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Wed, 18 Mar 2026 12:26:35 -0700 Received: from Asurada-Nvidia (10.127.8.9) by mail.nvidia.com (10.126.190.182) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.20 via Frontend Transport; Wed, 18 Mar 2026 12:26:34 -0700 Date: Wed, 18 Mar 2026 12:26:33 -0700 From: Nicolin Chen To: "Tian, Kevin" CC: "will@kernel.org" , "robin.murphy@arm.com" , "joro@8bytes.org" , "bhelgaas@google.com" , "jgg@nvidia.com" , "rafael@kernel.org" , "lenb@kernel.org" , "praan@google.com" , "baolu.lu@linux.intel.com" , "xueshuai@linux.alibaba.com" , "linux-arm-kernel@lists.infradead.org" , "iommu@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "linux-acpi@vger.kernel.org" , "linux-pci@vger.kernel.org" , Vikram Sethi Subject: Re: [PATCH v2 4/7] iommu/arm-smmu-v3: Mark ATC invalidate timeouts via lockless bitmap Message-ID: References: <0c5525367cc67ccc84a675544d1d9f8462704065.1773774441.git.nicolinc@nvidia.com> Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: YYlLSu6Ay2AZCfHdpZjmCPd1LRUdoerWDCwvm7yMnHXz8YM7yECpr0ABychwB1LO9HZBoHPmp/7557T6jNVT9di+LHO2/Fr8xqaHXv528CAmg0AV3HeaCz/AtPpfMBarSrRs0+8jsMazmfUu4l5jufe4fub1GqlUFprmehdNzaRNJkaOnv7ef8D9C/HYQzZ1xUCCk1XLKdUfPB8YruRtgHDp2FAd39jc785e5Mqq4ZvI8AHG3jGFFm6M858tlifsouCl9B4ikzNcEMnEucLNo/ToM1wzuydBfhuNmDokQPC555twsAgVjP1V/ny2HVsZrmLtMlGG4FnxVp2u7cg3ZmrnDj2eH4Pba91ZoYShfx9kA3073o8GYbV/4MBeg7IMYV9lFSBCJhTjEum9wsrNXQHpS+4W2jjscAqfNffIsB05oV0LuwxFd2Tc+/hY8HyO X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Mar 2026 19:26:49.9538 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 9e883f9f-3ee2-4691-b448-08de85244d8f X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.118.232];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: SJ5PEPF000001F0.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB7348 On Wed, Mar 18, 2026 at 07:36:20AM +0000, Tian, Kevin wrote: > > From: Nicolin Chen > > Sent: Wednesday, March 18, 2026 3:16 AM > > > > An ATC invalidation timeout is a fatal error. While the SMMUv3 hardware is > > aware of the timeout via a GERROR interrupt, the driver thread issuing the > > commands lacks a direct mechanism to verify whether its specific batch was > > the cause or not, as polling the CMD_SYNC status doesn't natively return a > > failure code, making it very difficult to coordinate per-device recovery. > > > > Introduce an atc_sync_timeouts bitmap in the cmdq structure to bridge this > > gap. When the ISR detects an ATC timeout, set the bit corresponding to the > > physical CMDQ index of the faulting CMD_SYNC command. > > > > It's nice to see the ability of allowing sw to identify the faulting sync command > upon an ATC timeout! On VT-d it's not feasible when multiple wait descriptors > (similar to CMD_SYNC) are in-fly... :/ Actually SMMU doesn't know which device is faulting when CMD_SYNC follows ATC_INV commands for multiple devices. The commit message in PATCH-7 describes this in the end. So Jason suggested to retry those ATC_INV commands by bisecting them per-device, which allows us to pinpoint which device. Could VT-d do the same? Nicolin