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Mon, 17 Nov 2025 23:02:53 -0800 Date: Mon, 17 Nov 2025 23:02:52 -0800 From: Nicolin Chen To: Baolu Lu CC: , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v5 3/5] iommu: Add iommu_driver_get_domain_for_dev() helper Message-ID: References: <0303739735f3f49bcebc244804e9eeb82b1c41dc.1762835355.git.nicolinc@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ5PEPF000001C8:EE_|SJ0PR12MB6904:EE_ X-MS-Office365-Filtering-Correlation-Id: 7d25a5bf-bb2b-4e77-abb0-08de26708a7c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|36860700013|7416014|1800799024|376014|13003099007; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?3YvuBeJpjKx8nYEvFg3Zp/tqCEYzuLHT2jT6idOqZGmTWM/Y6tdfk8YgtgJH?= =?us-ascii?Q?x86clj0b6xL3mds2rzi8ZjQFN0xcbuydpd5/VSVZUBhdU62S8+bVT3EnBDoX?= =?us-ascii?Q?ps5+ukrF57hLrxantQpoIROlasWMHmjlsg+4titroYF1ayDoB7BwiqDZWPAt?= =?us-ascii?Q?kgfs/8M0OezNZpfFrzHQYjmaCHUqqHG+bndu3W67xPxo3sM67G6GBPxbvELA?= =?us-ascii?Q?Nogy5tLRZigFnnY/dkDVPpDc2fQFLQZiKT0OZRvBTOO9ptDRJwhb4wvB6PI1?= =?us-ascii?Q?ogQrxbE0CdtNEcyR9wOFyve9j68hYYYUhZt6iOaW3ewtaSEcSinI3FgMq3lA?= =?us-ascii?Q?9UmGbAdaHKp7VPsYqt6wNoIkMNUsO6NYtxS8yhJsNCl1e+vMYgpJwshWVDP9?= =?us-ascii?Q?FZTxnWQBCGyDVH/0oVQw6IkJXJ04R8fGK4smW4Sw9zg8NHKCEznyaPCGnJLp?= =?us-ascii?Q?vdjIqdVxUoOTBn7u4GOCy/ir98MVY9zhr9JQoo1ZlppnhtcVS2womHDhWlkU?= =?us-ascii?Q?PmnQ03XRkLyjQEbH9vBXX0Fdv1BpvEIKn2Q9b7mF2KNKg73TvtP++owRDxQY?= =?us-ascii?Q?/EVTA5RO5QI1urbmfyigiTWqycFd+M7QRYCGNyGel2qavFd/j3Hze8CllJz4?= =?us-ascii?Q?PyiBUSYsJZ4bFZ3fz5vIy7OWesSyiW3Rt+SPC1FvJ0Z8hN5g1FzRrdP8jENm?= =?us-ascii?Q?T+zvi4r9hFXTxGBI3shWvaoiBikOglEHUIZUgpGI0t33Emdkwvip/3YUuhrz?= =?us-ascii?Q?82iOUoF95JQW9CR/aA53ZAg6/QdV+gyuohNrpN0YhbvrzIvIQFd/gpdBPzZ0?= =?us-ascii?Q?1KSbjzJ5PEZYlknDMeX6fn1C7OaX/+pFlRt0IyDN0ouSK9sVTFOE4w+HO0T7?= =?us-ascii?Q?DTexzYToF0YMpIbh55QE3+ItMTRClSrJfrjjxbber7NbrW6vl9Xd10ZHe3nw?= =?us-ascii?Q?tgdeYe4wcgcJhtnH9tzz82YGm0dj774zlmdu/meiLeY4btgpGcYmbyutVLaG?= =?us-ascii?Q?kO55AqfrBEa4NZmungnxy78RfYKrDKC1tiMRgY8GtHn8WEBfZiInh+C3bp9k?= =?us-ascii?Q?9VmIopCtjRQ/KbdIA4F87SejXq7rVsrCJhg6hLMTWg5a+v5gSZLVO9CCgMjh?= =?us-ascii?Q?HqVWV9ZWJ4jV67w1vsJmdE1csg2zDmDh+eZnwv/+hMN22MEeaeYq1Fb77CDx?= =?us-ascii?Q?+/ijUAgxYdxSacUOnbwBKvc2NnZ3TA2GaWU0KL3TCXy0JZZQUhReXuRBK4cT?= =?us-ascii?Q?6gUKk44g0h1bBfAFJhJJUki5xTw0bEZGXLaZjWGuNwtX+pSdpP1bgIHfti88?= =?us-ascii?Q?3p+/MVJrAxlNdm0otsgba4OzqAmcJV+EQ3ZkWNP3v6zBCMVi4y97/2x7Hsry?= =?us-ascii?Q?maGmE+h5UagrrCU1LCv1V0gIalz4q/kddlIOV/7weHxfiLIpL3i6k1xB87qa?= =?us-ascii?Q?jnDu/nQxLEoEO3V1Ab3q8f1NfTfheoGY6kVNV14A4MHYc7mR62Lz1+ZksmOa?= =?us-ascii?Q?u7Ymk3oUvisLuk1UZznikDFMrwhVBj+YaTO4lWliVOwxvkRToQeUJom44n80?= =?us-ascii?Q?rz310WSTNc3azJSaErY+/0LTk5q89sKNpHPD4ei4?