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Thu, 19 Feb 2026 21:02:46 +0000 Message-ID: Date: Thu, 19 Feb 2026 13:02:43 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/3] x86/cpu: Defer LASS enabling until userspace comes up Content-Language: en-US To: , Dave Hansen , "Thomas Gleixner" , Ingo Molnar , "Borislav Petkov" , Ard Biesheuvel , "Nikunj A. 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Shutemov" , Rick Edgecombe , Andrew Cooper , Tony Luck , "Alexander Shishkin" , , References: <20260120234730.2215498-1-sohil.mehta@intel.com> <20260120234730.2215498-2-sohil.mehta@intel.com> From: Sohil Mehta In-Reply-To: <20260120234730.2215498-2-sohil.mehta@intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR13CA0229.namprd13.prod.outlook.com (2603:10b6:a03:2c1::24) To DS0PR11MB7997.namprd11.prod.outlook.com (2603:10b6:8:125::14) Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB7997:EE_|CH3PR11MB8095:EE_ X-MS-Office365-Filtering-Correlation-Id: 811f9dd7-f870-425e-d3f4-08de6ffa3b5d 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|366016|376014|7416014; X-Microsoft-Antispam-Message-Info: =?utf-8?B?VE9kMERSZ1J6NDZhOHhiTDVPSGVpcXdYMHI0MUNLQXl6QTBIa0VRbWNCMkR4?= =?utf-8?B?VGdKTDlIdms0UDcvQUFyU01MS3M3Zkx6alBzUGc1R2N6amJ1TVZpVjcyb3ZN?= =?utf-8?B?cHBXUS96U1AxZW83T2F2VG5Ja0VUbWxXMnQrdkpKYW42VkVzc010NkdEZmZ4?= =?utf-8?B?bXlQazY3MUVPaXlUZERJWnZCSlNURkRaUlpTbm96TFhkY05CTE0zYzNFOU5o?= =?utf-8?B?aGdMLysveWYwMExMTVpWMXRqZDJUMVlkeHFoeTNSVXZtR2g4d0xtaUJVRFJV?= =?utf-8?B?UURmZEplUTRFc1UxdmI5SFNOUEcrSmVJdDZoanpFd1RZRG1GZGRTczd6SklI?= =?utf-8?B?OGtyR1BBSUJQR3B2U0szd21RaTVTam1ERStJajdGNkw5RjFZN2pGeklpV1F5?= =?utf-8?B?MVlVenY0bjFtbUk4QVpkV3QwMEswVWVXNzB4ajBYV0kwZmVYVFpOa28zZFNk?= =?utf-8?B?dFR6Sm42V1lPbkh2QkEzK2xldTkrVDZ4MG9VV2MvWjNjVFRYYmczdS9JWHly?= =?utf-8?B?NEpqclp3Um1zdzlGZnBOSnBFU2g1KzJUWE04OFdtbGdnRTd2eWFhaFJvVHBN?= =?utf-8?B?L3RFdFd5bk9jZkRsVzdCemdsK3ZrZVFTYnpucWZEOUEvUXpMRDNJeU9GaWRj?= =?utf-8?B?c3dDc2ViQkdQRFZZaVMzSWlSeVRzY3lsZFRKSFhqeUdjMzZGWDIwUzIwOUIx?= =?utf-8?B?R1ZHc0dEcWJVeU1WODZ5QVljMkJyaUJLdGxBdnBGM2pDck1pVFBheEtleVZ6?= =?utf-8?B?YjU3UVFrVUluVWx6RXJNWjl2WWJnQndUTkpFMXVneFlBUU9ZMkxicFQ1R2hF?= =?utf-8?B?aFdEL3g2d2h4dlB6eERPdkdnV055eHplTDhiRWZUT3VjWWhmUnlPakxBOUUy?= =?utf-8?B?eGRsWEFGdTNEazNRajJhajRYaFdhRTZub3lMMmNlOFdkSlJXZzRKR05hYWsy?= =?utf-8?B?K1d5TTV2QjFQbjVZR05wbnFpK0xoOUQ1N0NzSzRURS8zMHlqdGZZSXFoRGpN?= =?utf-8?B?clBiRm1DL01zUnR4ZzQ3WFY1UjZ6WlFINU5OcmgvMmxmb3VvWXI5MWJ0WkYw?= =?utf-8?B?c3UxeXVHV0NHTCt6QlFzc1FuQm5ad21tUjBqbnlQbFNOdHdabTk0dlpNMXRj?= =?utf-8?B?cGVybXcwbzNmSGhaelFaSmNxbm96cjZUVmUrTVZBbURLRC9FYzdNQlFsL0xC?