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Mon, 9 Mar 2026 06:40:07 -0500 Message-ID: <9145b8b7-fb83-49c4-aa17-acdba069359a@amd.com> Date: Mon, 9 Mar 2026 17:10:06 +0530 Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/5] perf/amd/ibs: Avoid calling perf_allow_kernel() from the IBS NMI handler To: Michael Petlan CC: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Ian Rogers , Dapeng Mi , James Clark , Sadasivan Shaiju , , , , "Manali Shukla" , Santosh Shukla , Ananth Narayan , Sandipan Das , Ravi Bangoria References: <20260216042216.1440-1-ravi.bangoria@amd.com> <20260216042216.1440-5-ravi.bangoria@amd.com> <81204aa7-9d81-8d53-b82b-6c4ad8c89c2@redhat.com> Content-Language: en-US From: Ravi Bangoria In-Reply-To: <81204aa7-9d81-8d53-b82b-6c4ad8c89c2@redhat.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH1PEPF0000AD7A:EE_|LV8PR12MB9619:EE_ X-MS-Office365-Filtering-Correlation-Id: b4ab8452-ca55-413f-daf9-08de7dd0a05c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|82310400026|36860700016|1800799024; X-Microsoft-Antispam-Message-Info: UIwNzSpUl/F3VT9gi80bxwVObtuu6rz8Y9m6MkG8o1POALfLKNru/R5HC691y7fq5VwV4KuA6i5iBJ+4000/IYaTfl65uxVNJ6h9B+Tppse9C4a1bRsLmdzagj+Llr/d4/Ee099XWD/DKf3tOcXmo6trkULLdG2gRW942Pj07WeyX+CjvU77ClzlGvIx0mEA03MXg3QsyN7caDoBw9z1efxfJ0aPn8zIls8GYjgG8sebDd7t8p340Hp/w5ESeDNMAX4UBBnnv0OFhFNk3I4wCW0ZCUDY63Yi9pZYwkStCKVzA9gbs7aA3wG9JCApq8Cp4J9M6Yzd6n7+Yd9vR4LeiDih7QfQcWRJiI2GNT2mvTnqgHCQzUrbZneWah5WHxoODubNIFFP6w71J98qugyZg1oMPl3ze7FQJyy+Bn8miBVJvEZNYT1A/J8cseWf4JFM6XZniUlg0YjKrX5saNX/hRLJ7ocKaCQiJVZa30bKiyB4CW9UkH0/Wz+aFESbFL1HbtSrbnWoUTxugmcEeVhoAu/HkCm6LltfW1vlTrE2VOVs7+Tj+HNZITebBwpaEfljW/jOXKWHBFpQXT0TIRIPjdHnSHOwS6Gp3II3KRPFUxjPFE8aUYcUIOcdTJJgA77BIbrTI84TECBL7f2QO6AamexmyTZGaWUbMATzqgcJLTFI7O4BHdghbzy5h3bY5QSV8fEWJwRHNx1/Hga65huBV8284VfyPkoKeuyPKdyXqu6ot4RdEb90FSoEp2EZdN0zOTy4LYm7JGHPszY5a+L0Ow== X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb08.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(376014)(7416014)(82310400026)(36860700016)(1800799024);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: tDCDOjVI1LDH42b1GMvPoIurO1ExUde1dWmoNIoV2tbdWYjaZXCy8wWcSCjh1zEFVV45gEdkj4zUCxWO0c58oSjZ33+wl+G2f2ABzERSCGThteVvrBY027UdZK7NIsxI6tCyGEbP+7OJPSS0Ibyjjqd4v9PEQnenB3PGRLLaVN5fLZAr6EE5mz+JGvnRE9wO59xMXrleh9TxfDDvY3qmY3qLZdjqJZUM7SA1LnQIdx7DkX+lkCZVf/kf9EZmVvBemmV3kOR5vD3q8zuFnImMoER9djBuhDf1It9RMaooHLsz0Iuy9SBicsBCDX2bsHldZugvwY+dr4PAeGKj+KdMTb7HmFPb319ULV5EoJawSa1wQQs2VGLwJ5VHglNaLGdQdO4OxoQMCuf6md5F2hQDM8JeKvDNRQHPLOAhoNjw1aBYHTTySg+oaViQtqZ+ZIz/ X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Mar 2026 11:40:12.9982 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: b4ab8452-ca55-413f-daf9-08de7dd0a05c X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CH1PEPF0000AD7A.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV8PR12MB9619 Hi Michael, > By evaluating the privileges at the event-init moment and using cached > value later, couldn't it lead to the cached value being obsolete at > some point? E.g. a setuid program later dropping the privileges but > still being able to read physical addresses? Yes, but wouldn't the same concern apply to all other call sites of perf_allow_kernel() ? Thanks, Ravi