= X-Forefront-Antispam-Report: CIP:216.228.117.160;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge1.nvidia.com;CAT:NONE;SFS:(13230040)(82310400026)(36860700013)(7416014)(1800799024)(376014)(13003099007);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Nov 2025 07:03:13.3431 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 7d25a5bf-bb2b-4e77-abb0-08de26708a7c 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: SJ5PEPF000001C8.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR12MB6904 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251117_230321_830401_C2ECF1D3 X-CRM114-Status: GOOD ( 22.76 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Nov 12, 2025 at 09:41:25AM -0800, Nicolin Chen wrote: > Hi Baolu, > > On Wed, Nov 12, 2025 at 01:58:51PM +0800, Baolu Lu wrote: > > On 11/11/25 13:12, Nicolin Chen wrote: > > > +/** > > > + * iommu_get_domain_for_dev() - Return the DMA API domain pointer > > > + * @dev - Device to query > > > + * > > > + * This function can be called within a driver bound to dev. The returned > > > + * pointer is valid for the lifetime of the bound driver. > > > + * > > > + * It should not be called by drivers with driver_managed_dma = true. > > > > "driver_managed_dma != true" means the driver will use the default > > domain allocated by the iommu core during iommu probe. > > Hmm, I am not very sure. Jason's remarks pointed out that There > is an exception in host1x_client_iommu_detach(): > https://lore.kernel.org/all/20250924191055.GJ2617119@nvidia.com/ > > Where the group->domain could be NULL, i.e. not attached to the > default domain? > > > The iommu core > > ensures that this domain stored at group->domain will not be changed > > during the driver's whole lifecycle. That's reasonable. > > > > How about making some code to enforce this requirement? Something like > > below ... > > > > > + */ > > > struct iommu_domain *iommu_get_domain_for_dev(struct device *dev) > > > { > > > /* Caller must be a probed driver on dev */ > > > @@ -2225,10 +2234,29 @@ struct iommu_domain *iommu_get_domain_for_dev(struct device *dev) > > > if (!group) > > > return NULL; > > > + lockdep_assert_not_held(&group->mutex); > > > > ... > > if (WARN_ON(!dev->driver || !group->owner_cnt || group->owner)) > > return NULL; > > With that, could host1x_client_iommu_detach() trigger WARN_ON? Hi Baolu, For v6, I tend to keep this API as-is, trying not to give troubles to existing callers. Jason suggested a potential followup series: https://lore.kernel.org/linux-iommu/20250821131304.GM802098@nvidia.com/ That would replace this function, so maybe we can think about that. If you have a strong feeling about the WARN_ON, please let me know. Thanks Nicolin