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client-ip=165.204.84.17; helo=satlexmb08.amd.com; pr=C Received: from satlexmb08.amd.com (165.204.84.17) by SJ5PEPF000001E8.mail.protection.outlook.com (10.167.242.196) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9678.18 via Frontend Transport; Tue, 10 Mar 2026 16:46:10 +0000 Received: from satlexmb10.amd.com (10.181.42.219) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.17; Tue, 10 Mar 2026 11:46:10 -0500 Received: from satlexmb07.amd.com (10.181.42.216) by satlexmb10.amd.com (10.181.42.219) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.17; Tue, 10 Mar 2026 11:46:09 -0500 Received: from [10.252.223.199] (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server id 15.2.2562.17 via Frontend Transport; Tue, 10 Mar 2026 11:46:05 -0500 Message-ID: <9b49bfb2-8f0f-4831-943e-a82d10007680@amd.com> Date: Tue, 10 Mar 2026 22:16:04 +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> <9145b8b7-fb83-49c4-aa17-acdba069359a@amd.com> <21f41878-254f-191e-eaa9-26a9faf68d45@redhat.com> Content-Language: en-US From: Ravi Bangoria In-Reply-To: <21f41878-254f-191e-eaa9-26a9faf68d45@redhat.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: IGDZqU49kvsk/xiGKouu9erS5rWIszYi/s2tBfNZVmwAEhWCTTMLEWMxSJzUpZ0QT4cCrfULWCkwbvtUnSal2lv9dhUGyqRsD6hjMMUFn/to1laaSn5/IbM9//YpLEmpDrVI0YvGUvdzGDjjwkpFOEqwY9RvaY08MN9jIo+QvtKCS2T+jDZBCbRUpGhjPrVuGQxkltAi5RbtFi9fDzxh+QYF0lairPQFOBvDj3Klu95XsMYN8bLFfttgaWbivpnnhjXmCSvEar330Pbpibwv4THVI8+MuT+Bmo6AWWlQ2IoI7Ne7ACn9UXzKgfwgMM6d5q9v2bZOnwadNvlucZYik298vbhV1DJPTv9YPXb6NGsok/VPRxSF8QKU77G1aBC+TtLTswnIblh+3k5SUE+iF6TdqrJPH8W8pV8TmSSOr9/M1cNMxCzoTuE9ytNmM0vV X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Mar 2026 16:46:10.3982 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 6fbc5999-df0d-4336-2b6f-08de7ec488ab 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: SJ5PEPF000001E8.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR12MB9515 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() ? > > Well, I don't say this case is worse than the others, just raising a > more generic question whether this design is fairly acceptable or would > deserve e.g. privilege adjusting at the time when they are dropped or > something... Nothing more, just a note... :) I understand. However, performing the privilege check at the beginning and then continuing to allow accessing the privileged resource even after privileges have been dropped is a common design pattern, isn't it? For example, I assume something like this is allowed: fd = open("/root/only/file"); setresuid(); /* drop the privilege */ read(fd); Thanks, Ravi