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Wed, 25 Jun 2025 10:33:11 -0700 Received: from Asurada-Nvidia (10.127.8.13) by mail.nvidia.com (10.126.190.180) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.14 via Frontend Transport; Wed, 25 Jun 2025 10:33:10 -0700 Date: Wed, 25 Jun 2025 10:33:09 -0700 From: Nicolin Chen To: "Tian, Kevin" CC: "jgg@nvidia.com" , "corbet@lwn.net" , "will@kernel.org" , "bagasdotme@gmail.com" , "robin.murphy@arm.com" , "joro@8bytes.org" , "thierry.reding@gmail.com" , "vdumpa@nvidia.com" , "jonathanh@nvidia.com" , "shuah@kernel.org" , "jsnitsel@redhat.com" , "nathan@kernel.org" , "peterz@infradead.org" , "Liu, Yi L" , "mshavit@google.com" , "praan@google.com" , "zhangzekun11@huawei.com" , "iommu@lists.linux.dev" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-tegra@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "patches@lists.linux.dev" , "mochs@nvidia.com" , "alok.a.tiwari@oracle.com" , "vasant.hegde@amd.com" , "dwmw2@infradead.org" , "baolu.lu@linux.intel.com" Subject: Re: [PATCH v6 06/25] iommufd/access: Allow access->ops to be NULL for internal use Message-ID: References: Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Jun 2025 17:33:20.2388 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: fc3bf00f-a8b4-4a94-0640-08ddb40e60de 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: BL02EPF0001A101.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ1PR12MB6243 On Wed, Jun 25, 2025 at 09:37:18AM -0700, Nicolin Chen wrote: > On Wed, Jun 25, 2025 at 03:38:19AM +0000, Tian, Kevin wrote: > > > From: Nicolin Chen > > > Sent: Saturday, June 14, 2025 3:15 PM > > > > > > +int iommufd_access_notify_unmap(struct io_pagetable *iopt, unsigned long > > > iova, > > > + unsigned long length) > > > { > > > struct iommufd_ioas *ioas = > > > container_of(iopt, struct iommufd_ioas, iopt); > > > struct iommufd_access *access; > > > unsigned long index; > > > + int ret = 0; > > > > > > xa_lock(&ioas->iopt.access_list); > > > xa_for_each(&ioas->iopt.access_list, index, access) { > > > + if (!access->ops || !access->ops->unmap) { > > > + ret = -EBUSY; > > > + goto unlock; > > > + } > > > > then accesses before this one have been notified to unpin the area > > while accesses afterwards are left unnotified. > > > > in the end the unmap fails but with some side-effect incurred. > > > > I'm not sure whether this intermediate state may lead to any undesired > > effect later. Just raise it in case you or Jason already thought about it. > > That's a good point. When an access blocks the unmap, there is no > unmap happening so no point in notifying devices for ops->unmap. > > And, when the function is re-entered, there could be a duplicated > ops->unmap call for those devices that are already notified once? > > So, if we play safe, there can be a standalone xa_for_each to dig > for !access->ops->unmap. And it could be a bit cleaner to add an > iommufd_access_has_internal_use() to be called under those rwsems. Correct: it has to be under the xa_lock. So, this pre-check needs to be done in this function. Thanks Nicolin