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Thu, 15 Oct 2026 14:16:38 +0000 Message-ID: Date: Thu, 15 Oct 2026 07:16:34 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 01/18] x86/cpufeatures: Support Privilege Level Zero Association (PLZA) To: Babu Moger , , , CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , References: <6d0336754b14f33fbc3c5e276ffd7ab12e0d0435.1790867441.git.babu.moger@amd.com> Content-Language: en-US From: Reinette Chatre In-Reply-To: <6d0336754b14f33fbc3c5e276ffd7ab12e0d0435.1790867441.git.babu.moger@amd.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW3PR05CA0013.namprd05.prod.outlook.com (2603:10b6:303:2b::18) To SJ2PR11MB8370.namprd11.prod.outlook.com (2603:10b6:a03:540::20) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ2PR11MB8370:EE_|BL3PR11MB6531:EE_ X-MS-Office365-Filtering-Correlation-Id: 04336e8f-d2f0-42af-37c3-08df2ac6ed04 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|23010399003|1800799024|366016|7416014|376014|56012099006|11063799006|4143699003|261009223027099003|18002099003|10067099003|22082099003; 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This can stall forward progress and > eventually degrade overall system performance. > > AMD hardware supports a feature Privilege Level Zero Association (PLZA), > which allows the CPU's CLOSID and/or RMID association to be changed during > the transition from user mode to kernel mode. This allows the kernel to run > using a different CLOSID and/or RMID than user space, which can improve > system performance and/or allow kernel work to be monitored separately. > > Note that PLZA feature associates CLOSID and/or RMID to kernel work, and > therefore influences resource allocation and/or monitoring for all > resources, not only memory bandwidth. > > The feature is detected via CPUID_Fn80000020_EBX_x00 [Bit 9]: Privilege > Level Zero Association (PLZA). > > The PLZA feature details are documented in [1] available from [2]. > > [1] AMD64 Zen6 Platform Quality of Service (PQOS) Extensions: > Publication # 69193 Revision: 1.00, Issue Date: March 2026 > > Signed-off-by: Babu Moger > Acked-by: Borislav Petkov (AMD) > Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 # [2] > --- Reviewed-by: Reinette Chatre Reinette