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Wed, 12 Feb 2025 07:42:44 +0000 Message-ID: Date: Wed, 12 Feb 2025 15:47:57 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 09/14] iommu/vt-d: Add IOMMU_HWPT_ALLOC_PASID support To: Baolu Lu , , , CC: , , , , , , Suravee Suthikulpanit , Robin Murphy References: <20241219132746.16193-1-yi.l.liu@intel.com> <20241219132746.16193-10-yi.l.liu@intel.com> <38e26d9f-0727-4b15-8e1d-03d262c15c8c@linux.intel.com> <5c5180cb-9bbe-4fa7-b109-5dad2ca9516a@linux.intel.com> Content-Language: en-US From: Yi Liu In-Reply-To: <5c5180cb-9bbe-4fa7-b109-5dad2ca9516a@linux.intel.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: KL1PR0401CA0005.apcprd04.prod.outlook.com (2603:1096:820:f::10) To DS0PR11MB7529.namprd11.prod.outlook.com (2603:10b6:8:141::20) Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB7529:EE_|DS0PR11MB7831:EE_ X-MS-Office365-Filtering-Correlation-Id: b4fa72dd-b723-4b1e-c682-08dd4b38d62e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|366016; 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Would it be reasonable to >>>>> support page faults for nested domains? >>>> >>>> yeah, it's good to discuss it. >>>> >>>>> If so, perhaps it's time to open intel_iommu_domain_alloc_nested() to >>>>> support IOMMU_HWPT_FAULT_ID_VALID when PRI is enabled on the device? >>>> >>>> IMHO, the PRQ support for nested domains requires some more facility. PRQ >>>> can happen at either stage-1 or stage-2, iommu driver may need to tell >>>> it and forward to the correct domain (nested domain or parent domain). Or >>>> the stage-2 is always pinned just as the VFIO/iommufd does. Hence, any PRQ >>>> happens under nested translation should be due to stage-1. >>> >>> The parent domain is currently always pinned and does not yet support >>> page faults. Therefore, when a page fault occurs within a nested domain, >>> it apparently should be routed to user space... >>> >>> If we decide to support page faults on the stage-2 domain in the future, >>> we will need to figure out the correct destination of each page fault >>> and route it accordingly, either to the parent domain or the user space >>> nested domain. Hardware assistance would be beneficial, otherwise the >>> software may need to traverse the parent domain, which is not >>> performance friendly. >> >> this is my question. Is it still true the parent domain is always pinned >> after the below series? If yes, then it's fine to enable IOPF for nested >> domain. >> >> https://lore.kernel.org/linux-iommu/20241015-jag-iopfv8-v4-0- >> b696ca89ba29@kernel.org/ > > Then, perhaps we could enforce this in iommufd for a short-term purpose? > > When allocating a hwpt in iommufd, we should enforce that the flags > IOMMU_HWPT_ALLOC_NEST_PARENT and IOMMU_HWPT_FAULT_ID_VALID cannot be set > at the same time. Let's consult with other vendors. We need this enforcement because we lack a straightforward method to distinguish between PRIs in stage-1 and stage-2 under nested translation. If other vendors share this requirement, it would be appropriate to implement this enforcement in IOMMUFD. Otherwise, we may check it in intel iommu driver. @arm and amd folks. :) -- Regards, Yi Liu