXDk0FmannGZsgQWHPWN4=; b=Jow5aUhXFqee+eRcLAMAq5UETuixmXyqgHdu0QoEA0c8k2lcBo+oPyLmJKRT2js51czopQ yD8ipq1zGqit6OBYddqhfNGlIItTfE4QF8Z5+RVSaKTW5ZBuEKKzkeTao/LKkJQx4A18Oq Bp0sYTS1xWIhBwAAjp2I3hadlLHfKEE= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-106-SInlJcjyOImXARWx7ik6Dg-1; Mon, 04 May 2020 09:12:39 -0400 X-MC-Unique: SInlJcjyOImXARWx7ik6Dg-1 Received: by mail-wr1-f72.google.com with SMTP id p2so10683866wrx.12 for ; Mon, 04 May 2020 06:12:39 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=3UJFfbQE2y0YksHkyDVD2IwXDk0FmannGZsgQWHPWN4=; b=ggq1IGuDs2aP5s5LA2DliR6Apz1vwGo2OyfmV/H2vzdJ5tHFXo1UI6YhSwbs159K2z aH4ARYGsD7DLSuW+zTuClajGlBqI9erGSjh0NtcMYSeyrowtRVUiCnnp/7Q3NN71JxXj rQ1VWnUUjYbhJsWUi39YO0aqVMpQ6FP8pCVtfJ6b8VT+gHVBcl/N1xDRZ2+QryYMktVn kzamyCSazdDPDGACir+w3Rf9lA6Og3//5GP0qLCrPG+K9F2bWsa6L9FORPQ6Sb02HVfi mAL3HbBwLEbVxqxlImSXU3q6S+F/ReIxpSz5QyWB2fbNucQzEyxFMviTq7BmrPSLAQhF YaSg== X-Gm-Message-State: AGi0PubF+CwgsIYZrWg1gRMziWMdo9RpXkFja026e95FQlYxZ+IDFlcK SbYGajE/nN9/ajBMkRKigDK/Kiu+OwP+QzUXbUI88/qgD8tsagaeja1pw/1x3gth7l2/yxI185v wt8F+j2JQLhVaslIBtZ/oanu6 X-Received: by 2002:a5d:6a04:: with SMTP id m4mr20588291wru.326.1588597957908; Mon, 04 May 2020 06:12:37 -0700 (PDT) X-Google-Smtp-Source: APiQypJ1O81/J0JwkiZSh7+3W4ruk62C2ztVK4Zj9/OJqN1Gg3ctJQj8c3Zb9XuibDPMugA0aCXfZw== X-Received: by 2002:a5d:6a04:: with SMTP id m4mr20588269wru.326.1588597957696; Mon, 04 May 2020 06:12:37 -0700 (PDT) Received: from [192.168.178.58] ([151.20.132.175]) by smtp.gmail.com with ESMTPSA id h16sm20691024wrw.36.2020.05.04.06.12.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 May 2020 06:12:37 -0700 (PDT) Subject: Re: [PATCH v2] KVM: nVMX: Skip IBPB when switching between vmcs01 and vmcs02 To: Alexander Graf , Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, KarimAllah Raslan References: <20200501163117.4655-1-sean.j.christopherson@intel.com> <1de7b016-8bc9-23d4-7f8b-145c30d7e58a@amazon.com> From: Paolo Bonzini Message-ID: <9d0d09da-3920-16d6-11ae-51b864171b66@redhat.com> Date: Mon, 4 May 2020 15:12:36 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <1de7b016-8bc9-23d4-7f8b-145c30d7e58a@amazon.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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: 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