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 E2588C433F5 for ; Mon, 4 Oct 2021 16:10:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C690F613A1 for ; Mon, 4 Oct 2021 16:10:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236486AbhJDQMb (ORCPT ); Mon, 4 Oct 2021 12:12:31 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:47347 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236457AbhJDQM3 (ORCPT ); Mon, 4 Oct 2021 12:12:29 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633363840; 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=lr6YDui4wbSQYDYrfzfOyejVZAp+ytZycUnTCmtdldo=; b=F2rDV2roiB492XYS+7eTJ3BXvHmw1qCxIjt/NIQIUNjctSsl3hgHPU8ZThcrBIh6c67+hG 6d/tfcXuez8nvnnjFinJptJH40zH6AikfS6VoWCK6f+NRhy2GxB5p9HsNOwVtXT0HY44wv TBIEAepBHbHXJPf3PN/gJmrUXwK6Swg= 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-109-BwvZyfmKOiq1gq8XejvkSQ-1; Mon, 04 Oct 2021 12:10:38 -0400 X-MC-Unique: BwvZyfmKOiq1gq8XejvkSQ-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 A249A100C660; Mon, 4 Oct 2021 16:10:37 +0000 (UTC) Received: from vitty.brq.redhat.com (unknown [10.40.194.218]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2DEAB652AB; Mon, 4 Oct 2021 16:10:34 +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 1/4] KVM: nVMX: Don't use Enlightened MSR Bitmap for L3 Date: Mon, 4 Oct 2021 18:10:26 +0200 Message-Id: <20211004161029.641155-2-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 When KVM runs as a nested hypervisor on top of Hyper-V it uses Enlightened VMCS and enables Enlightened MSR Bitmap feature for its L1s and L2s (which are actually L2s and L3s from Hyper-V's perspective). When MSR bitmap is updated, KVM has to reset HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP from clean fields to make Hyper-V aware of the change. For KVM's L1s, this is done in vmx_disable_intercept_for_msr()/vmx_enable_intercept_for_msr(). MSR bitmap for L2 is build in nested_vmx_prepare_msr_bitmap() by blending MSR bitmap for L1 and L1's idea of MSR bitmap for L2. KVM, however, doesn't check if the resulting bitmap is different and never cleans HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP in eVMCS02. This is incorrect and may result in Hyper-V missing the update. The issue could've been solved by calling evmcs_touch_msr_bitmap() for eVMCS02 from nested_vmx_prepare_msr_bitmap() unconditionally but doing so would not give any performance benefits (compared to not using Enlightened MSR Bitmap at all). 3-level nesting is also not a very common setup nowadays. Don't enable 'Enlightened MSR Bitmap' feature for KVM's L2s (real L3s) for now. Signed-off-by: Vitaly Kuznetsov Reviewed-by: Maxim Levitsky --- arch/x86/kvm/vmx/vmx.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 1c8b2b6e7ed9..e82cdde58119 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -2655,15 +2655,6 @@ int alloc_loaded_vmcs(struct loaded_vmcs *loaded_vmcs) if (!loaded_vmcs->msr_bitmap) goto out_vmcs; memset(loaded_vmcs->msr_bitmap, 0xff, PAGE_SIZE); - - if (IS_ENABLED(CONFIG_HYPERV) && - static_branch_unlikely(&enable_evmcs) && - (ms_hyperv.nested_features & HV_X64_NESTED_MSR_BITMAP)) { - struct hv_enlightened_vmcs *evmcs = - (struct hv_enlightened_vmcs *)loaded_vmcs->vmcs; - - evmcs->hv_enlightenments_control.msr_bitmap = 1; - } } memset(&loaded_vmcs->host_state, 0, sizeof(struct vmcs_host_state)); @@ -6903,6 +6894,18 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu) vmx->loaded_vmcs = &vmx->vmcs01; + /* + * Use Hyper-V 'Enlightened MSR Bitmap' feature when KVM runs as a + * nested (L1) hypervisor and Hyper-V in L0 supports it. + */ + if (IS_ENABLED(CONFIG_HYPERV) && static_branch_unlikely(&enable_evmcs) + && (ms_hyperv.nested_features & HV_X64_NESTED_MSR_BITMAP)) { + struct hv_enlightened_vmcs *evmcs = + (struct hv_enlightened_vmcs *)vmx->loaded_vmcs->vmcs; + + evmcs->hv_enlightenments_control.msr_bitmap = 1; + } + if (cpu_need_virtualize_apic_accesses(vcpu)) { err = alloc_apic_access_page(vcpu->kvm); if (err) -- 2.31.1