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Fri, 25 Aug 2023 00:29:54 +0000 Received: from SJ2PR11MB7573.namprd11.prod.outlook.com ([fe80::47e:3e1f:bef4:20e0]) by SJ2PR11MB7573.namprd11.prod.outlook.com ([fe80::47e:3e1f:bef4:20e0%3]) with mapi id 15.20.6699.027; Fri, 25 Aug 2023 00:29:54 +0000 Message-ID: <837b1558-1ac9-d05d-e8f2-90d33e259326@intel.com> Date: Thu, 24 Aug 2023 17:29:39 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Firefox/102.0 Thunderbird/102.14.0 Subject: Re: [PATCH v5 02/24] x86/resctrl: Access per-rmid structures by index Content-Language: en-US To: James Morse , , CC: Fenghua Yu , Thomas Gleixner , Ingo Molnar , Borislav Petkov , H Peter Anvin , Babu Moger , , D Scott Phillips OS , , , , , , , Jamie Iles , Xin Hao , , References: <20230728164254.27562-1-james.morse@arm.com> <20230728164254.27562-3-james.morse@arm.com> From: Reinette Chatre In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0384.namprd04.prod.outlook.com (2603:10b6:303:81::29) To SJ2PR11MB7573.namprd11.prod.outlook.com (2603:10b6:a03:4d2::10) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ2PR11MB7573:EE_|SJ0PR11MB4928:EE_ X-MS-Office365-Filtering-Correlation-Id: 2f4dfa23-9829-4f1b-58b2-08dba50266f0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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>>> struct rmid_entry *entry; >>> >>> - if (!rmid) >>> - return; >>> - >>> lockdep_assert_held(&rdtgroup_mutex); >>> >>> - entry = __rmid_entry(closid, rmid); >>> + /* do not allow the default rmid to be free'd */ >>> + if (idx == resctrl_arch_rmid_idx_encode(RESCTRL_RESERVED_CLOSID, >>> + RESCTRL_RESERVED_RMID)) >>> + return; >>> + > >> Why is this encoding necessary? Can the provided function parameters >> not be tested directly against RESCTRL_RESERVED_CLOSID and >> RESCTRL_RESERVED_RMID ? > > Doing this by encoding means if the architecture code supplies an > resctrl_arch_rmid_idx_encode() that ignores the closid, this reduces down to: > | if (rmid == RESCTRL_RESERVED_RMID) > > which is what the code did before. I'll add a comment: > | /* > | * Do not allow RESCTRL_RESERVED_RMID to be free'd. Comparing by index > | * allows architectures that ignore the closid parameter to avoid an > | * unnecessary check. > | */ > Sounds good. Thank you. Reinette