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Fri, 15 Oct 2021 01:29:17 +0000 From: "Tian, Kevin" To: Jason Gunthorpe CC: Lu Baolu , "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" , "david@gibson.dropbear.id.au" , "nicolinc@nvidia.com" Subject: RE: [RFC 06/20] iommu: Add iommu_device_init[exit]_user_dma interfaces Thread-Topic: [RFC 06/20] iommu: Add iommu_device_init[exit]_user_dma interfaces Thread-Index: AQHXrSF9WDj+Z+DU+UqMJ7tQK2EdmauuvK2AgACKnbCAALw6gIAHYVYAgACkNwCAAQ1OQIAAT36AgAAbKoCAAAj5AIAAq5rggADTsACAGGANEA== Date: Fri, 15 Oct 2021 01:29:16 +0000 Message-ID: References: <20210921170943.GS327412@nvidia.com> <20210922123931.GI327412@nvidia.com> <20210927150928.GA1517957@nvidia.com> <20210928115751.GK964074@nvidia.com> <9a314095-3db9-30fc-2ed9-4e46d385036d@linux.intel.com> <20210928140712.GL964074@nvidia.com> <20210929125902.GU964074@nvidia.com> In-Reply-To: <20210929125902.GU964074@nvidia.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: dlp-version: 11.6.200.16 dlp-product: dlpe-windows dlp-reaction: no-action authentication-results: nvidia.com; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BN9PR11MB5433.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 0ac29195-0dbf-4952-3c38-08d98f7b3449 X-MS-Exchange-CrossTenant-originalarrivaltime: 15 Oct 2021 01:29:16.8320 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: 2Al97JljauGF4GJSuqQWnX2hTZBY6NxZJjbrlf/8uzhgEfghVU4lbTU9JqIaKUoXsTBH+krIL++uAnQTLtEU/Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN7PR11MB2850 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Jason, > From: Jason Gunthorpe > Sent: Wednesday, September 29, 2021 8:59 PM >=20 > On Wed, Sep 29, 2021 at 12:38:35AM +0000, Tian, Kevin wrote: >=20 > > /* 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; >=20 > It is not "attempts to do DMA" but more "operates the physical device > in any away" >=20 > 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. >=20 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... Another thing is about DMA_OWNER_SHARED, which is set to indicate=20 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,=20 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=20 change to set the suppress flag. But want to check with you first in case any oversight. Thanks Kevin