From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6C84A4431 for ; Wed, 15 Mar 2023 12:24:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E821EC4339C; Wed, 15 Mar 2023 12:24:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1678883053; bh=/FPtLfzfoRc/NvT4kuMLvLt47hT6DUMDV0R/4baSISE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=NZ/IPi7gTiU/hC12zxMFAvO2YXo5khqMpBsvu/WH8RaxXMmlYKTsvtZZxX0kNaVDN 0pJI6d8zR2lQ6riUoQsNFAggm14cFGNFlqbYz1SYwaD/1s9EW3hSf2Mpy9ws47ZngF Dq6I3lNGr1Yf/w6/bCpG5rhtR1DP9rWDhB/RH8eM= 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 5.10 101/104] KVM: nVMX: Dont use Enlightened MSR Bitmap for L3 Date: Wed, 15 Mar 2023 13:13:12 +0100 Message-Id: <20230315115736.287969497@linuxfoundation.org> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230315115731.942692602@linuxfoundation.org> References: <20230315115731.942692602@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 @@ -2725,15 +2725,6 @@ 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)); @@ -7029,6 +7020,19 @@ 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);