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Received-SPF: Pass (protection.outlook.com: domain of amd.com designates 165.204.84.17 as permitted sender) receiver=protection.outlook.com; client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by CO1NAM11FT016.mail.protection.outlook.com (10.13.175.141) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.6043.21 via Frontend Transport; Mon, 30 Jan 2023 12:04:43 +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 15.1.2375.34; Mon, 30 Jan 2023 06:04:39 -0600 From: Nikunj A Dadhania To: , CC: , , , , , , , , , , , , Subject: [RFC PATCH 07/11] x86/sev: Change TSC MSR behavior for Secure TSC enabled guests Date: Mon, 30 Jan 2023 17:33:23 +0530 Message-ID: <20230130120327.977460-8-nikunj@amd.com> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20230130120327.977460-1-nikunj@amd.com> References: <20230130120327.977460-1-nikunj@amd.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB03.amd.com (10.181.40.144) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO1NAM11FT016:EE_|CH0PR12MB5330:EE_ X-MS-Office365-Filtering-Correlation-Id: e136874d-1a2d-4bee-fc56-08db02ba2cb3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Jan 2023 12:04:43.8504 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: e136874d-1a2d-4bee-fc56-08db02ba2cb3 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: CO1NAM11FT016.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH0PR12MB5330 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Secure TSC enabled guests should not write MSR_IA32_TSC(10H) register as the subsequent TSC value reads are undefined. MSR_IA32_TSC related accesses should not exit to the hypervisor for such guests. Accesses to MSR_IA32_TSC needs special handling in the #VC handler for the guests with Secure TSC enabled. Writes to MSR_IA32_TSC should be ignored, and reads of MSR_IA32_TSC should return the result of the RDTSC instruction. Signed-off-by: Nikunj A Dadhania --- arch/x86/kernel/sev.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c index be49a9aa3a2e..3ca87cd4548e 100644 --- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c @@ -1601,6 +1601,30 @@ static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt) /* Is it a WRMSR? */ exit_info_1 = (ctxt->insn.opcode.bytes[1] == 0x30) ? 1 : 0; + /* + * TSC related accesses should not exit to the hypervisor when a + * guest is executing with SecureTSC enabled, so special handling + * is required for accesses of MSR_IA32_TSC: + * + * Writes: Writing to MSR_IA32_TSC can cause subsequent reads + * of the TSC to return undefined values, so ignore all + * writes. + * Reads: Reads of MSR_IA32_TSC should return the current TSC + * value, use the value returned by RDTSC. + */ + if (regs->cx == MSR_IA32_TSC && (sev_status & MSR_AMD64_SNP_SECURE_TSC)) { + u64 tsc; + + if (exit_info_1) + return ES_OK; + + tsc = rdtsc(); + regs->ax = UINT_MAX & tsc; + regs->dx = UINT_MAX & (tsc >> 32); + + return ES_OK; + } + ghcb_set_rcx(ghcb, regs->cx); if (exit_info_1) { ghcb_set_rax(ghcb, regs->ax); -- 2.32.0