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Dadhania" Subject: Re: [PATCH 0/2] KVM: kvm-coco-queue: Support protected TSC To: Marcelo Tosatti Cc: Isaku Yamahata , kvm@vger.kernel.org, pbonzini@redhat.com, Sean Christopherson , chao.gao@intel.com, rick.p.edgecombe@intel.com, yan.y.zhao@intel.com, linux-kernel@vger.kernel.org, isaku.yamahata@gmail.com, Tom Lendacky References: In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: PN0PR01CA0023.INDPRD01.PROD.OUTLOOK.COM (2603:1096:c01:4e::18) To DS7PR12MB6309.namprd12.prod.outlook.com (2603:10b6:8:96::19) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB6309:EE_|PH8PR12MB6747:EE_ X-MS-Office365-Filtering-Correlation-Id: 28e81521-8982-4a2d-72b4-08dcf74ed13c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014|7416014; X-Microsoft-Antispam-Message-Info: =?utf-8?B?T1VFVXQ4bjVWTVpEQ2prbXZwUzM5bjlISlhLUVIxVGVIbTE3bVhlY1JDU2I4?= =?utf-8?B?M3F5anlRaVNhZWlHVkdpTFY3L3dkUXlJa3dxcG5FUGFSaU05VXZiOU5nby9V?= =?utf-8?B?bUIvYmVUUGZyTHhYMjlFR2dYSlVpc1lVMWE5ZG00ZUZqZmZYVENNRnFXWElJ?= =?utf-8?B?MDBlQ2ZQRk9ZTzN6L1RmdGRmcmNOYUt0MEhWSHFuSFFIbm0xeHc3Y3hKUFZH?= =?utf-8?B?R3h6cmdtbTZ2WHJ4VHRoTU5XY2dVeVF2a3dqQThHRUtsYU9UVkl6b3FCdE9Y?= =?utf-8?B?dEM0NDRLcmNjaU5iMG5ENVZqV0hjZnFRYW1qb09VTzVIY1NnbUUwM2VYZ252?= =?utf-8?B?Q0xxVmZ1SWRWc0ErbnlKZjk4ZUdab2xFMFhpazlrMGZDaEJnU1JtOUVCb2Vl?= =?utf-8?B?aVlCZWd0QW81ODBjN2tyNlZ0Y2Q4WGlqMjFqL3p2M1M4clc4Qkp4emV5Smtt?= =?utf-8?B?MEd0RWdnK2tIeEx1eEZMcHVhOTcxbUZERlVwVkcwOWtDODFMTnVnbDkwZlo3?= =?utf-8?B?a0NUaU5pSzI1akgzVjl2UGxHZnRrZExVNUFNeGhYYVJGa21JSElWTHp6UEZ1?= =?utf-8?B?bnNiTUpJRXM5cnRoU09XZm52TmFuaURZbzhkZ0hFR3BBYTROcDNMZXQ1eGNM?= =?utf-8?B?bXErL1djaVYwM2g1M1ZGT004Zjc5M2xscExocEdsRlNCNHNTYW5qNTBTZUNJ?= =?utf-8?B?OFp6VTQ2cTZtaHUrU2w4cWw4SURZUENOL2JjOTdrcE5hWVFzRFgrMmhTNEFF?= =?utf-8?B?VjFXeUVLZWhxUUFhLysrYWRWU2pNYmJYRWlaVUhoYTlNVlZRTU14ZkZUaEpP?= =?utf-8?B?ZG8xOXJvUUhEQjRLcGhaOGkxeWQvQ0c3UU91ejlIcTdFTCtZeEFRVUswYks0?= =?utf-8?B?NEUxVDRUZ2hSbkNGSlZ6bkN4MjBhcDRVN3BnZVlKb3B3Z3VlNGE3M09lV0Qx?= =?utf-8?B?M04rYWpZbHRqWUo5VE5rbDRKSXpNZ2p5QU1OZ3NIMWdUT2drZGdDNmdNaG0v?= =?utf-8?B?WEdMdjVyRWYrSVIyejdFbmhTVkNyeXhYS2JFRmdRQjk3bUdORWlBYTdCdHkr?= =?utf-8?B?dXlJaThmS0prWE1SalBuWWNBaXEzVXowVTNaWUJVaWVBcXhKcDAwV0VrWFJS?= =?utf-8?B?Z1lSbmZDUjJ3K1RUVGhoRVJKN2c1OUxRZ0hlSWZUMTZQNzRoQ1N5VG90bzNu?= =?utf-8?B?T0llcTVXU3VLK1lybStocDdMeXNwTzFKMTZjMk1VV3RCWWdOakVPeHd1cmtM?= =?utf-8?B?UG8xbkVZbHJDQlVJcUdabjNiQSttSm1HdXlGa3o1azBFZmlRbmRBOGxGbERF?