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Mon, 16 Mar 2026 17:29:43 +0000 Message-ID: Date: Mon, 16 Mar 2026 10:29:04 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/6] fs/resctrl: Make 'event_filter' files read only if they're not configurable To: Ben Horgan , "Luck, Tony" CC: "linux-kernel@vger.kernel.org" , "Dave.Martin@arm.com" , "james.morse@arm.com" , "babu.moger@amd.com" , "tglx@kernel.org" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "fenghuay@nvidia.com" , "tan.shaopeng@fujitsu.com" References: <20260313174524.3482767-1-ben.horgan@arm.com> <20260313174524.3482767-4-ben.horgan@arm.com> <359217bc-59d1-4abf-89b1-77f5821b2a6f@arm.com> From: Reinette Chatre Content-Language: en-US In-Reply-To: <359217bc-59d1-4abf-89b1-77f5821b2a6f@arm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY3PR10CA0009.namprd10.prod.outlook.com (2603:10b6:a03:255::14) To SN7PR11MB7566.namprd11.prod.outlook.com (2603:10b6:806:34d::7) 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: SN7PR11MB7566:EE_|MN2PR11MB4743:EE_ X-MS-Office365-Filtering-Correlation-Id: bb40472a-e763-4947-ab22-08de83819c82 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|366016|18002099003|22082099003|56012099003; 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Maybe >>>> patch the mode in res_common_files[] before calling rdtgroup_add_files(): >>> >>> >>> I initially rejected this idea because res_common_files[] is global and the >>> read/write choice is per event type but we can safely save restore the mode as >>> we're holding the rdtgroup mutex. How about this? >> >> That seems more complicated. Is there an expectation that event_filter >> needs to be writable on the "total" event but not on the "local" one? > > No, at least not currently. For mpam only the total event is supported. > > Another way of doing it could be to patch the mode in res_common_files[] from > resctrl_mkdir_event_configs() for both cases, 0444 and 0644, and change the > starting value to something invalid, e.g. 0. "event_filter"'s mode could be initialized similar to its fflags. Please see resctrl_l3_mon_resource_init(). Stepping back, based on the v1 discussion I understand that BMEC does not apply to MPAM so patching the BMEC specific resctrl_arch_is_evt_configurable() in patch #1 to support MPAM does not look right. From what I can tell we need a new "configurable" property that is specific to assignable counters. I understand naming is not ideal here but forcing the two independent features together like this just because resctrl_arch_is_evt_configurable() has a generically relevant name is not right. Consider, for example, a new rdt_resource::resctrl_mon::mbm_cntr_configurable property that arch can set. From resctrl fs side it would be a property that is only considered if rdt_resource::resctrl_mon::mbm_cntr_assignable == true. res_common_files[] can initialize the default mode of "event_filter" to be read-only and resctrl_l3_mon_resource_init() can be expanded to to make "event_filter" writable if both rdt_resource::resctrl_mon::mbm_cntr_assignable == true AND rdt_resource::resctrl_mon::mbm_cntr_configurable == true. Looking at this we do seem to have options between resctrl fs properties and arch callbacks to do this and considering your earlier concern with callbacks I wonder if resctrl fs properties would be better? How about another new property, rdt_resource::resctrl_mon::mbm_cntr_assign_fixed to replace resctrl_arch_mbm_cntr_assign_fixed()? Reinette