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Thu, 21 Aug 2025 19:34:05 +0000 Message-ID: <968a179f-3da7-4c69-b798-357ea8d759eb@intel.com> Date: Thu, 21 Aug 2025 12:34:01 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 13/15] x86/cpu/intel: Bound the non-architectural constant_tsc model checks To: David Woodhouse , , Dave Hansen , Tony Luck , =?UTF-8?Q?J=C3=BCrgen_Gross?= , Boris Ostrovsky , xen-devel CC: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , "Alexander Shishkin" , Jiri Olsa , Ian Rogers , Adrian Hunter , "Kan Liang" , Thomas Gleixner , Borislav Petkov , "H . Peter Anvin" , "Rafael J . Wysocki" , Len Brown , Andy Lutomirski , Viresh Kumar , Jean Delvare , Guenter Roeck , Zhang Rui , Andrew Cooper , "David Laight" , Dapeng Mi , , , , , , , Xin Li References: <20250219184133.816753-1-sohil.mehta@intel.com> <20250219184133.816753-14-sohil.mehta@intel.com> <6f05a6849fb7b22db35216dcf12bf537f8a43a92.camel@infradead.org> Content-Language: en-US From: Sohil Mehta In-Reply-To: <6f05a6849fb7b22db35216dcf12bf537f8a43a92.camel@infradead.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR03CA0340.namprd03.prod.outlook.com (2603:10b6:a03:39c::15) To DS0PR11MB7997.namprd11.prod.outlook.com (2603:10b6:8:125::14) Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB7997:EE_|SJ2PR11MB7575:EE_ X-MS-Office365-Filtering-Correlation-Id: 7b8f1f03-90c9-4c2d-9b8d-08dde0e9b08d X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|366016; 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My test host is INTEL_HASWELL_X (0x63f). For reasons which are > unclear to me, QEMU doesn't set bit 8 of 0x80000007 EDX unless I > explicitly append ',+invtsc' to the existing '-cpu host' on its command > line. So now my guest doesn't think it has X86_FEATURE_CONSTANT_TSC. > Haswell should have X86_FEATURE_CONSTANT_TSC, so I would have expected the guest bit to be set. Until now, X86_FEATURE_CONSTANT_TSC was set based on the Family-model instead of the CPUID enumeration which may have hid the issue. >From my initial look at the QEMU implementation, this seems intentional. QEMU considers Invariant TSC as un-migratable which prevents it from being exposed to migratable guests (default). target/i386/cpu.c: [FEAT_8000_0007_EDX] .unmigratable_flags = CPUID_APM_INVTSC, Can you please try '-cpu host,migratable=off'?