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Tue, 10 Feb 2026 00:18:35 +0000 Message-ID: <52e152b9-c840-4480-9337-0f0aca327543@intel.com> Date: Mon, 9 Feb 2026 16:18:32 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] x86/smp: Set up exception handling before cr4_init() From: Sohil Mehta To: Xin Li , Dave Hansen CC: , , , , , , , , , , , , References: <20260206185035.1250577-1-xin@zytor.com> <37de06e1-aae4-4ebd-ac93-1846ee4cd91e@intel.com> Content-Language: en-US In-Reply-To: <37de06e1-aae4-4ebd-ac93-1846ee4cd91e@intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR13CA0048.namprd13.prod.outlook.com (2603:10b6:a03:2c2::23) To DS0PR11MB7997.namprd11.prod.outlook.com (2603:10b6:8:125::14) 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: DS0PR11MB7997:EE_|CY5PR11MB6413:EE_ X-MS-Office365-Filtering-Correlation-Id: 4a82f369-2e3b-4181-38c5-08de6839ee1b 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|366016|7416014|376014|1800799024; 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I added a debug print in cpu_init_fred_exceptions() to test FRED behavior. if (cr4_read_shadow() & X86_CR4_FRED) pr_warn("FRED is already enabled on CPU%d\n", smp_processor_id()); With Dave's patch, the warning no longer shows up on APs. However, I found another location where we enable FRED in CR4 before enabling the MSRs. __restore_processor_state(): ... __write_cr4(ctxt->cr4); ... if (ctxt->cr4 & X86_CR4_FRED) { cpu_init_fred_exceptions(); cpu_init_fred_rsps(); } Due to limitations of my test platform, I couldn't verify the FRED print in __restore_processor_state()'s path. But, could "restore" run into a similar issue in the future?