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Tue, 22 Jul 2025 21:16:38 +0000 Message-ID: <2249977a-e291-494f-8c84-f16ec9fba10b@intel.com> Date: Tue, 22 Jul 2025 14:16:35 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86/resctrl: avoid divide by 0 num_rmid To: Barret Rhoden CC: Tony Luck , Dave Martin , "James Morse" , , "x86@kernel.org" References: <20250721180051.3645697-1-brho@google.com> From: Reinette Chatre Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MW4PR04CA0125.namprd04.prod.outlook.com (2603:10b6:303:84::10) 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_|DS0PR11MB7735:EE_ X-MS-Office365-Filtering-Correlation-Id: ca3df044-8f40-4c57-8881-08ddc9650b5c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|366016|7053199007; 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Specifically: >> >> resctrl_cpu_detect(): >>     if (!cpu_has(c, X86_FEATURE_CQM_LLC)) { >>         c->x86_cache_max_rmid  = -1; >>         ... >>     } >> >> The function modified by this patch, rdt_get_mon_l3_config() only runs if >> the hardware supports one or more of the L3 monitoring sub-features >> (X86_FEATURE_CQM_OCCUP_LLC, X86_FEATURE_CQM_MBM_TOTAL, or >> X86_FEATURE_CQM_MBM_LOCAL) that depend on X86_FEATURE_CQM_LLC per cpuid_deps[]. >> >> I tried to reproduce the issue on real hardware by using clearcpuid to >> disable X86_FEATURE_CQM_LLC and the CPUID dependencies did the right thing >> by automatically disabling X86_FEATURE_CQM_OCCUP_LLC, X86_FEATURE_CQM_MBM_TOTAL, >> X86_FEATURE_CQM_MBM_LOCAL, not running rdt_get_mon_l3_config() at all, and >> not even attempt to enumerate any of the L3 monitoring details. >> >> What are the symptoms when you encounter this issue? > > Linux crashes during boot with a divide error, and the splat backtrace is in rdt_get_mon_l3_config(). > >> Would it be possible to send me the CPUID flags of leaf 7, subleaf 0 as >> well as all sub-leaves of leaf 0xF? > > # ./cpuid 0x7 0 > CPUID for Leaf 0x00000007, Sublevel 0x00000000: >     eax: 00000002 >     ebx: f1bf2ffb Looks like X86_FEATURE_CQM_LLC is off. >     ecx: 1b415f7e >     edx: bc814410 > > # ./cpuid 0x7 1 > CPUID for Leaf 0x00000007, Sublevel 0x00000001: >     eax: 00201c30 >     ebx: 00000000 >     ecx: 00000000 >     edx: 00084000 > > # ./cpuid 0x7 2 > CPUID for Leaf 0x00000007, Sublevel 0x00000002: >     eax: 00000000 >     ebx: 00000000 >     ecx: 00000000 >     edx: 0000003f > Thank you. Could you please also pass on all sub-leaves of leaf 0xF? Thank you very much. Reinette