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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Jul 2025 04:12:25.9363 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 6f2a1987-14fb-4a16-8bfa-08ddc03124da 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: SJ1PEPF00001CE1.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB6460 Content-Type: text/plain; charset="utf-8" From: Sean Christopherson For Secure TSC enabled guests, don't panic when a guest writes to intercepted GUEST_TSC_FREQ MSR. Instead, ignore writes to GUEST_TSC_FREQ, similar to MSR_IA32_TSC, and log a warning instead. Only terminate the guest when reading from intercepted GUEST_TSC_FREQ MSR with Secure TSC enabled, as this indicates an unexpected hypervisor configuration. Signed-off-by: Sean Christopherson Signed-off-by: Nikunj A Dadhania --- arch/x86/coco/sev/vc-handle.c | 23 ++++++++++------------- 1 file changed, 10 insertions(+), 13 deletions(-) diff --git a/arch/x86/coco/sev/vc-handle.c b/arch/x86/coco/sev/vc-handle.c index faf1fce89ed4..581e34083321 100644 --- a/arch/x86/coco/sev/vc-handle.c +++ b/arch/x86/coco/sev/vc-handle.c @@ -376,24 +376,21 @@ static enum es_result __vc_handle_secure_tsc_msrs(str= uct pt_regs *regs, bool wri u64 tsc; =20 /* - * GUEST_TSC_FREQ should not be intercepted when Secure TSC is enabled. - * Terminate the SNP guest when the interception is enabled. + * Writing to MSR_IA32_TSC can cause subsequent reads of the TSC to + * return undefined values, and GUEST_TSC_FREQ is read-only. Ignore + * all writes, but WARN to log the kernel bug. */ - if (regs->cx =3D=3D MSR_AMD64_GUEST_TSC_FREQ) - return ES_VMM_ERROR; + if (WARN_ON_ONCE(write)) + return ES_OK; =20 /* - * 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_ordered(). + * GUEST_TSC_FREQ read should not be intercepted when Secure TSC is + * enabled. Terminate the SNP guest when the interception is enabled. */ - if (write) { - WARN_ONCE(1, "TSC MSR writes are verboten!\n"); - return ES_OK; - } + if (regs->cx =3D=3D MSR_AMD64_GUEST_TSC_FREQ) + return ES_VMM_ERROR; =20 + /* Reads of MSR_IA32_TSC should return the current TSC value. */ tsc =3D rdtsc_ordered(); regs->ax =3D lower_32_bits(tsc); regs->dx =3D upper_32_bits(tsc); --=20 2.43.0