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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6CCF1C433FE for ; Mon, 4 Oct 2021 16:11:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 579A461373 for ; Mon, 4 Oct 2021 16:11:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236587AbhJDQNP (ORCPT ); Mon, 4 Oct 2021 12:13:15 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:32055 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236624AbhJDQNE (ORCPT ); Mon, 4 Oct 2021 12:13:04 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633363875; 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=qHrvX3IT0PrHvWz0jB6gkvGTsIwTwVhbBS/SiQBSGZ0=; b=UXYdSXq7F5X7mixWKKdaMP551j5jiqOnC3qiTkLuUQhmju5XzcyuEELLhb1Ai6+xqtZSSf Rnb5WsYQa9JvtVCdyw3AfGSSSh1UdK4/g4KWGxXI2mbX8SmsdTZYRy3vYHcKzbwsRfwDGb k6PesqrH588hUAJGbp3gItFtrG8BPXc= 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-542-Pqy9iBFSOvKA0umJTgmjcg-1; Mon, 04 Oct 2021 12:11:14 -0400 X-MC-Unique: Pqy9iBFSOvKA0umJTgmjcg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F2AD6100C660; Mon, 4 Oct 2021 16:11:12 +0000 (UTC) Received: from vitty.brq.redhat.com (unknown [10.40.194.218]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1054E652AD; Mon, 4 Oct 2021 16:10:44 +0000 (UTC) From: Vitaly Kuznetsov To: kvm@vger.kernel.org, Paolo Bonzini Cc: Sean Christopherson , Wanpeng Li , Jim Mattson , Maxim Levitsky , linux-kernel@vger.kernel.org Subject: [PATCH v2 4/4] KVM: nVMX: Implement Enlightened MSR Bitmap feature Date: Mon, 4 Oct 2021 18:10:29 +0200 Message-Id: <20211004161029.641155-5-vkuznets@redhat.com> In-Reply-To: <20211004161029.641155-1-vkuznets@redhat.com> References: <20211004161029.641155-1-vkuznets@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 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 | 20 ++++++++++++++++++-- 2 files changed, 20 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c index 6f11cda2bfa4..a00de1dbec57 100644 --- a/arch/x86/kvm/hyperv.c +++ b/arch/x86/kvm/hyperv.c @@ -2516,6 +2516,8 @@ 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 34c580b5dbab..b36004503f75 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -608,15 +608,30 @@ 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) + goto out_clear_msr_bitmap_changed; + if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcs12->msr_bitmap), map)) return false; @@ -700,6 +715,7 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu, kvm_vcpu_unmap(vcpu, &to_vmx(vcpu)->nested.msr_bitmap_map, false); +out_clear_msr_bitmap_changed: vmx->nested.msr_bitmap_changed = false; return true; -- 2.31.1