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Peter Anvin" , Maxim Levitsky , , , Matteo Rizzo , References: <20251101000241.3764458-1-jmattson@google.com> Content-Language: en-US From: Shivansh Dhiman In-Reply-To: <20251101000241.3764458-1-jmattson@google.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PEPF0000009E:EE_|CY8PR12MB7660:EE_ X-MS-Office365-Filtering-Correlation-Id: 86550045-381e-4bd1-3013-08de1d4ed213 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700013|1800799024|376014|7416014|82310400026|7053199007; X-Microsoft-Antispam-Message-Info: =?utf-8?B?SVlSNUZCRVdoa2FTMHc0REdoQ2Z6VDRjNXdyMVFXT2kxY0ZFTm5yWWVpWTNB?= =?utf-8?B?ZkhqR2RZaGlHK2ZrNUd2dUtqd3FmeUlmTVExZWRFakM2UVpsSk91bmsxcENC?= =?utf-8?B?aUk1WmJXMTkzbWp6QVVma2ZaWkFGQkRxZ3VDREx1WGdGaTlBaXZBOVRqNGxU?= =?utf-8?B?RGFudEFMeTN5UEQrMExXTjYzd0piZkcrMHVFaTZSVHppcUhNUUtlOVEreUUz?= =?utf-8?B?MUpHL2hBdWlzMTllV1YvcUlGbWcvTGR6N1ZLV2dWNkZhdnN4NjM1aEhMNFpa?= =?utf-8?B?aWNHcnI1OTA1MHB1cnhmTmZNVktJQlRTVkdFd1BKY1V6cDdOZnQ4dkJleVdZ?= =?utf-8?B?NnAwTWJJdGE3ZDNXb2JjaVF5Ukx2STJKbFQ3SmdqZmdpOHhpQnVlYUxkL2tQ?= =?utf-8?B?TnlPS3RWSjRGZjdwUTRlVGE1MEdGZW9GeHFxVmsxRmJYclVLQXdEMDR0Smxw?= =?utf-8?B?UnYybzExMzVYM3UvU0lXUTJ6VFZuYUJXZWNWK0k0YkVKY2MrQTV1dnRpZHZp?= =?utf-8?B?SVJ1QTQ4VDRZa0d5b0xXSnpUVEc1Y2Z2Y3ZSdWlpQjgyLytUWndodVZya25x?= =?utf-8?B?OFVDcWlodCsvUENaZGt4MTRQN2wwandrWVJReW0xWDM1ampBamVEbnkyTmZJ?= =?utf-8?B?YUwwbnMxVHo4NHMzZmtOV05XckI0QWVSdFhxYkl1VDVPbjBTUTIxM2xSUUtH?= =?utf-8?B?bktTWVpad2gyV20wTHFXeUV5V2FtMUIwZDI2WEF0RTgyMVY3ZitKV1RQVnVT?= =?utf-8?B?RmMwdFVidW16ZnBYOHdmU3FBbEVscTBIYlZ2NjR2WjF5VHhYY0NwMnQ5WHZX?= =?utf-8?B?ZVRLRzBhRk1zQzYrMkdZMzM1bytmbUdoakxmckN5U1FzdkxIUmxFY1k3Z2Vx?= =?utf-8?B?cnJGMy8wKytxTDJESFVMM2dkM2FNRlVlQVE3SUhSZk9vVjRxRkxCUGw3Um1E?= =?utf-8?B?ZVltRG9RamoveU9mZzNQaEwzNkVzWmk4N1l5T0VQUVRWc0RqeU55aUR1TFZt?= =?utf-8?B?Z1dtVXVUeU1iUGViem91MjRCMmtaak4zclRBT1E4Y04vQUF3Y3FZOGc1NEUy?= =?utf-8?B?ek1HSkpBUHcyM1hBdUpnYXFQSTAvZ0VPa2ptV2dDTndVK2JVeW5wOWpGWXlE?= =?utf-8?B?TjM3dExUNzV3akk1ejZvdEVtMzFNc3c5WElEazlFNWl5TTZTWTdZd1lUaEh3?= =?utf-8?B?cXRIQ3c5eG9pU1JLUGpySmxaczFQR1F3SngrNEVPdDUvVDlnQlBocTZrOGNj?= =?utf-8?B?L3ptaS9YTTFZRVFSeUk1RlZUeGFKeTl5UUx4STRTbUxTV2VScDdneTZpQ09y?= =?utf-8?B?dXpyVDFPNEh0WTZEdDVBOFhQVC9WV04yYlJZbjMzelpNaURoNjQ2aEI4TTdT?= =?utf-8?B?dThPYXlOMk9YSnVrbEx6V3dVZk9pWTVwSmdNOWFwRWNiMUQ3Z3UrU0NjdXFQ?= =?utf-8?B?VEJPYmphM2M1cVk1WVhoZFZkRk14SjBTbTd1d1N3VGhVQ2J3OEJyZllZcGlZ?= =?utf-8?B?VjdKVVlFYk5qRmFrK0RhSURZTGYraXFFUnFNT2FIVTNUcDZQMFVGWHIxZUF1?= =?utf-8?B?cXk4bFMwS2FXWi9TdEZNMEhPN3o5V3VZczVHaTluK2lwbHJtbEtyaElwN29n?