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Y. Srinivasan" , Haiyang Zhang , "Wei Liu" , Dexuan Cui , Long Li , Ajay Kaher , Alexey Makhalov , Jan Kiszka , "Andy Lutomirski" , Peter Zijlstra , Juergen Gross , Daniel Lezcano , John Stultz CC: Shuah Khan , "H. Peter Anvin" , Vitaly Kuznetsov , Broadcom internal kernel review list , Boris Ostrovsky , Stephen Boyd , , , , , , , , Tom Lendacky , David Woodhouse , David Woodhouse , Michael Kelley , Thomas Gleixner References: <20260701193212.749551-1-seanjc@google.com> <20260701193212.749551-48-seanjc@google.com> Content-Language: en-US From: "Nikunj A. Dadhania" In-Reply-To: <20260701193212.749551-48-seanjc@google.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CY4PEPF0000EE3F:EE_|DS7PR12MB6287:EE_ X-MS-Office365-Filtering-Correlation-Id: 0ed22401-cf4b-4db4-f9c4-08dedcade4a8 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|1800799024|32650700020|23010399003|376014|7416014|36860700016|11063799006|56012099006|4143699003|22082099003|18002099003|921020; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(82310400026)(1800799024)(32650700020)(23010399003)(376014)(7416014)(36860700016)(11063799006)(56012099006)(4143699003)(22082099003)(18002099003)(921020);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: zaoEsGbRqKJtvHxF7Cp7T4h6fpbC+IQ1bcqTKUXjPqC4nToKNP1pgGG2dGwPmwBX/uwMDmU8HMTRiIY9QNanhb36RkGJh7po0Uiaf2z8+eMG8tmP9UpYZrBL1I1DjnTDzRfF7JZWMRjjx8m1O0B857aEZehV5lPOVmYQ+J8y1HmVMvacnQHSXRUzqGg2poz48mf3EQ0y6WSIgktjX0zYcnseZGoSqtznKBhM6M28pO7HjUKz8qfBQAOYtOXu2S6rx8T4zuK8hbwFEHIJ9mcyc0SbVaup1U77Syy8gzP4HbY9H2H5x27dQsqMvo66BKOHHs/zuC5vP99APeLkbuk0gIsP0OzYP5CgcwS2liH8jhsy7fa2isulNyYhT+Zb05BcHP+UzKlo4IyzmX5Bx7f1W93GIo1H0HNVW90gIFmhSzSwtf3k2dk7GTPiS3z3FEcf X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Jul 2026 05:00:55.6041 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 0ed22401-cf4b-4db4-f9c4-08dedcade4a8 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=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CY4PEPF0000EE3F.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR12MB6287 On 7/2/2026 1:02 AM, Sean Christopherson wrote: > Silently ignore attempts to switch to a paravirt sched_clock when running > as a CoCo guest with trusted TSC. In hand-wavy theory, a misbehaving > hypervisor could attack the guest by manipulating the PV clock to affect > guest scheduling in some weird and/or predictable way. More importantly, > reading TSC on such platforms is faster than any PV clock, and sched_clock > is all about speed. > > Reviewed-by: David Woodhouse > Signed-off-by: Sean Christopherson Reviewed-by: Nikunj A Dadhania > --- > arch/x86/kernel/tsc.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c > index 012321fed5e5..a146fc7b5e74 100644 > --- a/arch/x86/kernel/tsc.c > +++ b/arch/x86/kernel/tsc.c > @@ -283,6 +283,15 @@ bool using_native_sched_clock(void) > int __init __paravirt_set_sched_clock(u64 (*func)(void), bool stable, > void (*save)(void), void (*restore)(void)) > { > + /* > + * Don't replace TSC with a PV clock when running as a CoCo guest and > + * the TSC is secure/trusted; PV clocks are emulated by the hypervisor, > + * which isn't in the guest's TCB. > + */ > + if (cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC) || > + boot_cpu_has(X86_FEATURE_TDX_GUEST)) > + return -EPERM; > + > if (!stable) > clear_sched_clock_stable(); >