= =?utf-8?B?VVAvMzY4WG1zWnRQWjZ0NDZpbEVlZnhqeFBseGtYVGhyZ25zOUhOR0Z3Q2Vx?= =?utf-8?B?QVZ2MlQrTkZMUFVWcHlOU0p5VmltY1MzZDFWSzJWMEEwbUpLeVo3NTI0NFBJ?= =?utf-8?B?WUtaTzhKQ2MyM3hSR3NmZzEyYTQ0VldENDVIZkhyNDl5M3g5dTZ0ZDVpR3Uz?= =?utf-8?B?RHhwWnBuMkhtUkVYRGdDVU5rM2FleTNvTjRoemlDdDYyZkc3MjRFNVRHandW?= =?utf-8?B?bEdmb2Vhdm1CUkphZmMva3hMZWRCVlNJM0RONVRxV3l1c2pIR1BUUGRldWZG?= =?utf-8?B?UzJhalhPZGdaOHdzTXFyMmJsVnpSenZmRk9lUWV6SkxNSmdpbGZoY3VOL1l3?= =?utf-8?B?cHNOYXhNSXJIcmp3Q04vRmNTMTllb2hucEtVTWZPYXhucjAzQ1pTcDR1R0VZ?= =?utf-8?B?OFNMNlRqWGUwQmhrTk8wRWVzN1FZVm9GaWZhMktOVkQzWkdIYnZEaklHYnZR?= =?utf-8?B?bUVuVmNpOFN0RTZaT1R6TnFpR2JMNnNldXQ4K0VneEVsZDJycGpCKzVaZCtX?= =?utf-8?B?MVF0NjBRZUEyTlFDNHluRkk2bG92YTlRQ3hsQ0ttK0lkTjNpQlNybEV1b1dj?= =?utf-8?B?aW8wNllocmRTWFlDUFFvakpldlhKZlFUTjBWdTlkQkVXQzZlR0JXclMxZyty?= =?utf-8?B?d0xuTGVHT0VzbXBkN1orNDMzb0RrVXpmVVlGdDIzTDRiTW5hb3dhWGEwMW9J?= =?utf-8?B?WVNYMEE4dTFFUHNLcUZIOEd5VllWYVpjbFNEbUprNnpuc2NIQmcyR3IyT2Zt?= =?utf-8?B?N2pRemhtT2hJYW5DY21sZ1lORGZZbi9TMTJ5ZGZGY0w0Ly90UHo4OHp6N090?= =?utf-8?B?bzVlUDIrTTNQb0hxYTg0YytQeUxndzk3TFdiS1NqS3puN04zRHhaUkNoSEdK?= =?utf-8?Q?cyg4=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DS0PR11MB7997.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(366016)(376014)(7416014);DIR:OUT;SFP:1101; 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Note that this only runs on a single CPU. Use appropriate > + * callbacks if all the CPUs need to reflect the same change. > + */ > +static int cpu_finalize_pre_userspace(void) > +{ > + if (!cpu_feature_enabled(X86_FEATURE_LASS)) > + return 0; > + > + /* Runs on all online CPUs and future CPUs that come online. */ > + cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/lass:enable", enable_lass, NULL); > + > + return 0; > +} > +late_initcall(cpu_finalize_pre_userspace); > + @Dave, Nikunj, The current patch https://lore.kernel.org/lkml/1bc0b798-9cef-4dfd-af06-7674b699af1b@intel.com/ ..to defer CR pinning enforcement until CPU online makes sense for the FRED fix. Eventually, I am thinking we can defer CR pinning even further until userspace comes up. setup_cr_pinning(), which enables the static key, can be moved to a late_initcall() such as above. The cpu_online() check to enforce CR pinning would still be needed to make it play nice with CPU hotplug. Do you see an issue with that approach? > /* These bits should not change their value after CPU init is finished. */ > static const unsigned long cr4_pinned_mask = X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP | > X86_CR4_FSGSBASE | X86_CR4_CET | X86_CR4_FRED;