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Mon, 9 Feb 2026 07:28:44 +0000 Message-ID: <37de06e1-aae4-4ebd-ac93-1846ee4cd91e@intel.com> Date: Sun, 8 Feb 2026 23:28:41 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] x86/smp: Set up exception handling before cr4_init() Content-Language: en-US To: Xin Li , Dave Hansen CC: , , , , , , , , , , , , References: <20260206185035.1250577-1-xin@zytor.com> From: Sohil Mehta In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SJ0PR05CA0093.namprd05.prod.outlook.com (2603:10b6:a03:334::8) 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_|SA1PR11MB8318:EE_ X-MS-Office365-Filtering-Correlation-Id: 3736c045-8a47-477a-0087-08de67acdb33 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|7416014|376014|366016|1800799024; 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IOW, > why does it need to be called so early in the existing code? > The name cpu_init() is misleading. Most of the pinned features don't get initialized in cpu_init(). They are set up slightly later: start_secondary() ap_starting() identify_secondary_cpu() identify_cpu() The original reason for writing CR4 early on APs probably originates in commit c7ad5ad297e6 ("x86/mm/64: Initialize CR4.PCIDE early"). Then, when CR pinning was introduced, it was a global system-wide concept. So, the pinned bits had to be programmed when the first write to CR4 happened. > >> >> I _really_ think we need a defined per-cpu point where pinning comes >> into effect. Marking the CPU online is one idea. >> >> Thoughts? > I think this approach could work. It should cover APs as well as hotplug CPUs that come online later. > It seems a good fit. Just that {on,off}line() are not called on BSP (not > a real problem). > The BSP is marked online in boot_cpu_init()->set_cpu_online(). So, it should be covered as well. > Question is that who would work on it ;) ? I think Dave already posted the patch for it here. https://lore.kernel.org/lkml/02df7890-83c2-4047-8c88-46fbc6e0a892@intel.com/ I will test that out to confirm that it doesn't mess up some implicit behavior.