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Fri, 13 Mar 2026 18:33:34 +0000 Date: Fri, 13 Mar 2026 11:33:32 -0700 From: "Luck, Tony" To: Ben Horgan CC: , , , , , , , , , , , , Subject: Re: [PATCH v2 3/6] fs/resctrl: Make 'event_filter' files read only if they're not configurable Message-ID: References: <20260313174524.3482767-1-ben.horgan@arm.com> <20260313174524.3482767-4-ben.horgan@arm.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260313174524.3482767-4-ben.horgan@arm.com> X-ClientProxiedBy: BYAPR05CA0072.namprd05.prod.outlook.com (2603:10b6:a03:74::49) To DS7PR11MB6077.namprd11.prod.outlook.com (2603:10b6:8:87::16) 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: DS7PR11MB6077:EE_|CYXPR11MB8691:EE_ X-MS-Office365-Filtering-Correlation-Id: f403d7f8-c5d4-4769-6c3c-08de812f08cc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|366016|18002099003|56012099003|22082099003; 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These files > live at info/L3_MON/event_configs//event_filter and are used to > display and set the event configuration. The MPAM driver has no support for > changing event configuration and so mbm_event mode can't be used. > > In order to support mbm_event event with MPAM make the 'event_filter' files > read only if the event configuration can't be changed. A user can still > chmod the file and so also return an error from event_filter_write(). > +++ b/fs/resctrl/rdtgroup.c > @@ -2341,6 +2341,22 @@ static int resctrl_mkdir_event_configs(struct rdt_resource *r, struct kernfs_nod > ret = rdtgroup_add_files(kn_subdir2, RFTYPE_ASSIGN_CONFIG); > if (ret) > return ret; > + > + if (!resctrl_arch_is_evt_configurable(mevt->evtid, true)) { > + struct iattr iattr = {.ia_valid = ATTR_MODE,}; > + struct kernfs_node *kn; > + > + kn = kernfs_find_and_get_ns(kn_subdir2, "event_filter", NULL); > + if (!kn) > + return -ENOENT; > + > + iattr.ia_mode = S_IFREG | 0444; > + > + ret = kernfs_setattr(kn, &iattr); > + kernfs_put(kn); > + if (ret) > + return ret; > + } Instead of making the file writable, and then fixing the mode. Maybe patch the mode in res_common_files[] before calling rdtgroup_add_files(): if (!resctrl_arch_is_evt_configurable(mevt->evtid, true)) { struct rftype *rft; rft = rdtgroup_get_rftype_by_name("event_filter"); if (rft) rft->mode = 0444; } -Tony