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Wed, 22 Apr 2026 17:24:23 +0000 Message-ID: Date: Wed, 22 Apr 2026 10:24:19 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 1/3] x86/process: Shorten the LAM tag width To: Maciej Wieczor-Retman , , , , , , , , , , , , , , , , , , , , , , , CC: , , , References: <79720f2640839b15f22e3618136b084cb376456b.1775813245.git.m.wieczorretman@pm.me> Content-Language: en-US From: Sohil Mehta In-Reply-To: <79720f2640839b15f22e3618136b084cb376456b.1775813245.git.m.wieczorretman@pm.me> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR13CA0180.namprd13.prod.outlook.com (2603:10b6:a03:2c7::35) 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_|IA1PR11MB7941:EE_ X-MS-Office365-Filtering-Correlation-Id: 47f8c178-33e3-4f23-efff-08dea093fe99 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|366016|1800799024|376014|56012099003|18002099003|22082099003|921020; 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What we essentially need is 4 bits starting from bit 57. GENMASK is the right macro for that, but it doesn't need these extra argument macros and tail comments. I think using direct numbers with a simple comment on top would be better. How about something like? /* Must use the 4 lower bits from the LAM_U57 tag bits 62:57 */ #define LAM_UNTAG_MASK ~GENMASK(60, 57) You can probably add some explanation in the commit log about why only the lower bits can be used. > static void enable_lam_func(void *__mm) > { > @@ -814,7 +817,7 @@ static void enable_lam_func(void *__mm) > static void mm_enable_lam(struct mm_struct *mm) > { > mm->context.lam_cr3_mask = X86_CR3_LAM_U57; > - mm->context.untag_mask = ~GENMASK(62, 57); > + mm->context.untag_mask = LAM_UNTAG_MASK; > Other than that, Reviewed-by: Sohil Mehta