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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 BN2PEPF00004FC0.mail.protection.outlook.com (10.167.243.186) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8534.20 via Frontend Transport; Mon, 10 Mar 2025 06:45:47 +0000 Received: from gomati.amd.com (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; Mon, 10 Mar 2025 01:45:44 -0500 From: Nikunj A Dadhania To: , , CC: , , , , Subject: [PATCH v4 4/5] KVM: SVM: Prevent writes to TSC MSR when Secure TSC is enabled Date: Mon, 10 Mar 2025 12:15:21 +0530 Message-ID: <20250310064522.14100-3-nikunj@amd.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250310064522.14100-1-nikunj@amd.com> References: <20250310063938.13790-1-nikunj@amd.com> <20250310064522.14100-1-nikunj@amd.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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: BN2PEPF00004FC0:EE_|CH2PR12MB9541:EE_ X-MS-Office365-Filtering-Correlation-Id: 34968d86-b217-40cf-71d6-08dd5f9f308c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|36860700013|82310400026|376014; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Mar 2025 06:45:47.4959 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 34968d86-b217-40cf-71d6-08dd5f9f308c 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: BN2PEPF00004FC0.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR12MB9541 Disallow writes to MSR_IA32_TSC for Secure TSC enabled SNP guests. Even if KVM attempts to emulate such writes, TSC calculation will ignore the TSC_SCALE and TSC_OFFSET present in the VMCB. Instead, it will use GUEST_TSC_SCALE and GUEST_TSC_OFFSET stored in the VMSA. Additionally, incorporate a check for protected guest state to allow the VMM to initialize the TSC MSR. Signed-off-by: Nikunj A Dadhania --- arch/x86/kvm/svm/svm.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index e65721db1f81..1652848b0240 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -3161,6 +3161,25 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) svm->tsc_aux = data; break; + case MSR_IA32_TSC: + /* + * For Secure TSC enabled VM, do not emulate TSC write as the + * TSC calculation ignores the TSC_OFFSET and TSC_SCALE control + * fields. + * + * Guest writes: Record the error and return a #GP. + * Host writes are ignored. + */ + if (snp_secure_tsc_enabled(vcpu->kvm)) { + if (!msr->host_initiated) { + vcpu_unimpl(vcpu, "unimplemented IA32_TSC for Secure TSC\n"); + return 1; + } else + return 0; + } + + ret = kvm_set_msr_common(vcpu, msr); + break; case MSR_IA32_DEBUGCTLMSR: if (!lbrv) { kvm_pr_unimpl_wrmsr(vcpu, ecx, data);