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Fri, 13 Mar 2026 18:05:12 +0000 Message-ID: Date: Fri, 13 Mar 2026 11:05:10 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] x86/cpu: Disable CR pinning during CPU bringup Content-Language: en-US To: "Nikunj A. Dadhania" , Dave Hansen , Tom Lendacky , "Borislav Petkov" CC: , , , , , , , , , , References: <20260226092349.803491-1-nikunj@amd.com> <20260226092349.803491-2-nikunj@amd.com> <20260309134640.GOaa7PQJli_C9QATGB@fat_crate.local> <20260309161516.GAaa7yFMulhdzNQ-pt@fat_crate.local> <70644e1d-dd0e-4f0f-81c0-fd095e46e50b@intel.com> <7ca205d6-b01b-4ed3-959d-db31a6496d79@amd.com> <505a6bbd-3ecf-4de9-8fb9-0b21c3435a96@intel.com> <9fa61b80-0e16-4a87-a0e7-3c3dfcda8f7e@amd.com> <55a98b6d-e831-47a6-aa5a-8fe357334f67@intel.com> <13f67190-b51c-4719-a409-13d813549d7c@intel.com> <1439b4f4-ff0c-4b6a-ac86-5c0da2d26cf5@amd.com> From: Sohil Mehta In-Reply-To: <1439b4f4-ff0c-4b6a-ac86-5c0da2d26cf5@amd.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR01CA0057.prod.exchangelabs.com (2603:10b6:a03:94::34) To DS0PR11MB7997.namprd11.prod.outlook.com (2603:10b6:8:125::14) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB7997:EE_|SJ0PR11MB5917:EE_ X-MS-Office365-Filtering-Correlation-Id: 95a3f109-2864-42e8-8a05-08de812b126f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|366016|1800799024|18002099003|22082099003|56012099003; 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Dadhania wrote: > @@ -2413,6 +2407,16 @@ void cpu_init_exception_handling(bool boot_cpu) > /* GHCB needs to be setup to handle #VC. */ > setup_ghcb(); > > + /* > + * CPUs that support FSGSBASE may use RDGSBASE/WRGSBASE in > + * paranoid_entry(). Enable the feature before any exceptions > + * occur. > + */ > + if (cpu_feature_enabled(X86_FEATURE_FSGSBASE)) { > + cr4_set_bits(X86_CR4_FSGSBASE); > + elf_hwcap2 |= HWCAP2_FSGSBASE; > + } > + There is already a lot happening in this function. If we end up going this route, I would suggest moving this to a small wrapper function such as setup_fsgsbase() or enable_fsgsbase(). cpu_init_exception_handling() doesn't seem to be in a hot-path and cpu_feature_enabled(X86_FEATURE_FSGSBASE) is generally expected to be true on modern CPUs. > if (cpu_feature_enabled(X86_FEATURE_FRED)) { > /* The boot CPU has enabled FRED during early boot */ > if (!boot_cpu) > > Regards, > Nikunj > >