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Thu, 29 Jan 2026 18:57:33 +0000 Received: from LV8PR12MB9620.namprd12.prod.outlook.com ([fe80::299d:f5e0:3550:1528]) by LV8PR12MB9620.namprd12.prod.outlook.com ([fe80::299d:f5e0:3550:1528%5]) with mapi id 15.20.9564.010; Thu, 29 Jan 2026 18:57:33 +0000 Date: Thu, 29 Jan 2026 14:57:31 -0400 From: Jason Gunthorpe To: Matthew Brost Cc: intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org, leonro@nvidia.com, francois.dugast@intel.com, thomas.hellstrom@linux.intel.com, himal.prasad.ghimiray@intel.com Subject: Re: [RFC PATCH v3 06/11] drm/pagemap: Add IOVA interface to DRM pagemap Message-ID: <20260129185731.GA2333318@nvidia.com> References: <20260128004841.2436896-1-matthew.brost@intel.com> <20260128004841.2436896-7-matthew.brost@intel.com> <20260128151458.GJ1641016@ziepe.ca> <20260128193509.GU1641016@ziepe.ca> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-ClientProxiedBy: BL1P223CA0014.NAMP223.PROD.OUTLOOK.COM (2603:10b6:208:2c4::19) To LV8PR12MB9620.namprd12.prod.outlook.com (2603:10b6:408:2a1::19) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LV8PR12MB9620:EE_|CH3PR12MB8260:EE_ X-MS-Office365-Filtering-Correlation-Id: 2a7baaab-542b-4d03-a8ed-08de5f68425d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014; 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First, let me explain the > > > possible addressing modes on the UAL fabric: > > > > > > - Physical (akin to IOMMU passthrough) > > > - Virtual (akin to IOMMU enabled) > > > > > > Physical mode is straightforward — resolve the PFN to a cross-device > > > physical address, then install it into the initiator’s page tables along > > > with a bit indicating routing over the network. In this mode, the vfuncs > > > here are basically NOPs. > > > > Ugh of course they would invent something so complicated. > > Why wouldn't we... But conceptually really fairly close to IOMMU > paththrough vs. enabled. Why do you need address virtualization on the scale up fabric :( I can see access control but full virtualization sounds like overkill, especially considering how slow it will necessarily be compared to the fabric itself. We are already in a world where even PCI can't manage untranslated requests and a scale up fabric with 3TB/sec of bandwidth is somehow going to have address translation too? Doesn't seem reasonable. > > I'm not convinced this should be hidden inside DRM. The DMA API is the > > > Well, what I’m suggesting isn’t in DRM. A UAL API would be its own > layer, much like the DMA API. Of course we could stick this in the DMA > API and make it high-speed-fabric-generic, etc., but I do think the > fabric functions would have their own signatures and semantics (see my > explanation around device_ual_alloc reclaim rules, what locks it is > allowed to take, etc.). DMA API is already bus agnostic, I think there is no issue to plug in a ualink_device or whatever under there and make it do something sensible, and it would be *particularly* easy if the address translation can slot in as an attached iommu. Jason