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Sat, 7 Feb 2026 00:37:29 +0000 Message-ID: Date: Fri, 6 Feb 2026 16:37:26 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] x86/x2apic: disable x2apic on resume if the kernel expects so Content-Language: en-US To: Shashank Balaji CC: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , , "H. Peter Anvin" , Suresh Siddha , "K. Y. Srinivasan" , "Haiyang Zhang" , Wei Liu , Dexuan Cui , Long Li , Ajay Kaher , Alexey Makhalov , Broadcom internal kernel review list , Jan Kiszka , Paolo Bonzini , Vitaly Kuznetsov , Juergen Gross , Boris Ostrovsky , Ingo Molnar , , , , , , , Rahul Bukte , Daniel Palmer , Tim Bird , References: <20260202-x2apic-fix-v1-0-71c8f488a88b@sony.com> <20260202-x2apic-fix-v1-1-71c8f488a88b@sony.com> <0149c37d-7065-4c72-ab56-4cea1a6c15d0@intel.com> <722b53a7-7560-4a1b-ab26-73eeed3dffa5@intel.com> From: Sohil Mehta In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR05CA0060.namprd05.prod.outlook.com (2603:10b6:a03:33f::35) To DS0PR11MB7997.namprd11.prod.outlook.com (2603:10b6:8:125::14) Precedence: bulk X-Mailing-List: linux-hyperv@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB7997:EE_|IA3PR11MB9376:EE_ X-MS-Office365-Filtering-Correlation-Id: 102c622a-490f-4cd8-9e31-08de65e112ec 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|7416014|376014; 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So it did what the setting says >>> >> I still think the firmware behavior is flawed. Some confusion originates from the option "Enable x2apic". Based on just these two words, the behavior seems highly ambiguous. I interpret it to mean "Make the x2apic feature available to the kernel". Then it is up to the kernel whether it decides to use it. If the intention of the BIOS option is to automatically/always enable x2apic then there is an architectural way to do it. It can set the bits that track to x2apic_hw_locked(). But, doing it this way during resume (behind OS's back) is unexpected. >> >> pr_warn_once("x2apic unexpectedly re-enabled by the firmware during >> resume.\n"); > > At least as per the spec, it's not something the firmware needs to fix, > and it's not unexpected re-enablement. > > Am I missing something? > > But it _is_ surprising that this bug went unnoticed for so long :) Maybe this BIOS option isn't typically found in a production firmware. I think it would be preferable to have the pr_warn_once() but I won't push super hard for it due to the unclear information. Whatever you choose for v2, can you please briefly describe the ambiguity in the commit message? It would help other reviewers provide better insight and be handy if we ever need to come back to this.