Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 11 May 2022 09:02:40 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc:     "Tian, Kevin" <kevin.tian@intel.com>,
        Baolu Lu <baolu.lu@linux.intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        Christoph Hellwig <hch@infradead.org>,
        "Raj, Ashok" <ashok.raj@intel.com>, Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        "Jiang, Dave" <dave.jiang@intel.com>,
        Vinod Koul <vkoul@kernel.org>,
        Eric Auger <eric.auger@redhat.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        "Pan, Jacob jun" <jacob.jun.pan@intel.com>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v6 03/12] iommu: Add attach/detach_dev_pasid domain ops
Message-ID: <20220511120240.GY49344@nvidia.com>
References: <20220510061738.2761430-1-baolu.lu@linux.intel.com>
 <20220510061738.2761430-4-baolu.lu@linux.intel.com>
 <20220510140238.GD49344@nvidia.com>
 <f56ea479-aa82-37ae-91c3-754816a4ed8b@linux.intel.com>
 <BN9PR11MB5276100AC9BBB7DE5CB800CF8CC89@BN9PR11MB5276.namprd11.prod.outlook.com>
 <Yntrv+nq2t/IeVo2@myrica>
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Yntrv+nq2t/IeVo2@myrica>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?3roa3OlpHR/Y7jVkxarGRkXANyh9PWROjhU0tB0NnIANuGXH79BKNCE4t7oD?=
 =?us-ascii?Q?q49sB45XM53iKL1f+Nkem827IBMfy3FvbyW2IwkNbfXBnYgPmwI6tfDx6u0K?=
 =?us-ascii?Q?Ypi9/RAj+NB0gUfPCN/kWcBxZHdSpc80EYfnjxw8vKCPHRhGDvHTTW2cEk7J?=
 =?us-ascii?Q?AcR9jF03Uo9OdX5OOH4l8vT8aPoLv4RAtRecRKPs8uiJp0Y5i7DATxhJKfFJ?=
 =?us-ascii?Q?Rq4TdpEOoKJpfa9OVBvpGfOAsu0M9hOL7x2mvQiC94pBb2K9OstfdagtDW69?=
 =?us-ascii?Q?0vNei8pRIZU1+h4NI+m9UEZtLpmWKijPAv6BdqQrpU5biQ1MWjNFvzDc4/b7?=
 =?us-ascii?Q?YtuGmu3UTVwA/44dbswzuSEdSAH366NCzyL2VVpYJWPgcTlNBmuyKYWEBa+F?=
 =?us-ascii?Q?L2jXDjl0LsxAFknd3SMq68CboY7YhDiQg/F/Ddbd9PrvqGQmOKeOVQs40YG4?=
 =?us-ascii?Q?tEXbm52/t8VQf4MsBg3hxpyMDrceZFMR0Z8c5Ws7lqY8AMB7Js+OSNTBzhB/?=
 =?us-ascii?Q?YXmgjCgSBQu1R7C6wOGFgz1n6At9I0+Kz3Hj9G+FoGlQm+/TloaC/bfvvYQD?=
 =?us-ascii?Q?XeQHkjPzLuG+WnU/RMkddi9JRqM67y++x0Rahl+qQq6KKgg8MxSdTeHZEq2r?=
 =?us-ascii?Q?I71w/f6sAs2E3W5Hwn9UsCQ+h8v2BaRwWy2wXXyki93eMiuR2YLcD9SsK52h?=
 =?us-ascii?Q?V8sQyd8W+LuX3DpJp/ObkNBOdMvtcR2DXrj5y8VvlqhtKJ/4RVFGpP7HaJvB?=
 =?us-ascii?Q?kbIr5qRT17gZNKrVCqkh+WjmqOqjcsx863bujnBQzO7zcRboIUsnTzjbC8lr?=
 =?us-ascii?Q?7eZJ8O5t4zdGNPB6Y+1bqIcAZc7tCoA9LUMzXLP1rwahIbZXau37I5rqQEM8?=
 =?us-ascii?Q?o9wZjwfV/WFTU3ZemlS3Xq/eM1JoMOoFJoM9dQ8aeohcSHjeU6IdcQv8l2+b?=
 =?us-ascii?Q?5YMLymfVvqgFNX1L/Qmre1tU0EStaiHPaEOGb2QyfgR83EUbSAKuD6juXMDd?=
 =?us-ascii?Q?LU/ymWEvGqtsvTNyn//QcvDPDhBKKD9VH8pQEBtx4WTMdR1aD/OT9tCfPkH6?=
 =?us-ascii?Q?iDWvAQnr247mHnJf8Y9ch4nAfNCCCUaauRZTYtv8HHjSCwv81IB0QB6wRlBb?=
 =?us-ascii?Q?TwnAt4HJ59lhNGmKTOw+GCLZsXEetLIa5K0DpoFtvNMfL8LA9POojMadUwUQ?=
 =?us-ascii?Q?eVoBWxFghdsKc++tq3vOqN2y+9glfyShPzdO9mjpIcibQS3U7WpkGmUu+5YA?=
 =?us-ascii?Q?kHkdCwNJ/eOz5KwMJ7CUDXiUJrCU42d6jtdxVfhHp9qQJfNrgWABQiiTEwmT?=
 =?us-ascii?Q?VuXZbeMQHZfwqml2wUskfTOUCVmf/Q+9jCDXU2l7ZhaRW2kIQyKenIqvVgGF?=
