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dkim=none (message not signed) header.d=none;intel.com; dmarc=none action=none header.from=nvidia.com; Received: from BL0PR12MB5506.namprd12.prod.outlook.com (2603:10b6:208:1cb::22) by BL0PR12MB5539.namprd12.prod.outlook.com (2603:10b6:208:1c3::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4544.14; Mon, 27 Sep 2021 13:09:36 +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 15.20.4544.021; Mon, 27 Sep 2021 13:09:36 +0000 Date: Mon, 27 Sep 2021 10:09:35 -0300 From: Jason Gunthorpe To: "Tian, Kevin" Cc: "Liu, Yi L" , "alex.williamson@redhat.com" , "hch@lst.de" , "jasowang@redhat.com" , "joro@8bytes.org" , "jean-philippe@linaro.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 06/20] iommu: Add iommu_device_init[exit]_user_dma interfaces Message-ID: <20210927130935.GZ964074@nvidia.com> References: <20210919063848.1476776-1-yi.l.liu@intel.com> <20210919063848.1476776-7-yi.l.liu@intel.com> <20210921170943.GS327412@nvidia.com> <20210922123931.GI327412@nvidia.com> <20210927115342.GW964074@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?UjDfeb01+UqvmaxxeRPCtEv07zQOBThVAwYy2zvpn2kMCPqBVt6XOktEmZy0?= =?us-ascii?Q?RxSXTHAfObOWz10WR5lA7Nb6+0MmqdQhGYbgWp684z2BvJepQ5EulWiRh66U?= =?us-ascii?Q?RItboFwJf2CxzVlHbsE8bwBjv9HQOG+Q9GkuZVdPuwK5om5AA12T/AkkBkAz?= =?us-ascii?Q?AzV6ydJuD/hauHI/91UwJjrJlbw+vni3x3xzu2AUd2SZzxbUIdNLA+LeOF1L?= =?us-ascii?Q?U8iBsWjWkShyVMZPlhZnflJSkajIwNJd11WWa5Lb9Jk3GTxUmwwVN4UTFdsZ?= =?us-ascii?Q?Qy+boR5as9p1JJOrGrnl2V/UkOTCJ0f3cFdr51QBYo4Voue10KtWouztYUSG?= =?us-ascii?Q?Mn5w57fUSf3/uSSVoCDaPiRD872ElJoogxr+1636exMJEtcgdcQkeLEAxJuP?= =?us-ascii?Q?Q26GB+MM/vpb1qaiSt6rb3InoOO47ae2citV4fA0BNiDZHrsozl8FBAu+syj?= =?us-ascii?Q?6qmyn8EY6/g+lZpDhBqDlS70ND9YspaLCYLvJJEJHzbyggmD30mfvqPfjQQ+?= =?us-ascii?Q?NzLGYdYNoUqvkv3MLx5iP3GAPx34bjdqEreAtz/W5j7hSG3HygDFLmcEVpnz?= =?us-ascii?Q?gf4ZkYYlKqlSyhUfzkeMA64E/kZ/0TraBvZmJsW9wztyN4ilQ5185RJs1QjV?= =?us-ascii?Q?n9CnMKiQDZpNzKRAP8UhvLAOdSEwT9RcZvySrWJtpUcMvySw2gW2GaIBZf54?= =?us-ascii?Q?0Z5TruMTcsJOwaxoAsfYUbX6lBTHK4ApJjELQuh2cTsl210kB8eNLZpLWtDD?= =?us-ascii?Q?f+C8+rZT+aLKXTxWQFdMYyhdTRH07aKv3jLfTuRw2hjL/VDIHGj1qxEcTyo1?= =?us-ascii?Q?y9pAgSNGWPomdrJDouDR5WdIaoCynKGeFeAkbrDBhC30/blU5shEgRogubx7?= =?us-ascii?Q?1HOZm/T24pVWrga0eraWCUBP1S3ACiTHvtoluShKXFMBmXqAehE5KdkWNsrU?= =?us-ascii?Q?Xz9GeUzpy/LdyjFvEmFMpql3ZU0+BoHfQJwFbKZin3GU2BIVjG6t8S03U7Ns?= =?us-ascii?Q?FPlNdJCSqNwByWPWPe64jTbTNlUVDapuEJiQwpZ5iBtfveCGLwGlvFpoMkQa?= =?us-ascii?Q?4DEbK4Dmbkr3ALK8Vo4llaQDT7DQlKAAv4TVYq8dsrYjOZNMBHderICBMbqT?= =?us-ascii?Q?U5zZhpQiLW80GqAq5x1WPA9JxpwW6zxcebpQGE4RGCn4gOH2I75bB206lFB6?= =?us-ascii?Q?gB22//83kU3Fy7kMWDJKkLHNE5OkHTODv7rpBITYLXADdOw49LAqoUvTHE2l?= =?us-ascii?Q?yae8Tv7VkXR1cwpBfZsAq7bw51gxB+Lctlm7eUvJxs4Z+sajtp4oi2HJuo6+?= =?us-ascii?Q?PBcSpPQ57opRcSmxMO/3ihQO?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 202543a6-b1f4-4557-9bf7-08d981b80e47 X-MS-Exchange-CrossTenant-AuthSource: BL0PR12MB5506.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Sep 2021 13:09:36.5833 (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: eDmdSqHZv/2vDB69GOIa4WXkznhzLsFk5yQG6fCnJwZA1rSFT8g4nFKp7BkAE52s X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL0PR12MB5539 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 27, 2021 at 01:00:08PM +0000, Tian, Kevin wrote: > > I think for such a narrow usage you should not change the struct > > device_driver. Just have pci_stub call a function to flip back to user > > mode. > > Here we want to ensure that kernel dma should be blocked > if the group is already marked for user-dma. If we just blindly > do it for any driver at this point (as you commented earlier): > > + ret = iommu_set_kernel_ownership(dev); > + if (ret) > + return ret; > > how would pci-stub reach its function to indicate that it doesn't > do dma and flip back? > Do you envision a simpler policy that no driver can be bound > to the group if it's already set for user-dma? what about vfio-pci > itself? Yes.. I'm not sure there is a good use case to allow the stub drivers to load/unload while a VFIO is running. At least, not a strong enough one to justify a global change to the driver core.. > > > +static int iommu_dev_viable(struct device *dev, void *data) > > > +{ > > > + enum dma_hint hint = *data; > > > + struct device_driver *drv = READ_ONCE(dev->driver); > > > > Especially since this isn't locked properly or safe. > > I have the same worry when copying from vfio. Not sure how > vfio gets safe with this approach... Fixing the locking in vfio_dev_viable is part of deleting the unbound list. Once it properly uses the device_lock and doesn't race with the driver core like this things are much better. Don't copy this stuff into the iommu core without fixing it. https://github.com/jgunthorpe/linux/commit/fa6abb318ccca114da12c0b5b123c99131ace926 https://github.com/jgunthorpe/linux/commit/45980bd90b023d1eea56df70d1c395bdf4cc7cf1 I can't remember if the above is contingent on some of the mdev cleanups or not.. Have to get back to it. Jason