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Thu, 24 Apr 2025 15:17:37 +0000 Message-ID: Date: Thu, 24 Apr 2025 08:17:34 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 02/21] x86/resctrl: Remove the limit on the number of CLOSID To: James Morse , , CC: Thomas Gleixner , Ingo Molnar , Borislav Petkov , H Peter Anvin , Babu Moger , , "D Scott Phillips OS" , , , , , , Jamie Iles , Xin Hao , , , , David Hildenbrand , Rex Nie , "Dave Martin" , Koba Ko , Shanker Donthineni , , Shaopeng Tan References: <20250411164229.23413-1-james.morse@arm.com> <20250411164229.23413-3-james.morse@arm.com> From: Reinette Chatre Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW2PR16CA0006.namprd16.prod.outlook.com (2603:10b6:907::19) To SJ2PR11MB7573.namprd11.prod.outlook.com (2603:10b6:a03:4d2::10) 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: SJ2PR11MB7573:EE_|SN7PR11MB7468:EE_ X-MS-Office365-Filtering-Correlation-Id: c6e2deb5-1452-4434-a72c-08dd83432538 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|366016|7416014|376014; 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There is at least one MPAM platform which >> supports more than 32 CLOSID values. >> >> Replace the fixed size bitmap with calls to the bitmap API to allocate >> an array of a sufficient size. >> >> ffs() returns '1' for bit 0, hence the existing code subtracts 1 from >> the index to get the CLOSID value. find_first_bit() returns the bit >> number which does not need adjusting. > >> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> index 776c8e347654..4e0308040c6e 100644 >> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c > >> @@ -152,20 +152,31 @@ int closids_supported(void) >> return closid_free_map_len; >> } >> >> -static void closid_init(void) >> +static int closid_init(void) >> { >> struct resctrl_schema *s; >> - u32 rdt_min_closid = 32; >> + u32 rdt_min_closid = ~0; >> >> /* Compute rdt_min_closid across all resources */ >> list_for_each_entry(s, &resctrl_schema_all, list) >> rdt_min_closid = min(rdt_min_closid, s->num_closid); > > Platforms that don't have any controls - only monitors - will still call closid_init(). > Previously this initialised the fixed-sized bitmap, which was harmless as helpers like > closid_alloc() are never called. > > With this change, rdt_min_closid keeps its dummy initialisation value of ~0, meaning this: > >> - closid_free_map = BIT_MASK(rdt_min_closid) - 1; >> + closid_free_map = bitmap_alloc(rdt_min_closid, GFP_KERNEL); > > Blows up with a greater than 'max order' error. > > I've added a list_empty() check to the top of the function: > | /* Monitor only platforms still call closid_init() */ > | if (list_empty(&resctrl_schema_all)) > | return 0; > > (list-empty as its clearer what goes wrong without the check). > I reckon this is minor, so I'll keep the existing tags. > > > I'm not aware of anyone building a monitor-only MPAM platform - I configured one by > accident with one of the software models! > Thank you very much for catching this. Reinette