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=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 DC399C4332F for ; Fri, 10 Sep 2021 16:08:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C579361205 for ; Fri, 10 Sep 2021 16:08:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233345AbhIJQJP (ORCPT ); Fri, 10 Sep 2021 12:09:15 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:31780 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231270AbhIJQIJ (ORCPT ); Fri, 10 Sep 2021 12:08:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631290017; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=nZ9m8GB+SRNPd987F+aUm8xDcHRH1ey6FXHn0bKLQqE=; b=ZAEEHSF26rIODI/Txq4c/NPO9CFefxszbNfTTsMI6rZPKYYjmNnqU/smCD3Y6syPthppy1 GcBhZ/7wyCts2fMdpftfrlav+s5tyde2IdXgwP0fgCzMeGLrmcazkN25/8Yy7KBr331HMp gU1EE17FtMdcfyhRusks0Teed6zR0j8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-381-z7KQJQ2hP6S8PJA48x5-ug-1; Fri, 10 Sep 2021 12:06:51 -0400 X-MC-Unique: z7KQJQ2hP6S8PJA48x5-ug-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7871B1084682; Fri, 10 Sep 2021 16:06:50 +0000 (UTC) Received: from vitty.brq.redhat.com (unknown [10.40.192.108]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7D18B5C1A1; Fri, 10 Sep 2021 16:06:48 +0000 (UTC) From: Vitaly Kuznetsov To: kvm@vger.kernel.org, Paolo Bonzini Cc: Sean Christopherson , Wanpeng Li , Jim Mattson , linux-kernel@vger.kernel.org Subject: [PATCH 4/4] KVM: nVMX: Implement Enlightened MSR Bitmap feature Date: Fri, 10 Sep 2021 18:06:33 +0200 Message-Id: <20210910160633.451250-5-vkuznets@redhat.com> In-Reply-To: <20210910160633.451250-1-vkuznets@redhat.com> References: <20210910160633.451250-1-vkuznets@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Updating MSR bitmap for L2 is not cheap and rearly needed. TLFS for Hyper-V offers 'Enlightened MSR Bitmap' feature which allows L1 hypervisor to inform L0 when it changes MSR bitmap, this eliminates the need to examine L1's MSR bitmap for L2 every time when 'real' MSR bitmap for L2 gets constructed. Use 'vmx->nested.msr_bitmap_changed' flag to implement the feature. Note, KVM already uses 'Enlightened MSR bitmap' feature when it runs as a nested hypervisor on top of Hyper-V. The newly introduced feature is going to be used by Hyper-V guests on KVM. When the feature is enabled for Win10+WSL2, it shaves off around 700 CPU cycles from a nested vmexit cost (tight cpuid loop test). Signed-off-by: Vitaly Kuznetsov --- arch/x86/kvm/hyperv.c | 2 ++ arch/x86/kvm/vmx/nested.c | 19 +++++++++++++++++-- 2 files changed, 19 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c index 232a86a6faaf..7124dbe79ac2 100644 --- a/arch/x86/kvm/hyperv.c +++ b/arch/x86/kvm/hyperv.c @@ -2517,6 +2517,8 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid, case HYPERV_CPUID_NESTED_FEATURES: ent->eax = evmcs_ver; + if (evmcs_ver) + ent->eax |= HV_X64_NESTED_MSR_BITMAP; break; diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 42cd95611892..5ac5ba2f6191 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -607,15 +607,30 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12) { int msr; + struct vcpu_vmx *vmx = to_vmx(vcpu); unsigned long *msr_bitmap_l1; - unsigned long *msr_bitmap_l0 = to_vmx(vcpu)->nested.vmcs02.msr_bitmap; - struct kvm_host_map *map = &to_vmx(vcpu)->nested.msr_bitmap_map; + unsigned long *msr_bitmap_l0 = vmx->nested.vmcs02.msr_bitmap; + struct hv_enlightened_vmcs *evmcs = vmx->nested.hv_evmcs; + struct kvm_host_map *map = &vmx->nested.msr_bitmap_map; /* Nothing to do if the MSR bitmap is not in use. */ if (!cpu_has_vmx_msr_bitmap() || !nested_cpu_has(vmcs12, CPU_BASED_USE_MSR_BITMAPS)) return false; + /* + * MSR bitmap update can be skipped when: + * - MSR bitmap for L1 hasn't changed. + * - Nested hypervisor (L1) is attempting to launch the same L2 as + * before. + * - Nested hypervisor (L1) has enabled 'Enlightened MSR Bitmap' feature + * and tells KVM (L0) there were no changes in MSR bitmap for L2. + */ + if (!vmx->nested.msr_bitmap_changed && evmcs && + evmcs->hv_enlightenments_control.msr_bitmap && + evmcs->hv_clean_fields & HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP) + return true; + if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcs12->msr_bitmap), map)) return false; -- 2.31.1