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client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by SJ5PEPF000001CF.mail.protection.outlook.com (10.167.242.43) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8445.10 via Frontend Transport; Tue, 11 Feb 2025 08:24:46 +0000 Received: from BLR-L1-NDADHANI (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Tue, 11 Feb 2025 02:24:42 -0600 From: Nikunj A Dadhania To: Tom Lendacky , , , CC: , , Subject: Re: [PATCH v2 3/4] KVM: SVM: Prevent writes to TSC MSR when Secure TSC is enabled In-Reply-To: <8ec1bef9-829d-4370-47f6-c94e794cc5d5@amd.com> References: <20250210092230.151034-1-nikunj@amd.com> <20250210092230.151034-4-nikunj@amd.com> <8ec1bef9-829d-4370-47f6-c94e794cc5d5@amd.com> Date: Tue, 11 Feb 2025 08:24:35 +0000 Message-ID: <85ed04ubwc.fsf@amd.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-ClientProxiedBy: SATLEXMB04.amd.com (10.181.40.145) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ5PEPF000001CF:EE_|PH7PR12MB6859:EE_ X-MS-Office365-Filtering-Correlation-Id: 2e07cc13-ef4a-4354-4004-08dd4a758b3b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|82310400026|36860700013|1800799024; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Feb 2025 08:24:46.2460 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 2e07cc13-ef4a-4354-4004-08dd4a758b3b X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ5PEPF000001CF.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB6859 Tom Lendacky writes: > On 2/10/25 03:22, Nikunj A Dadhania wrote: >> Disallow writes to MSR_IA32_TSC for Secure TSC enabled SNP guests, as such >> writes are not expected. Log the error and return #GP to the guest. > > Re-word this to make it a bit clearer about why this is needed. It is > expected that the guest won't write to MSR_IA32_TSC or, if it does, it > will ignore any writes to it and not exit to the HV. So this is catching > the case where that behavior is not occurring. > Sure, will update. >> >> Signed-off-by: Nikunj A Dadhania >> --- >> arch/x86/kvm/svm/svm.c | 11 +++++++++++ >> 1 file changed, 11 insertions(+) >> >> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c >> index d7a0428aa2ae..929f35a2f542 100644 >> --- a/arch/x86/kvm/svm/svm.c >> +++ b/arch/x86/kvm/svm/svm.c >> @@ -3161,6 +3161,17 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) >> >> svm->tsc_aux = data; >> break; >> + case MSR_IA32_TSC: >> + /* >> + * If Secure TSC is enabled, KVM doesn't expect to receive >> + * a VMEXIT for a TSC write, record the error and return a >> + * #GP >> + */ >> + if (vcpu->arch.guest_state_protected && snp_secure_tsc_enabled(vcpu->kvm)) { > > Does it matter if the VMSA has already been encrypted? Can this just be > > if (sev_snp_guest() && snp_secure_tsc_enabled(vcpu->kvm)) { > > ? > QEMU initializes the IA32_TSC MSR to zero resulting in the below error if I use the above. qemu-system-x86_64: error: failed to set MSR 0x10 to 0x0 qemu-system-x86_64: ../target/i386/kvm/kvm.c:3849: kvm_buf_set_msrs: Assertion `ret == cpu->kvm_msr_buf->nmsrs' failed. Once the guest state is protected, we do not expect any writes from VMM. Regards, Nikunj