 =?us-ascii?Q?xozZzDQ02Xkh0u0Cz2KfAbr3BePJW+RFWCtFuS0NYYXs3l7pEvgWryLlhxqF?=
 =?us-ascii?Q?6Iu3WAKFsscuL0Bup6morYoI15oWcGIQsaUJ+VQnvbIjCnHO8vfNRvwTldL1?=
 =?us-ascii?Q?EU23ESkZk+obyZxTjYhjMBB77pSfVSXpin8u/aDZV+n0M5QZIAqT0WGXv9SD?=
 =?us-ascii?Q?4e3snN3ElZ1iTr2wCPrROIy0y1QS1Gzj3/WHZu1yXfcuOMpL6FfKPu+83Vbo?=
 =?us-ascii?Q?0XMbJofzHHcI2xv5m07/2URWtaefx2vtgMMIaX9z7UdUtLpvNWrRRqlxcKE4?=
 =?us-ascii?Q?r4wp1yML9p+ojuL62yhvXE7nwL2HTtR2FaX2Hd1JFoXoyh9vAR1FUEfuVjjP?=
 =?us-ascii?Q?QYrJkXa1tQ=3D=3D?=
X-OriginatorOrg: Nvidia.com
X-MS-Exchange-CrossTenant-Network-Message-Id: e44549c0-6cb3-41c9-27a7-08da334626cb
X-MS-Exchange-CrossTenant-AuthSource: MN2PR12MB4192.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 May 2022 12:02:41.9484
 (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: /mhkCtXk7wiDvdiUAazg3H/pABFOvjlVTJGLA0k7R1n+ZB5jr3ONhJJ2s5IzML/t
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR12MB4952
X-Spam-Status: No, score=-1.7 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO,
        RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,
        T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=no autolearn_force=no
        version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, May 11, 2022 at 08:54:39AM +0100, Jean-Philippe Brucker wrote:
> > > > Then 'detach pasid' is:
> > > >
> > > > iommu_ops->blocking_domain->ops->attach_dev_pasid(domain, dev,
> > > pasid);
> > > >
> > > > And we move away from the notion of 'detach' and in the direction that
> > > > everything continuously has a domain set. PASID would logically
> > > > default to blocking_domain, though we wouldn't track this anywhere.
> > > 
> > > I am not sure whether we still need to keep the blocking domain concept
> > > when we are entering the new PASID world. Please allow me to wait and
> > > listen to more opinions.
> > > 
> > 
> > I'm with Jason on this direction. In concept after a PASID is detached it's
> > essentially blocked. Implementation-wise it doesn't prevent the iommu
> > driver from marking the PASID entry as non-present as doing in this
> > series instead of actually pointing to the empty page table of the block
> > domain. But api-wise it does make the entire semantics more consistent.
> 
> This is all internal to IOMMU so I don't think we should be concerned
> about API consistency. I prefer a straighforward detach() operation
> because that way IOMMU drivers don't have to keep track of which domain is
> attached to which PASID. That code can be factored into the IOMMU core.

Why would a driver need to keep additional tracking?

> In addition to clearing contexts, detach() also needs to invalidate TLBs,
> and for that the SMMU driver needs to know the old ASID (!= PASID) that
> was used by the context descriptor. We can certainly work around a missing
> detach() to implement this, but it will be convoluted.

It is not "missing" it is just renamed to blocking_domain->ops->set_dev_pasid()

The implementation of that function would be identical to
detach_dev_pasid.

Jason