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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?hr7sYkZK7JmRPuF7AOi7inrJDuFi1goWnynUV1yL0JDKPgP7M849xtWUOqh+?= =?us-ascii?Q?LPu6SaJdqFzJRTeKrKQM+WEz7+aqMoPcimQ9kTQKKx9poInCiXlzbNtYuZQp?= =?us-ascii?Q?3dpAeA1XTMZVpWjenSNipp/HNF3FNLWCz97FVg83ZO3Y+br5Y6NOEpm4nNa1?= =?us-ascii?Q?vc4Q+64t1ji6TXrHIv6SkfAnMO1Hxpb/Se0BPxtqcd0myMI72ZSDenZLz6mK?= =?us-ascii?Q?3GKrZlTS9/24NSm7WteHM7EW76Hp9Z2x8vggI/YlsLXl8qcreXT2s7+r3lYn?= =?us-ascii?Q?XmuFnp5ZRZd2bu+h6Nit1fBRS5QmDRCSv+Hof5DIgWYHUd6831WLdCS/gDfX?= =?us-ascii?Q?1j/RPqaNqhMv4SrDCco+6dfm5VmOCw8wEOQzDzuQduc/0c+FVR99P0BVEkCL?= =?us-ascii?Q?ayohBwRNQXLham/epi7TT8YUy6eb3VoVwhzrW85drHj+deZzuqFk9QsFdlQW?= =?us-ascii?Q?+L6Fs8PtkSV1wU0VWNHEEpwHMLr3EYe8NUTqhKkIk1v37eI9O979T4TzTkiB?= =?us-ascii?Q?tX0aojsIRg2U1Z/5g2cHUltF5bZ4T4WgI48Zyb8Vp8sU1CXJe8PUIJwzjiqU?= =?us-ascii?Q?h1h5+jchRQYsiaLd//xDE+YVGWDqJVemKtIKUW439W9OklMWadgcas4LcDek?= =?us-ascii?Q?g6F56ROD3xU45wftQi93LOu8SD79qSo5bPr3eW2P2dg8cVBWjukpYDqObBGv?= =?us-ascii?Q?JQY8zaC5r3XGiSpjcxUZbENblaDLUre3HkL35seC2qe8rIdIsclRPIFCS5bj?= =?us-ascii?Q?UZsC4FaKdxyE5XEKjKCzp7VayoKhlrHyIt/TMrFcN3jcF7HigBxdcmuhGqQ7?= =?us-ascii?Q?zWJZeT2mqfobagqQ5QWfheruq47yklr24RCf98xbqhuSnajFi2zf6+FGEB02?= =?us-ascii?Q?gl/5x1GTstXErIViyQtoQt/q/p3MeBrKlbsd5u1WDuaGWwnPAuRVwRqdXz5a?= =?us-ascii?Q?xkzOJLIXnD+YM9uUPl625zc/1p32bTAdZvOZ9/rct9jsSdnOIhpFBeExsVfM?= =?us-ascii?Q?hdf3r7jKw7rzQpQy7uYsP/GIMk4ivZjoZpg73k2FP8j7RJWc5lxH+XJFMANl?= =?us-ascii?Q?h+n7QNez/ta2qz49nlLvmiaMpBbN+OjP/DUSjnvrK0mjOTwS4qxOQpQX49IZ?= =?us-ascii?Q?mAz7cX1YjAjd+aZdtz3Leg6H73Ds0nItogI8EZF6LSlzEcHKh1+RQTheI6o4?= =?us-ascii?Q?+DpBei/QLQm+xcrc62SRKWQFeOvGM+u15igIGo6LfnImuUU22E/Wjn1A7yYE?= =?us-ascii?Q?rpC47+JnNNbMQbj/eM393NnUG8oXo8qBniBQVLlO2e/SwpmWJdN811hX9gw3?= =?us-ascii?Q?OjdX/NMd5b1kX4GhM3uyok17zxgJ+kfCP2Rg/20yVnq8hzmJ8503Huze0gkU?= =?us-ascii?Q?vUNpyNnLbPgUMjILcb07nEF9oEcd/kWAOJ2YOl4YsObXbz7HYIhlknuo74Tv?= =?us-ascii?Q?RDex7L2wmgMIZLQveBM+hwyfKwsEYpNBfY7lsf0TUyQNvls4ZS2dbHUDWrO1?= =?us-ascii?Q?+NItz4VCkPgf5neYvxqfzy9LcXuEtJW/j766xflwekWN7T5/v203v19oNhi7?= =?us-ascii?Q?SZMjbPQCmkigiAeilW3EUF6k3U+Gres0f9vZWTMz?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: fb4e6071-8626-46ef-398a-08daf40f36ca X-MS-Exchange-CrossTenant-AuthSource: LV2PR12MB5869.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Jan 2023 20:05:40.9286 (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: 2amaGh9cLYLxLHhDrwLRXuqsnwMeboU0vUKiM+cDrZ5uJZ7BA70JF0V+9GR7/ewI X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR12MB4935 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 11, 2023 at 07:54:51PM +0000, Sean Christopherson wrote: > Something feels off. If KVM's refcount is 0, then accessing device->group->kvm > in vfio_device_open() can't happen unless there's a refcounting bug somewhere. The problem is in close, not open. Specifically it would be very hard to avoid holding the group_lock during close which is when the put is done. > Rather than force devices to get KVM references, why not handle that in common > VFIO code and drop KVM refcountin from devices? Worst case scenario KVM is pinned > by a device that doesn't need KVM but is in a group associated with KVM. If that's > a concern, it seems easy enough to add a flag to vfio_device_ops to enumerate > whether or not the device depends on KVM. We can't make cross-dependencies between kvm and core VFIO - it is why so much of this is soo ugly. The few device drivers that unavoidably have KVM involvment already have a KVM module dependency, so they can safely do the get/put Jason