= =?utf-8?B?S1lRMUJIS0RMei9OS0VCSmswbXMyRytzNUtDS0VOay9CSHZCSVpzLzliTENy?= =?utf-8?B?b2VqL1grNlpOSUN0bEJLeE9aVjNXSk1yQ2VYOElMWU9pV2E0S2w1MiszbkNi?= =?utf-8?B?N1JnK1JIamNNdm1XRi8zOFhkbmFLSVY3YTFpa1lnODdXVE0raHpLS3RjN0NS?= =?utf-8?B?MWJjY0xmUTdOK2w4Vy9ZSW0rSmZNZ0hDVFRmV1kxRFBPSkIydm5rSWxUWmpY?= =?utf-8?B?eXVtSjNCa014VHJuVE9TSGZJZUdZd0R6cUhra0t1YzkrYzFrRkc2NzMzRmll?= =?utf-8?B?WHcvd0hpWGY0OUZyanhNekkrbU9KNFRRWFRCNFFYVGZPd2Z6bCs5RXBnTzhi?= =?utf-8?B?NDhkakNxM1U2bDdoT2Y2aVlvSGZoVGg0Zmp4NUxyMDhGOE9VS2NWTXQ4R2RO?= =?utf-8?B?RTZKdDVTejEraTUvTVg2cUh2NFJjNk1hZTRTMlpwVk1xalZnQVBnbUFGWDJ0?= =?utf-8?Q?4uFk=3D?= X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(36860700013)(1800799024)(376014)(7416014)(82310400026)(7053199007);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Nov 2025 16:09:10.1787 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 86550045-381e-4bd1-3013-08de1d4ed213 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: CH2PEPF0000009E.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR12MB7660 On 01-11-2025 05:32, Jim Mattson wrote: > With the VMCB's LBR_VIRTUALIZATION_ENABLE bit set, the CPU will load > the DebugCtl MSR from the VMCB's DBGCTL field at VMRUN. To ensure that > it does not load a stale cached value, clear the VMCB's LBR clean bit > when L1 is running and bit 0 (LBR) of the DBGCTL field is changed from > 0 to 1. (Note that this is already handled correctly when L2 is > running.) > > There is no need to clear the clean bit in the other direction, > because when the VMCB's DBGCTL.LBR is 0, the VMCB's > LBR_VIRTUALIZATION_ENABLE bit will be clear, and the CPU will not > consult the VMCB's DBGCTL field at VMRUN. > > Fixes: 1d5a1b5860ed ("KVM: x86: nSVM: correctly virtualize LBR msrs when L2 is running") > Reported-by: Matteo Rizzo > Reported-by: evn@google.com > Signed-off-by: Jim Mattson > --- > arch/x86/kvm/svm/svm.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index 153c12dbf3eb..b4e5a0684f57 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -816,6 +816,8 @@ void svm_enable_lbrv(struct kvm_vcpu *vcpu) > /* Move the LBR msrs to the vmcb02 so that the guest can see them. */ > if (is_guest_mode(vcpu)) > svm_copy_lbrs(svm->vmcb, svm->vmcb01.ptr); > + else > + vmcb_mark_dirty(svm->vmcb, VMCB_LBR); > } > > static void svm_disable_lbrv(struct kvm_vcpu *vcpu) Hi Jim, I am thinking, is it possible to add a test in KVM Unit Tests that covers this? Something where the stale cached value is loaded instead of the correct one, without your patch. Best regards, Shivansh