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Fri, 13 Feb 2026 00:14:10 +0000 Message-ID: <57039edb-419c-4e4a-96d0-3578e233b594@intel.com> Date: Thu, 12 Feb 2026 16:14:07 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 1/3] x86/cpu: Clear feature bits disabled at compile-time Content-Language: en-US To: Borislav Petkov CC: "H. Peter Anvin" , Maciej Wieczor-Retman , Dave Hansen , "Thomas Gleixner" , Ingo Molnar , , , Farrah Chen , Maciej Wieczor-Retman , , References: <32fbbfc16974cfed11e7d2651bce836ba9ceaccc.1770908783.git.m.wieczorretman@pm.me> <20260212155808.GDaY34kOTrEYHLdoyK@fat_crate.local> <19d3f1c8-01aa-4a50-81e0-6af3fb7fe9cd@intel.com> <20260212234722.GFaY5mimfap5YbOi30@fat_crate.local> From: Sohil Mehta In-Reply-To: <20260212234722.GFaY5mimfap5YbOi30@fat_crate.local> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY5PR20CA0021.namprd20.prod.outlook.com (2603:10b6:a03:1f4::34) 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_|IA3PR11MB8985:EE_ X-MS-Office365-Filtering-Correlation-Id: 6073ca0e-4edc-4ecd-29fa-08de6a94cf37 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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As described below, it has been buggy for *some* features for a long time. >> We have always said that the *absence* of the feature doesn't mean anything. >> The feature could be disabled or the kernel doesn't know about it. >> >> And now we've realized that the *presence* of the feature in /proc/cpuinfo >> doesn't mean anything either. > > How so? The presence means, the kernel has enabled it. See > Documentation/arch/x86/cpuinfo.rst > The commit message says: "The features are also visible in /proc/cpuinfo even though they are not enabled... Examples of such feature flags are lam, fred, sgx, ibrs_enhanced, split_lock_detect, user_shstk, avx_vnni and enqcmd." So, as of today, if one of these features shows up, a user can't be sure whether the kernel has enabled it or not. Right? My suggestion is that: Instead of (or maybe along with) fixing this buggy interface, would it be better to put this information in something like debugfs/sysfs? So, at least new user software can start using that.