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Tue, 18 Aug 2026 00:58:15 +0000 Message-ID: Date: Mon, 17 Aug 2026 17:58:13 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 08/17] x86/resctrl: Enforce system RMID limit on AET event groups To: Tony Luck , Fenghua Yu , "Maciej Wieczor-Retman" , Peter Newman , James Morse , Babu Moger , Drew Fustini , Dave Martin , Chen Yu , David E Box , CC: Christoph Hellwig , , References: <20260729172752.11561-1-tony.luck@intel.com> <20260729172752.11561-9-tony.luck@intel.com> From: Reinette Chatre Content-Language: en-US In-Reply-To: <20260729172752.11561-9-tony.luck@intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0386.namprd04.prod.outlook.com (2603:10b6:303:81::31) To SJ2PR11MB8370.namprd11.prod.outlook.com (2603:10b6:a03:540::20) 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: SJ2PR11MB8370:EE_|SA7PR11MB9544:EE_ X-MS-Office365-Filtering-Correlation-Id: b1848a2d-95c6-4aa9-6609-08defcc3c8f9 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|366016|1800799024|7416014|23010399003|921020|6133799003|18002099003|22082099003|4143699003|11063799006|5023799004|56012099006|10067099003; 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But that number may be lower than the number supported > by the system. Especially true on systems with SNC (Sub-NUMA Cluster) > enabled as that reduces the number of supported RMIDs. > > Fix get_rdt_mon_resources() to return true when any monitor resource is hmmm ... "Fix" makes one look for the accompanying "Fixes:" tag. What is the fix here? What is wrong with existing implementation that needs fixing? To me this does not look like a fix though (more below). > possibly enabled. Call intel_aet_init() to adjust the event_group::num_rmid > values to not exceed the system supported maximum. Last sentence just documents the code. Please describe why this is needed. Is this a separate logical change? > > Signed-off-by: Tony Luck > --- ... > diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c > index 092764cf693f..2c938b97b147 100644 > --- a/arch/x86/kernel/cpu/resctrl/core.c > +++ b/arch/x86/kernel/cpu/resctrl/core.c > @@ -1019,10 +1019,10 @@ static __init bool get_rdt_mon_resources(void) > if (rdt_cpu_has(X86_FEATURE_ABMC)) > ret = true; > > - if (!ret) > - return false; > + if (ret) > + rdt_get_l3_mon_config(r); > > - return !rdt_get_l3_mon_config(r); > + return boot_cpu_data.x86_cache_max_rmid > 0; > } >From what I can tell this will return true when the system supports monitoring, but no resource may actually have monitoring enabled at this point. Specifically, no resource has rdt_resource::mon_capable set. The resctrl initialization now proceeds where it used to stop. resctrl_arch_late_init() will proceed and initialize the resctrl filesystem, which in turn would allow user space to mount it. rdt_get_tree() handling the user mount request could thus be run on a system that does not have a monitoring or allocation capable resource and then we see in rdt_get_tree(): if (resctrl_arch_alloc_capable() || resctrl_arch_mon_capable()) resctrl_mounted = true; The above flow change would cause resctrl to think the system supports monitoring but resctrl_arch_mon_capable() returns false. If there are no allocation features then this will result in resctrl fs mounted ... but resctrl_mounted is not set to true and thus allow a remount that is not supported. Reinette