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Thu, 13 Nov 2025 15:26:03 -0800 Date: Thu, 13 Nov 2025 15:26:02 -0800 From: Nicolin Chen To: Jason Gunthorpe CC: Alex Williamson , Christian =?iso-8859-1?Q?K=F6nig?= , , , Joerg Roedel , Kevin Tian , , , , , Robin Murphy , "Shuah Khan" , Sumit Semwal , Will Deacon , Krishnakant Jaju , Leon Romanovsky , Matt Ochs , , Simona Vetter , Vivek Kasireddy , Xu Yilun Subject: Re: [PATCH 4/9] iommufd: Allow a DMABUF to be revoked Message-ID: References: <0-v1-af84a3ab44f5+f68-iommufd_buf_jgg@nvidia.com> <4-v1-af84a3ab44f5+f68-iommufd_buf_jgg@nvidia.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <4-v1-af84a3ab44f5+f68-iommufd_buf_jgg@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CY4PEPF0000E9DA:EE_|MN0PR12MB6104:EE_ X-MS-Office365-Filtering-Correlation-Id: 73145002-edf2-409f-ebe0-08de230c1081 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|36860700013|7416014|376014|82310400026; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Nov 2025 23:26:25.5417 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 73145002-edf2-409f-ebe0-08de230c1081 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.160];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CY4PEPF0000E9DA.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN0PR12MB6104 On Fri, Nov 07, 2025 at 12:49:36PM -0400, Jason Gunthorpe wrote: > When connected to VFIO, the only DMABUF exporter that is accepted, the > move_notify callback will be made when VFIO wants to remove access to the > MMIO. This is being called revoke. > > Wire up revoke to go through all the iommu_domain's that have mapped the > DMABUF and unmap them. > > The locking here is unpleasant, since the existing locking scheme was > designed to come from the iopt through the area to the pages we cannot use > pages as starting point for the locking. There is no way to obtain the > domains_rwsem before obtaining the pages mutex to reliably use the > existing domains_itree. > > Solve this problem by adding a new tracking structure just for DMABUF > revoke. Record a linked list of areas and domains inside the pages > mutex. Clean the entries on the list during revoke. The map/unmaps are now > all done under a pages mutex while updating the tracking linked list so > nothing can get out of sync. Only one lock is required for revoke > processing. > > Signed-off-by: Jason Gunthorpe Reviewed-by: Nicolin Chen