Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 15 Oct 2021 08:09:56 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     "Tian, Kevin" <kevin.tian@intel.com>
Cc:     Lu Baolu <baolu.lu@linux.intel.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        "alex.williamson@redhat.com" <alex.williamson@redhat.com>,
        "hch@lst.de" <hch@lst.de>,
        "jasowang@redhat.com" <jasowang@redhat.com>,
        "joro@8bytes.org" <joro@8bytes.org>,
        "jean-philippe@linaro.org" <jean-philippe@linaro.org>,
        "parav@mellanox.com" <parav@mellanox.com>,
        "lkml@metux.net" <lkml@metux.net>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "lushenming@huawei.com" <lushenming@huawei.com>,
        "eric.auger@redhat.com" <eric.auger@redhat.com>,
        "corbet@lwn.net" <corbet@lwn.net>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "yi.l.liu@linux.intel.com" <yi.l.liu@linux.intel.com>,
        "Tian, Jun J" <jun.j.tian@intel.com>, "Wu, Hao" <hao.wu@intel.com>,
        "Jiang, Dave" <dave.jiang@intel.com>,
        "jacob.jun.pan@linux.intel.com" <jacob.jun.pan@linux.intel.com>,
        "kwankhede@nvidia.com" <kwankhede@nvidia.com>,
        "robin.murphy@arm.com" <robin.murphy@arm.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "dwmw2@infradead.org" <dwmw2@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "david@gibson.dropbear.id.au" <david@gibson.dropbear.id.au>,
        "nicolinc@nvidia.com" <nicolinc@nvidia.com>
Subject: Re: [RFC 06/20] iommu: Add iommu_device_init[exit]_user_dma
 interfaces
Message-ID: <20211015110956.GC2744544@nvidia.com>
References: <20210922123931.GI327412@nvidia.com>
 <BN9PR11MB5433CE19425E85E7F52093278CA79@BN9PR11MB5433.namprd11.prod.outlook.com>
 <20210927150928.GA1517957@nvidia.com>
 <BN9PR11MB54337B7F65B98C2335B806938CA89@BN9PR11MB5433.namprd11.prod.outlook.com>
 <20210928115751.GK964074@nvidia.com>
 <9a314095-3db9-30fc-2ed9-4e46d385036d@linux.intel.com>
 <20210928140712.GL964074@nvidia.com>
 <BN9PR11MB5433B8CB2F1EA1A2D06586588CA99@BN9PR11MB5433.namprd11.prod.outlook.com>
 <20210929125902.GU964074@nvidia.com>
 <BN9PR11MB5433C616093C8DDA5A859C2F8CB99@BN9PR11MB5433.namprd11.prod.outlook.com>
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <BN9PR11MB5433C616093C8DDA5A859C2F8CB99@BN9PR11MB5433.namprd11.prod.outlook.com>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?qub00jUJUs6zng9TKGjf4NT9VS50jbM97Osf/NC2ab2HsKawsnv5NjiwMXJk?=
 =?us-ascii?Q?tDnAHouVzc+DAe61gYJtrokxJBvHhqiKnATnj0dFsp97XFtKVKePqmHsffGm?=
 =?us-ascii?Q?CHpxFGCh0JNCdRhKhm0rblxUV6b7iRF1b5ANOL5K3Dv/PgJZDXYqSwA3rVZW?=
 =?us-ascii?Q?BZieAGbQLrO+f2Rv8MGiy0yGMrL18w3TGU2BANODNEy5erg8nPj3fHec7pUM?=
 =?us-ascii?Q?I2QA5cwFzozKwL7FD7tIFgduqDFgNuv73+b8ZoMLssCMvdaAXooq0EoPWM+R?=
 =?us-ascii?Q?E3Z2JcUrL9SobXyeGMyfu0IKcrqk9vtS8HHA9Zz93ZZ28ixVaxesu9Oqup/l?=
 =?us-ascii?Q?IGdSv39ib07YAmccjzZbfWb8pYKVZduRKaRuAwDwlts1Uicn6guwXVI2hPq7?=
 =?us-ascii?Q?LhwcQsCymhRvPoeVL8E7hvc0ZYDLFev5bY3IVfaScDkfm3iXR9s+DTrPiKwC?=
 =?us-ascii?Q?BIDa/lO8JNz1BJFrFo2N/Vk9WCS3TOMZp8pRIxwAI1OcCZgznXj0A/SgW7Ls?=
 =?us-ascii?Q?3FN6o+Wi4g9t0wX63AWnOZUApbzKdkFfFmM2f5OsSQSRYYV6pBac1PYq6EhE?=
