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Thu, 13 May 2021 03:28:52 +0000 From: "Tian, Kevin" To: Jason Gunthorpe , Christoph Hellwig CC: Joerg Roedel , Alex Williamson , David Woodhouse , Lu Baolu , Will Deacon , Kirti Wankhede , "linux-arm-kernel@lists.infradead.org" , "iommu@lists.linux-foundation.org" , "kvm@vger.kernel.org" Subject: RE: [PATCH 3/6] vfio: remove the unused mdev iommu hook Thread-Topic: [PATCH 3/6] vfio: remove the unused mdev iommu hook Thread-Index: AQHXRWldX98a1U6w60C1HwYkmNlXK6rc3tAAgAPcBcA= Date: Thu, 13 May 2021 03:28:52 +0000 Message-ID: References: <20210510065405.2334771-1-hch@lst.de> <20210510065405.2334771-4-hch@lst.de> <20210510155454.GA1096940@ziepe.ca> In-Reply-To: <20210510155454.GA1096940@ziepe.ca> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: dlp-version: 11.5.1.3 dlp-product: dlpe-windows dlp-reaction: no-action authentication-results: ziepe.ca; dkim=none (message not signed) header.d=none;ziepe.ca; dmarc=none action=none header.from=intel.com; x-originating-ip: [192.198.147.205] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: e1e4823e-5c2f-4069-14a8-08d915bf3b29 x-ms-traffictypediagnostic: CO1PR11MB5137: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:8882; 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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: MWHPR11MB1886.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: e1e4823e-5c2f-4069-14a8-08d915bf3b29 X-MS-Exchange-CrossTenant-originalarrivaltime: 13 May 2021 03:28:52.4490 (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: dsphs0/xFpQJkgLdLHXH6uIpuP0h3FnzYQ0BnZVqjv0PyF64VdxXILbNGVojtzUif0VPXQfM6obxCS1UQYFE1g== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CO1PR11MB5137 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org > From: Jason Gunthorpe > Sent: Monday, May 10, 2021 11:55 PM >=20 > On Mon, May 10, 2021 at 08:54:02AM +0200, Christoph Hellwig wrote: > > The iommu_device field in struct mdev_device has never been used > > since it was added more than 2 years ago. > > > > Signed-off-by: Christoph Hellwig > > --- > > drivers/vfio/vfio_iommu_type1.c | 132 ++++++-------------------------- > > include/linux/mdev.h | 20 ----- > > 2 files changed, 25 insertions(+), 127 deletions(-) >=20 > I asked Intel folks to deal with this a month ago: >=20 > https://lore.kernel.org/kvm/20210406200030.GA425310@nvidia.com/ >=20 > So lets just remove it, it is clearly a bad idea >=20 > Reviewed-by: Jason Gunthorpe >=20 Want to get a clearer picture on what needs to be redesigned after this removal. Are you specially concerned about this iommu_device hack which=20 directly connects mdev_device to iommu layer or the entire removed logic including the aux domain concept? For the former we are now=20 following up the referred thread to find a clean way. But for the latter=20 we feel it's still necessary regardless of how iommu interface is redesigne= d=20 to support device connection from the upper level driver. The reason is=20 that with mdev or subdevice one physical device could be attached to=20 multiple domains now. there could be a primary domain with DOMAIN_ DMA type for DMA_API use by parent driver itself, and multiple auxiliary=20 domains with DOMAIN_UNMANAGED types for subdevices assigned to=20 different VMs. In this case It's a different model from existing policy=20 which allows only one domain per device. In removed code we followed=20 Joerg's suggestion to keep existing iommu_attach_device for connecting=20 device to the primary domain and then add new iommu_aux_attach_ device for connecting device to auxiliary domains. Lots of removed iommu=20 code deal with the management of auxiliary domains in the iommu core=20 layer and intel-iommu drivers, which imho is largely generic and could be leveraged w/o intrusive refactoring to support redesigned iommu=20 interface. Does it sound a reasonable position? Thanks Kevin