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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?M8SWigRHYUC8yl6HAnIA8Su/AH/qbLkHH2gQOpHWPBGBU6iDyONI24yONjxW?= =?us-ascii?Q?YrZUtvsGbFmERLOLuu4fKFJe7NHEDDSgZMmM8B2GjBcX7r982DhzXqjXEpbN?= =?us-ascii?Q?LFMocPuhHwJ4TzTtV3jxEYqxYT8l+85Y27SjHqsjXXaITKvoudN8cx8kpW2Y?= =?us-ascii?Q?r7HT5EYxCc30lPy/MCiEXg0MIVn9TmwalE/lHQwGXKjYYBpY+WZZewmWTgwx?= =?us-ascii?Q?SX5KtzYN9yH6OJ+LwIunM0fkqX/EK+JZGImGY9iVM7sHWJTYldRa1uRn2jCT?= =?us-ascii?Q?f7R3rdMLwnwq03P05j8I9cColcpuPeTJDeeNwhA14qQJ/akGf8cD1Y/AS8qf?= =?us-ascii?Q?d3gOZN9DXLIbxJmZKP0JizHyAllYdC0i91ASFbWelIRsvFAszeUhywou5ubG?= =?us-ascii?Q?yVD7KLa4xA6AsCz1DIdKvcRLS3MqZgvuSUlBZodmUZs4Aju3/UkHLFjIbshj?= =?us-ascii?Q?D6ytfUPBBMTU7rH4xzwwag5xabvhUDsI+J4+y6E3zGeUXatZeMGs4x3bMTl9?= =?us-ascii?Q?5qxdfRGKnOtQ6XwKaTjMfl5FmRWu9c7ACJQLxnXkykyExopGxGhmN9YFNvxe?= =?us-ascii?Q?K3rV6+WVZNOtELkXKEgad25LbPa3FRQA1yMZxDRfRr9vmaElln2UWZK2CpGc?= =?us-ascii?Q?J5XB7k+5NX9OHxIQDXlpRp3KWTUsVMu0wFiPfhVbQrFcKiOTets0tzkT42CB?= =?us-ascii?Q?Av4YLTXd28ZdZiqSdX1r0piADEZI9SJ9tPldZFC96ZWohlvexF0gzNdvKQN5?= =?us-ascii?Q?QtK7gKPJqwoFye67DhCKnErwdr2liBi4i0gBvt9Ho4uu+6vw7wZ7q3mIzL/8?= =?us-ascii?Q?C+u47WjB82DxgaUI3lQYHoz3RBoN6DPGU670yOwaRt64KcXHAFJGf79NYYoY?= =?us-ascii?Q?wf5ITTEvkNDfU6Lq0hOF3a58OZuhTfE6kS9UNmGIn5dK532bhl5ay70sf/dN?= =?us-ascii?Q?WSpta4rXyKKD2OsuO6pG9JUdoN26Buvii6LQyJQ+0FaG1qpeu5RQDJl+PKTX?= =?us-ascii?Q?0n5lR8/ZjwFBkDuNFM33XuB6blX6LQdLww2BNFmKlS4qyH61w2e8VoawtScT?= =?us-ascii?Q?uqG0C8hD6h+AXQoodb58QrM3vicrIAaRMP0aZuS9u0c/eMtuP6dJVmIRXX1b?= =?us-ascii?Q?ctZE1PKwTwihKL94QWOvfLtFAvaOY5Lk3x0CDLZLfNMePDwiSyk9NK3mV5DI?= =?us-ascii?Q?lGfliOTX8TXKnnzjAJx4xHHrVamXcK3SNsbaZnMtqM3sKGVv6ulepjTGgBTF?= =?us-ascii?Q?pQ+R2gC5tz/ccUvkpgHiHPXUziLmfQpJ+6nFpePKezuN5ERW3HyHgvzPeLw/?= =?us-ascii?Q?i1tP4ZQbGsMr6fea4eACxlsawej8Q9VodADY/oLyefv6jbl5HXNgNyPyDhnL?= =?us-ascii?Q?7+ZPyoU0f7OJVGNkXZU/C/mfapBGDcufgzGwQzLxpEeruvfz5QzXO9RGgU/6?= =?us-ascii?Q?8v3JUulFyiJY9/7QRHCTs+yJbrDL49mi7scY8SP1pAYPzYpFIhkmunNZrioK?= =?us-ascii?Q?zBZ7MIJyG7izvnb6OHwkZjga67Qzjsm6QWHU5bKqOzPhQpCZ8LGll78u90is?= =?us-ascii?Q?iHl8d01LJdoSXtYurNwcLXN8a60RYcvHJv+YKQvj9ruDFPbR70c+epclVC2d?= =?us-ascii?Q?Q/ajs1vYcBbIGDSBj1qHclITyKxOQEQAVLcWqVY6jvLjXrd5q4VM/vt2dfZ/?= =?us-ascii?Q?W8rlCaPMd9nf5Lc0uTVJrH/xH+9Gcq8N5XNDrQiXMIFtZzR/MYJcxtZzQoh/?= =?us-ascii?Q?NNClkmW+Ww=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 6129369d-becb-4d1a-3b0a-08da43154377 X-MS-Exchange-CrossTenant-AuthSource: MN2PR12MB4192.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 31 May 2022 14:53:03.3326 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 9OpIW/fUhuTi2Sp/HDSqgAJhVuLcP7kn1ZTevI59g/Vi6MPT82hkToNSTjJgpuFs X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN0PR12MB5737 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 31, 2022 at 10:11:18PM +0800, Baolu Lu wrote: > On 2022/5/31 21:10, Jason Gunthorpe wrote: > > On Tue, May 31, 2022 at 11:02:06AM +0800, Baolu Lu wrote: > > > > > For case 2, it is a bit weird. I tried to add a rwsem lock to make the > > > iommu_unmap() and dumping tables in debugfs exclusive. This does not > > > work because debugfs may depend on the DMA of the devices to work. It > > > seems that what we can do is to allow this race, but when we traverse > > > the page table in debugfs, we will check the validity of the physical > > > address retrieved from the page table entry. Then, the worst case is to > > > print some useless information. > > > > Sounds horrible, don't you have locking around the IOPTEs of some > > kind? How does updating them work reliably? > > There's no locking around updating the IOPTEs. The basic assumption is > that at any time, there's only a single thread manipulating the mappings > of the range specified in iommu_map/unmap() APIs. Therefore, the race > only exists when multiple ranges share some high-level IOPTEs. The IOMMU > driver updates those IOPTEs using the compare-and-exchange atomic > operation. Oh? Did I miss where that was documented as part of the iommu API? Daniel posted patches for VFIO to multi-thread iommu_domin mapping. iommufd goes out of its way to avoid this kind of serialization so that userspace can parallel map IOVA. I think if this is the requirement then the iommu API needs to provide a lock around the domain for the driver.. Jason