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Wed, 30 Oct 2024 23:57:34 +0000 Message-ID: Date: Wed, 30 Oct 2024 16:57:33 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] x86/cpufeature: Add feature dependency checks To: "Luck, Tony" , "x86@kernel.org" , Borislav Petkov , Dave Hansen CC: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , Uros Bizjak , Sandipan Das , Sean Christopherson , "Peter Zijlstra" , Vegard Nossum , Pawan Gupta , Nikolay Borisov , Eric Biggers , "Li, Xin3" , "Shishkin, Alexander" , Kirill Shutemov , "linux-kernel@vger.kernel.org" References: <20241030233118.615493-1-sohil.mehta@intel.com> Content-Language: en-US From: Sohil Mehta In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY3PR05CA0025.namprd05.prod.outlook.com (2603:10b6:a03:254::30) To BYAPR11MB3320.namprd11.prod.outlook.com (2603:10b6:a03:18::25) 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: BYAPR11MB3320:EE_|PH0PR11MB5191:EE_ X-MS-Office365-Filtering-Correlation-Id: 3f0c977b-b0e9-44f6-6f59-08dcf93e9ff0 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|7416014|366016|376014; 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>> + >> + for (d = cpuid_deps; d->feature; d++) { >> + if (cpu_has(c, d->feature) && !cpu_has(c, d->depends)) >> + do_clear_cpu_cap(c, d->feature); >> + } >> +} > > The dependency check found something very wrong. Should there be > a pr_warn() to give some clue that Linux papered over this problem? > Not sure if this necessitates a warning. A missing feature may not be a problem for the user. I am treating a disabled feature due to the original CPUID enumeration not being present vs due to a dependency not being met as the same. System and kernel developers would definitely care if an expected feature is missing. Maybe a pr_debug()? Want to avoid unnecessary escalations and bug reports. Sohil