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Fri, 20 Jun 2025 23:10:20 +0000 Message-ID: Date: Fri, 20 Jun 2025 16:10:17 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv6 01/16] x86/cpu: Enumerate the LASS feature bits Content-Language: en-US To: Dave Hansen , "Kirill A. Shutemov" , Dave Hansen CC: Jonathan Corbet , Ingo Molnar , "Pawan Gupta" , Daniel Sneddon , Kai Huang , "Sandipan Das" , Breno Leitao , Rick Edgecombe , Alexei Starovoitov , Hou Tao , Juergen Gross , Vegard Nossum , Kees Cook , Eric Biggers , Jason Gunthorpe , "Masami Hiramatsu (Google)" , Andrew Morton , Luis Chamberlain , Yuntao Wang , "Rasmus Villemoes" , Christophe Leroy , Tejun Heo , Changbin Du , Huang Shijie , "Geert Uytterhoeven" , Namhyung Kim , Arnaldo Carvalho de Melo , , , , , Yian Chen , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , , "H. Peter Anvin" , Peter Zijlstra , "Ard Biesheuvel" , "Paul E. McKenney" , "Josh Poimboeuf" , Xiongwei Song , Xin Li , "Mike Rapoport (IBM)" , "Brijesh Singh" , Michael Roth , Tony Luck , Alexey Kardashevskiy , Alexander Shishkin References: <20250620135325.3300848-1-kirill.shutemov@linux.intel.com> <20250620135325.3300848-2-kirill.shutemov@linux.intel.com> <248e272c-79ec-4c11-a3a8-dff1de2147c0@intel.com> From: Sohil Mehta In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0334.namprd04.prod.outlook.com (2603:10b6:303:8a::9) To BYAPR11MB3320.namprd11.prod.outlook.com (2603:10b6:a03:18::25) Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR11MB3320:EE_|SA1PR11MB8319:EE_ X-MS-Office365-Filtering-Correlation-Id: de4fb062-f5ea-406d-85a1-08ddb04fa0e7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|366016; 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But, the difference in usage between both of them seems very >> subtle. Could this be easily misused? > > Logically there are two completely different things: > > 1. Touching userspace > 2. Touching the lower half of the address space > > If it's only userspace in the lower half of the address space, then > there's no controversy. But the problem obviously occurs when you want > to touch kernel mappings in the lower half of the address space. > Makes sense. If we decide to go this way, we should capture some of this thinking into the kernel comments. I find the current wording very ambiguous. > I want to preserve the "stac/clas" meaning as just "touch userspace". > > The new functions should be for "touch the lower half of the address > space" alone. Maybe it should be: > > lass_disable_enforcement() > lass_enable_enforcement() > > The only downside of not having stac/clac in the names is that it's not > obvious that they have an impact on SMAP because they're named to be > LASS-only. Yeah, the reverse is also true, where the SMAP specific clac()/stac() toggle LASS enforcement :)