 =?us-ascii?Q?IGFENI590pTzyD98LKDgZGuahWbogCvc9OfVb4nQm42/07olIVJahNQjvYBG?=
 =?us-ascii?Q?ho+9fBC7O4WTOpRhYl5yOREdMk+0W2HINj7J2DhXc4z4xmrnuIK4jJGZy0DK?=
 =?us-ascii?Q?CttfzIJVG1g2K+ItNf9+vhEnCMWqhZFMCw2t8WASZB6NwDzj7eR50eJYWIwf?=
 =?us-ascii?Q?KYVpGCH3YITBpLm8wmwJCoAdfpo4YmFsZZYnVcueDqZxALhD/Zp80Yq1P7N6?=
 =?us-ascii?Q?xI4pv5T900mbwWE3TCewdnOy21YwlasCZEZw0M64mlGDJvK0ntpncwXC6r8g?=
 =?us-ascii?Q?Z1DCuS9AfCFZr36ncHECk8ZsClj2o+CbSnMvhMInk6ntCw/qV07OgVAG7dGK?=
 =?us-ascii?Q?FWiWnnjgS1/wg92e9YgSEvQsxE/bFqyn6TpQ2JFdj88TOQGLMyI9e3GeOFan?=
 =?us-ascii?Q?UQa40/0V/I5lXGt/Jk41CNxDQzkdglJfNckGw7oI958381ilaGpzNTiF+OUO?=
 =?us-ascii?Q?76r20DcxoifXxq+yFubiNCBNFF0mc4lkAr38DT4K1uuJMdSynM131/y9V2T8?=
 =?us-ascii?Q?CQSKHX8tna5hUbNYuj7iIqaZ2snqyoyFO3mhv/1AI+rjciD43+pMm7HE1nNb?=
 =?us-ascii?Q?ZqsXDSIJj823pnvVRS0hmeqpzXN2Lb4TpQwV37mHC9ecwKta6/BjZdnaXfMs?=
 =?us-ascii?Q?oXfNcZEG3pgM3LVfAfPuzQJQbX304+99VFCxtQaK1CzfUznFYLXmycvqJNZi?=
 =?us-ascii?Q?Oy7hz85wLhQnRD8+yizuuEia?=
X-OriginatorOrg: Nvidia.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 390adfe9-b67f-4ecd-2571-08d98fcc529b
X-MS-Exchange-CrossTenant-AuthSource: BL0PR12MB5506.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Oct 2021 11:09:57.4094
 (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: 2I7or5PWkoOAXbQvCwn9d2OYV6LDbgP0T1XdB6c0IZEGTf2twLjWvx1PdYHFaJwK
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL1PR12MB5080
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, Oct 15, 2021 at 01:29:16AM +0000, Tian, Kevin wrote:
> Hi, Jason,
> 
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Wednesday, September 29, 2021 8:59 PM
> > 
> > On Wed, Sep 29, 2021 at 12:38:35AM +0000, Tian, Kevin wrote:
> > 
> > > /* If set the driver must call iommu_XX as the first action in probe() or
> > >   * before it attempts to do DMA
> > >   */
> > >  bool suppress_dma_owner:1;
> > 
> > It is not "attempts to do DMA" but more "operates the physical device
> > in any away"
> > 
> > Not having ownership means another entity could be using user space
> > DMA to manipulate the device state and attack the integrity of the
> > kernel's programming of the device.
> > 
> 
> Does suppress_kernel_dma sounds better than suppress_dma_owner?
> We found the latter causing some confusion when doing internal
> code review. Somehow this flag represents "don't claim the kernel dma
> ownership during driver binding". suppress_dma_owner sounds the
> entire ownership is disabled...

If in doubt make it

suppress_iommu_whatever_the_api_is_that_isn't_called

> Another thing is about DMA_OWNER_SHARED, which is set to indicate 
> no dma at all. Thinking more we feel that this flag is meaningless. Its
> sole purpose is to show compatibility to any USER/KERNEL ownership, 
> and essentially the same semantics as a device which is not bound to
> any driver. So we plan to remove it then pci-stub just needs one line 
> change to set the suppress flag. But want to check with you first in case
> any oversight.

It sounds reasonable, but also makes it much harder to find the few
places that have this special relationship - ie we can't grep for
DMA_OWNER_SHARED anymore.

Jason