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Wed, 11 Sep 2024 12:52:20 -0700 Date: Wed, 11 Sep 2024 12:52:20 -0700 From: Nicolin Chen To: "Tian, Kevin" CC: "jgg@nvidia.com" , "corbet@lwn.net" , "iommu@lists.linux.dev" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Liu, Yi L" , "eric.auger@redhat.com" , "shameerali.kolothum.thodi@huawei.com" , "smostafa@google.com" , "baolu.lu@linux.intel.com" Subject: Re: [PATCH] Documentation: userspace-api: iommufd: Update HWPT_PAGING and HWPT_NESTED Message-ID: References: <20240910204111.7969-1-nicolinc@nvidia.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SA2PEPF00003F61:EE_|DM4PR12MB6088:EE_ X-MS-Office365-Filtering-Correlation-Id: 44e15f7c-a67b-4dd8-98d6-08dcd29b493d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|1800799024|36860700013|7416014|376014; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Sep 2024 19:52:36.8898 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 44e15f7c-a67b-4dd8-98d6-08dcd29b493d 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: SA2PEPF00003F61.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB6088 On Wed, Sep 11, 2024 at 08:06:48AM +0000, Tian, Kevin wrote: > > From: Nicolin Chen > > Sent: Wednesday, September 11, 2024 3:31 PM > > > > On Wed, Sep 11, 2024 at 07:09:15AM +0000, Tian, Kevin wrote: > > > > From: Nicolin Chen > > > > Sent: Wednesday, September 11, 2024 4:41 AM > > > > > > > > -3. IOMMUFD_OBJ_HW_PAGETABLE is created when an external driver > > calls > > > > the IOMMUFD > > > > +3. IOMMUFD_OBJ_HWPT_PAGING can be created in two ways: > > > > + > > > > + IOMMUFD_OBJ_HWPT_PAGING is created when an external driver > > calls > > > > the IOMMUFD > > > > kAPI to attach a bound device to an IOAS. Similarly the external driver > > uAPI > > > > allows userspace to initiate the attaching operation. If a compatible > > > > pagetable already exists then it is reused for the attachment. Otherwise > > a > > > > new pagetable object and iommu_domain is created. Successful > > > > completion of > > > > this operation sets up the linkages among IOAS, device and > > > > iommu_domain. Once > > > > - this completes the device could do DMA. > > > > - > > > > - Every iommu_domain inside the IOAS is also represented to userspace > > as > > > > a > > > > - HW_PAGETABLE object. > > > > + this completes the device could do DMA. Note that every > > iommu_domain > > > > inside > > > > + the IOAS is also represented to userspace as an > > > > IOMMUFD_OBJ_HWPT_PAGING. > > > > > > the last sentence is redundant. here we are talking about how > > HWPT_PAGING > > > is created so it's implied. probably you can state that HWPT_PAGING object > > > is created when talking about "otherwise a new page table object and > > > iommu_domain is created". > > > > I don't quite get this part...where is the redundancy? And where > > is "otherwise a new page table object .."? > > the original text: > > allows userspace to initiate the attaching operation. If a compatible > pagetable already exists then it is reused for the attachment. Otherwise a > new pagetable object and iommu_domain is created. Successful completion of > > it's clear to say that HWPT_PAGING object is created upon successful > completion there. Then naturally every iommu_domain in an IOAS > is represented to userspace as HWPT_PAGING. Not added by you > but could be cleaned up while at it. 😊 I see. I did this: +3. IOMMUFD_OBJ_HWPT_PAGING can be created in two ways: + + * IOMMUFD_OBJ_HWPT_PAGING is automatically created when an external driver + calls the IOMMUFD kAPI to attach a bound device to an IOAS. Similarly the + external driver uAPI allows userspace to initiate the attaching operation. + If a compatible member HWPT_PAGING object exists in the IOAS's HWPT_PAGING + list, then it will be reused. Otherwise a new HWPT_PAGING that represents + an iommu_domain to userspace will be created, and then added to the list. + Successful completion of this operation sets up the linkages among IOAS, + device and iommu_domain. Once this completes the device could do DMA. + + * IOMMUFD_OBJ_HWPT_PAGING can be manually created via the IOMMU_HWPT_ALLOC + uAPI, provided an ioas_id via @pt_id to associate the new HWPT_PAGING to + the corresponding IOAS object. The benefit of this manual allocation is to + allow allocation flags (defined in enum iommufd_hwpt_alloc_flags), e.g. it + allocates a nesting parent HWPT_PAGING if the IOMMU_HWPT_ALLOC_NEST_PARENT + flag is set. Thanks Nicolin