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Thu, 5 Nov 2026 09:44:51 -0800 Received: from nvidia.com (10.127.8.13) by mail.nvidia.com (10.126.190.182) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.56 via Frontend Transport; Thu, 5 Nov 2026 09:44:45 -0800 Date: Thu, 5 Nov 2026 09:44:42 -0800 From: Nicolin Chen To: Aneesh Kumar K.V CC: Jason Gunthorpe , , Alex Williamson , Alexey Kardashevskiy , Bjorn Helgaas , Catalin Marinas , Jacob Pan , Joerg Roedel , "Jonathan Cameron" , Jonathan Hunter , "Kevin Tian" , Krishna Reddy , Lukas Wunner , Robin Murphy , Samuel Ortiz , Shameer Kolothum , Steven Price , Suravee Suthikulpanit , Suzuki K Poulose , Thierry Reding , "Vasant Hegde" , Will Deacon , Xu Yilun , , , , , , , Jonathan Corbet , Shuah Khan , Randy Dunlap Subject: Re: [PATCH v8 13/15] iommufd/viommu: Allow vIOMMUs without a parent HWPT Message-ID: References: <20261104161632.3547423-1-aneesh.kumar@kernel.org> <20261104161632.3547423-14-aneesh.kumar@kernel.org> <20261104193139.GB3889730@ziepe.ca> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; 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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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261105_094531_049883_B964ECFB X-CRM114-Status: GOOD ( 12.59 ) X-Spam-Score: -2.1 (--) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" X-Spam-Status: No, score=-10.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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