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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: d8hVi+JscFBs+QaBybuTlRigcLAcKy2HynGk25s1LVRsOE5rH98CtxLmjNcHxqQzJVqFn0JhZvf9952aEP78Bx4yaD6crkAra8gxsc9XivfjrLsnbHKu8jusPirxlodPWAdymUfJBqKYnBlJblnPN0ZvrKVhFOYv1nQthLfozvahNhQYpsVJyFqdhPvTRCq/tK1W+a6UfcmEA3fN7220E+wIYM5RGrXxFJVTXXR3io0ihwcIbv7C2PuWJQahTJQ5iYJEQLpyytRfnbZ4th3Z8NZOC1nvUKZ9GkkSc/rCyqj4r9/OpdpvggujAgJnbRcUqOk7bKM8nQklnRgBhGJSvdBB5bAyrjvMnhqSpb4Bsh85aHMWJtPE5YtMhB+50IMDz7vqMF7zqz1dmcHYpTXHQXu0OcBMJoxB9N5QarM3V6A25hBnOsnLy2aChDGMRbzM X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Nov 2026 17:45:17.5609 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 54cb11e0-a066-4517-c3ef-08df3b648e1f X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.118.233];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN7PEPF000000A5.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB6660 On Thu, Nov 05, 2026 at 10:58:06AM +0530, Aneesh Kumar K.V wrote: > Jason Gunthorpe writes: > > On Wed, Nov 04, 2026 at 11:03:41AM -0800, Nicolin Chen wrote: > >> By dropping the nesting parent from VIOMMU, it just simplifies the > >> attachment to an S1 paging hwpt, right? > > > > Yes. > > > > The VMM must always maintain a S1 paging attachment that is the > > identity map of the VM on all devices, same action as when there is no > > viommu. > > > > I am currently creating an S2 paging attachment. This results in a > configuration with S1 disabled and S2 enabled, which is used by all > untrusted devices. For validation, that would work. Yet "no viommu" should would be S1 paging, i.e. hwpt allocated without IOMMU_HWPT_ALLOC_NEST_PARENT. For reference, QEMU has this: https://github.com/qemu/qemu/blob/master/hw/vfio/iommufd.c#L467 Thanks Nicolin