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Wed, 4 Nov 2026 11:03:49 -0800 Received: from nvidia.com (10.127.8.9) by mail.nvidia.com (10.129.68.8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.56 via Frontend Transport; Wed, 4 Nov 2026 11:03:44 -0800 Date: Wed, 4 Nov 2026 11:03:41 -0800 From: Nicolin Chen To: "Aneesh Kumar K.V (Arm)" CC: , Alex Williamson , "Alexey Kardashevskiy" , Bjorn Helgaas , "Catalin Marinas" , Jacob Pan , Jason Gunthorpe , 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> 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: N0ltwa1yXlZ9KAYHSJXEsDWdLJuQ0Eax9EBMOGnjIVBBjrJXrOz+Ljhw+Y09Y/Uu/+U/K5y2B3RWHF3V3aoyqFtk9uuCBWcAsHX1XKqm8VwbA9gbPl32F9ZPSIW/5uDjhlB4zp88C4AE8wDiKD9td6O84uYcnPavBUuUfVdr7vIM8yEspk7+GTgJA+OlxsxW+8dD367hCt1SS+sUHO1yzf8DFF6KpQy/qOsOY3PxdIqOlpxgSRWZUVChwjAE8FE16vB+fHUvokZ6ykp0W/VmooN+wbqzVLMquEeB/cZpTHTorgFE17OVFmqxt0drnoguubtHnRN5wDuRDw5SWzKDW2Z1UZbjju+9LzmUXAdEBX+jcRi5lusRVMvQcP/mAHKdzWFOXLQYZZCUQXTT1hWHCBwVz6JX//rY4ZOhuEYXJrXB3aMT0yKDghz0ylyx/2Vv X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Nov 2026 19:04:12.2941 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 0b146ec5-1378-47df-7523-08df3aa669d0 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CH01EPF000BE94D.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB8124 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261104_110422_032542_B6B3775A X-CRM114-Status: GOOD ( 10.98 ) 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=-5.9 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,SPF_HELO_NONE, SPF_PASS autolearn=no 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 Wed, Nov 04, 2026 at 09:46:30PM +0530, Aneesh Kumar K.V (Arm) wrote: > VIOMMU_ALLOC currently requires a nesting parent HWPT_PAGING even when > the selected vIOMMU implementation has no use for one. This would force > implementations such as the following Arm Realm vIOMMU to create an > unused parent. IIRC, MSI on ARM still goes through the NS pathway. So, it wouldn't be "unused" if the device attaches to it (or its nested hwpts)? By dropping the nesting parent from VIOMMU, it just simplifies the attachment to an S1 paging hwpt, right? Nicolin