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Thu, 23 Sep 2021 11:27:18 +0000 Received: from BL0PR12MB5506.namprd12.prod.outlook.com ([fe80::e8af:232:915e:2f95]) by BL0PR12MB5506.namprd12.prod.outlook.com ([fe80::e8af:232:915e:2f95%8]) with mapi id 15.20.4544.015; Thu, 23 Sep 2021 11:27:18 +0000 Date: Thu, 23 Sep 2021 08:27:16 -0300 From: Jason Gunthorpe To: Jean-Philippe Brucker Cc: "Tian, Kevin" , Alex Williamson , "Liu, Yi L" , "hch@lst.de" , "jasowang@redhat.com" , "joro@8bytes.org" , "parav@mellanox.com" , "lkml@metux.net" , "pbonzini@redhat.com" , "lushenming@huawei.com" , "eric.auger@redhat.com" , "corbet@lwn.net" , "Raj, Ashok" , "yi.l.liu@linux.intel.com" , "Tian, Jun J" , "Wu, Hao" , "Jiang, Dave" , "jacob.jun.pan@linux.intel.com" , "kwankhede@nvidia.com" , "robin.murphy@arm.com" , "kvm@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "dwmw2@infradead.org" , "linux-kernel@vger.kernel.org" , "baolu.lu@linux.intel.com" , "david@gibson.dropbear.id.au" , "nicolinc@nvidia.com" Subject: Re: [RFC 10/20] iommu/iommufd: Add IOMMU_DEVICE_GET_INFO Message-ID: <20210923112716.GE964074@nvidia.com> References: <20210919063848.1476776-1-yi.l.liu@intel.com> <20210919063848.1476776-11-yi.l.liu@intel.com> <20210922152407.1bfa6ff7.alex.williamson@redhat.com> <20210922234954.GB964074@nvidia.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?pC9gAMM6iD8O6S5wmHn8+gSBP+HXIcvO5TxISG0ZOypTaNPDn1FYmyJZHXgb?= =?us-ascii?Q?P3BZ49nYz8SDxso10KIoRuz3nEuESsjO8v9fgJKNz52x+RT70NyQ2lXzUqMP?= =?us-ascii?Q?+XNxsQcVeYMcHCmO5t7yOZA6PoqNPWwQRSe2zykZ3Fl+YQtycjQoAAd8n+VD?= =?us-ascii?Q?7UZgKW/q5nSG94YbcDJGIoRAMxOYoqB+QXqOA6qeNuaphx7IktZbJi76Wb3k?= =?us-ascii?Q?b/o0EFZDeJLLX8ctHZn3laU7C2J3vB3Ns9F6azsMw3YKeNChuhDzXhPISS95?= =?us-ascii?Q?P5pabjfY2D6xT5lEsl0bSsVwqIMFg+TI+03asOIw0j77zIcokLg70s+sAmUu?= =?us-ascii?Q?3hfYkIkEFeniEUKNSkgf8g4YdRjBUkEb2KYuOIRKKlEHdYGlUoscWPogtoKz?= =?us-ascii?Q?4fXrO7+8zvSXad+hhEhkXaNZP+P7GXop3voILWUUwrPkxAjfH/rSr89+z8n4?= =?us-ascii?Q?13AZhHIG5CkRFIwj1nY2Iu6MR60rtmv6f9YqUerSmw5yw7D4wBiX3gEKOjsk?= =?us-ascii?Q?LOnVux47qDGEWuTOqaeoCTUj9WhHJx7q9ytS4JoYK5esBAS6lmoYxgfJkMOt?= =?us-ascii?Q?plnYPDJ9RNtPMUwc4YQzc0hOh1h15qfWfkWwu6YmAKDTzlgzHzywqzVHpJsy?= =?us-ascii?Q?l6WNjTVyKOB4TcO3mUrd/sZkKI9cVYlutOCv8t1a1ijk6i2q25Y5gC+y5MOT?= =?us-ascii?Q?Fed4JrtCpYfUqeJpDfnXJfq1sIsKOgKxEMQ237klrj20PX12QBnUNUL3hpiv?= =?us-ascii?Q?llPopHCTYuLp7v8e7oo2wjSoYFMYbkJZ+Q4MAkzk9JdNd9y0QGAaf7h5XnA4?= =?us-ascii?Q?CoCfys4q2cq+tD5ngfwNKe7R6GGPF2WgIZWiP2hkZCvlbuURFSyc/OJ8n+DR?= =?us-ascii?Q?Y+YVjB2+7gFz2O+62iFmpnCugXA+FDJzdnVtGrTjTsifPm6xg9DfVOeDPRsJ?= =?us-ascii?Q?JjN0Rbb+hpcl6VPA9GIDEKL2HrYctsMYLwrQa8UI4gjpDU3cgDAP8NfcX1IZ?= =?us-ascii?Q?/Nk4vgBBPle7kn/6u/L0wCYhqU72pHzCTwGIV4dJfAQGlkjzg+5HgjqoWikw?= =?us-ascii?Q?5QnIbndJRlkSGhaXZIOBBPiAHl3WcYJ79gxaoIjpNkDsiwvEvPAIFvYGFohk?= =?us-ascii?Q?X36HfCefmWTCbwNAxugT+74SDQ9DpcGoRKVyHGzTvsozj7aKsCI4eCweU+f+?