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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D84D5C61DA4 for ; Wed, 15 Mar 2023 12:31:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232462AbjCOMbx (ORCPT ); Wed, 15 Mar 2023 08:31:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40938 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232369AbjCOMbi (ORCPT ); Wed, 15 Mar 2023 08:31:38 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2D4C88C53C for ; Wed, 15 Mar 2023 05:30:55 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 87E2061D26 for ; Wed, 15 Mar 2023 12:30:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9E837C433EF; Wed, 15 Mar 2023 12:30:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1678883455; bh=8sqsLCMpq3uPdTsdnkCMLX3RmGe0OSwfT+WahweiIuA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TDsQGBlpek4uX2AmCLEKRmIAsBeAKaSHsTB6CyyWgsiYz+q2ElmUl1QfT0RZlb5Z+ RONikEUEwCuCKz9OJDy731yu9k1GpcLBmqKbPvDtvzGrfj8FPaNJkM6q1uZwpRIPZq w/TgeQLNaTlw0ZKSI4/+9ag+6zwc0vUTqTL8A2fM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Vitaly Kuznetsov , Paolo Bonzini , Alexandru Matei Subject: [PATCH 5.15 143/145] KVM: nVMX: Dont use Enlightened MSR Bitmap for L3 Date: Wed, 15 Mar 2023 13:13:29 +0100 Message-Id: <20230315115743.623834371@linuxfoundation.org> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230315115738.951067403@linuxfoundation.org> References: <20230315115738.951067403@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Vitaly Kuznetsov commit 250552b925ce400c17d166422fde9bb215958481 upstream. 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 Message-Id: <20211129094704.326635-2-vkuznets@redhat.com> Signed-off-by: Paolo Bonzini Signed-off-by: Alexandru Matei Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/vmx/vmx.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-) --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -2739,15 +2739,6 @@ int alloc_loaded_vmcs(struct 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)); @@ -6969,6 +6960,19 @@ static int vmx_create_vcpu(struct kvm_vc if (err < 0) goto free_pml; + /* + * Use Hyper-V 'Enlightened MSR Bitmap' feature when KVM runs as a + * nested (L1) hypervisor and Hyper-V in L0 supports it. Enable the + * feature only for vmcs01, KVM currently isn't equipped to realize any + * performance benefits from enabling it for vmcs02. + */ + if (IS_ENABLED(CONFIG_HYPERV) && static_branch_unlikely(&enable_evmcs) && + (ms_hyperv.nested_features & HV_X64_NESTED_MSR_BITMAP)) { + struct hv_enlightened_vmcs *evmcs = (void *)vmx->vmcs01.vmcs; + + evmcs->hv_enlightenments_control.msr_bitmap = 1; + } + /* The MSR bitmap starts with all ones */ bitmap_fill(vmx->shadow_msr_intercept.read, MAX_POSSIBLE_PASSTHROUGH_MSRS); bitmap_fill(vmx->shadow_msr_intercept.write, MAX_POSSIBLE_PASSTHROUGH_MSRS);