= =?utf-8?B?S0pmMHlUcmhralNtWDIyaytLbk94Nis2bTltTWREcDhrUklWdkp1TkZTL1Bs?= =?utf-8?B?VWZncUdLMkF3MjM5UndYT1VsS0JNM3BTeDZEQzBKU0JnUkxKZW1iU09OZGtN?= =?utf-8?B?azZyNzFGNHdLK2kwN0VGYTAzTWJYUUJ1SUk0ckpYczA5a3JBZXIxZ3ordGd0?= =?utf-8?B?Y3V4S0N4ZkMweEdGS1ZSL2NmU2dlV0xkQmUvekFKQ2tnWTlEbS81T3RzcFIz?= =?utf-8?B?RW1LendkTEluOXdTS3BaSzdvZVJXd3dEQzcxMVhtVUxPbHhLL2ZNV0lsdm44?= =?utf-8?B?SlR6YXp5YnFIcUQ2N3MwVENGdURwRjY1NXBrSmVKcXhNZEFnM2tPYTdqV1FQ?= =?utf-8?B?RUVVd2x0djVudUc3bm9NOG4yVzE3UlV0Q0lCMHlYU1hjY251YlNsMnZrTFpK?= =?utf-8?Q?SDPQB2UtPGm+HeF0/jLzZy4CumrwKnH0AMC/F06?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DS7PR12MB6309.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(366016)(1800799024)(376014)(7416014);DIR:OUT;SFP:1101; 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Dadhania wrote: >> On 10/12/2024 1:25 PM, Isaku Yamahata wrote: >>> Problem >>> ------- >>> The current x86 KVM implementation conflicts with protected TSC because the >>> VMM can't change the TSC offset/multiplier. Disable or ignore the KVM >>> logic to change/adjust the TSC offset/multiplier somehow. >>> >>> Because KVM emulates the TSC timer or the TSC deadline timer with the TSC >>> offset/multiplier, the TSC timer interrupts are injected to the guest at the >>> wrong time if the KVM TSC offset is different from what the TDX module >>> determined. >>> >>> Originally the issue was found by cyclic test of rt-test [1] as the latency in >>> TDX case is worse than VMX value + TDX SEAMCALL overhead. It turned out that >>> the KVM TSC offset is different from what the TDX module determines. >> >> Can you provide what is the exact command line to reproduce this problem ? > > Nikunj, > > Run cyclictest, on an isolated CPU, in a VM. For the maximum latency > metric, rather than 50us, one gets 500us at times. I tried out the cyclictest after referring to the documentation[1]. Here are the results of the run on an isolated CPU in the Secure TSC-enabled SEV-SNP VM (CPUs 16-31 are isolated in the VM): $ sudo taskset -c 16-31 ./cyclictest --mlockall --priority=80 --interval=200 --distance=0 -q -D 5m T: 0 ( 1226) P:80 I:200 C:1500000 Min: 6 Act: 10 Avg: 16 Max: 150 $ VM detail: 32 vCPUs VM, guest kernel v6.12-rc3 compiled with CONFIG_PREEMPT_RT=y > > FYI: > > SEV-SNP processors (at least the one below) do not seem affected by this problem. Thanks for testing on SEV-SNP. Regards, Nikunj 1. https://wiki.linuxfoundation.org/realtime/documentation/howto/tools/cyclictest/start