= =?us-ascii?Q?zJ7g+ROYVcQ9PfIyQ93MB1/RZuQS9IgL0Dzx05ACo7zjCtcpTFGCuqSXusCI?= =?us-ascii?Q?zL6hUlu1W47aowDjPnGRP/jWGdKQh8GVHqfxipTZVZ/YARMsLO7NOrWN1hKP?= =?us-ascii?Q?L1lciYfR87NyOmwh0TeLGJ+2?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: bd1e458e-e515-4132-f645-08d97e8519ee X-MS-Exchange-CrossTenant-AuthSource: BL0PR12MB5506.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Sep 2021 11:27:18.3882 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: fr1VvfeT5xYexIRk00zT6CQ8A6LRbnpze5Pkftj0lCVgXmsIcnBASPztpTi2QABM X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL0PR12MB5556 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 23, 2021 at 11:15:24AM +0100, Jean-Philippe Brucker wrote: > So we can only tell userspace "No_snoop is not supported" (provided we > even want to allow them to enable No_snoop). Users in control of stage-1 > tables can create non-cacheable mappings through MAIR attributes. My point is that ARM is using IOMMU_CACHE to control the overall cachability of the DMA ie not specifying IOMMU_CACHE requires using the arch specific DMA cache flushers. Intel never uses arch specifc DMA cache flushers, and instead is abusing IOMMU_CACHE to mean IOMMU_BLOCK_NO_SNOOP on DMA that is always cachable. These are different things and need different bits. Since the ARM path has a lot more code supporting it, I'd suggest Intel should change their code to use IOMMU_BLOCK_NO_SNOOP and abandon IOMMU_CACHE. Which clarifies what to do here as uAPI - these things need to have different bits and Intel's should still have NO SNOOP in the name. What the no-snoop bit is called on other busses can be clarified in comments if that case ever arises. 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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Thu, Sep 23, 2021 at 11:15:24AM +0100, Jean-Philippe Brucker wrote: > So we can only tell userspace "No_snoop is not supported" (provided we > even want to allow them to enable No_snoop). Users in control of stage-1 > tables can create non-cacheable mappings through MAIR attributes. My point is that ARM is using IOMMU_CACHE to control the overall cachability of the DMA ie not specifying IOMMU_CACHE requires using the arch specific DMA cache flushers. Intel never uses arch specifc DMA cache flushers, and instead is abusing IOMMU_CACHE to mean IOMMU_BLOCK_NO_SNOOP on DMA that is always cachable. These are different things and need different bits. Since the ARM path has a lot more code supporting it, I'd suggest Intel should change their code to use IOMMU_BLOCK_NO_SNOOP and abandon IOMMU_CACHE. Which clarifies what to do here as uAPI - these things need to have different bits and Intel's should still have NO SNOOP in the name. What the no-snoop bit is called on other busses can be clarified in comments if that case ever arises. Jason _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu