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;
IronPort-SDR: DvUXpg9Z5lj3tGCOI33YqoOkoipi4EWSKL3gC5cHU93sNJeo5lb8o4hBC3oGRIDnTEjqxC0iXC
 V7lTW4RPvC8w==
IronPort-SDR: jRsk+mnRHA+16n4Vwp48FtD2PwJG5+lZ5DxAiKSFcqotvTs40U+ETWaCG17FodTTa/53LI16vb
 d3B8lKIDWf1Q==
From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     Jason Gunthorpe <jgg@nvidia.com>,
        David Gibson <david@gibson.dropbear.id.au>
CC:     Alex Williamson <alex.williamson@redhat.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        Auger Eric <eric.auger@redhat.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        David Woodhouse <dwmw2@infradead.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
        Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        Jonathan Corbet <corbet@lwn.net>,
        "Raj, Ashok" <ashok.raj@intel.com>, "Wu, Hao" <hao.wu@intel.com>,
        "Jiang, Dave" <dave.jiang@intel.com>,
        "Alexey Kardashevskiy" <aik@ozlabs.ru>
Subject: RE: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation
 APIs
Thread-Topic: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs
Thread-Index: AQHXDZub0CDG82VGXUmLEYgvMuPs4KqKkLIAgACg94CAAC72gIAAD04AgAADogCAAErUgIAETQEAgAOaswCAB7C3gIAAhxQwgADYDACAATCSAIAAVGMAgAELsQCAACiXgIAAVBgAgAAaMwCAAAESAIAABy2AgAAgOYCAFdCAgIAAppUAgADsNgCAACqygIAHsmaAgAAzsYCAAAjdgIAAD/yAgAAcQgCAADqggIABMLWAgAAMMYCAABwXgIAABlIAgAAsEgCAABE9AIAGpToAgADKIACAAObmgA==
Date:   Wed, 28 Apr 2021 07:47:56 +0000
Message-ID: <MWHPR11MB1886C9199AA3F00FF72ACB508C409@MWHPR11MB1886.namprd11.prod.outlook.com>
References: <20210421175203.GN1370958@nvidia.com>
 <20210421133312.15307c44@redhat.com> <20210421230301.GP1370958@nvidia.com>
 <20210422111337.6ac3624d@redhat.com> <20210422175715.GA1370958@nvidia.com>
 <20210422133747.23322269@redhat.com> <20210422200024.GC1370958@nvidia.com>
 <20210422163808.2d173225@redhat.com> <20210422233950.GD1370958@nvidia.com>
 <YIecXkaEGNgICePO@yekko.fritz.box> <20210427171212.GD1370958@nvidia.com>
In-Reply-To: <20210427171212.GD1370958@nvidia.com>
Accept-Language: en-US
Content-Language: en-US
dlp-version: 11.5.1.3
dlp-product: dlpe-windows
dlp-reaction: no-action
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: fb10c083-cd2d-4b83-4eaa-08d90a19efe5
X-MS-Exchange-CrossTenant-originalarrivaltime: 28 Apr 2021 07:47:56.2719
 (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: UtI6aDH/bnX0XTvxGEgxQoNroWf5wY058TcATyWvHZiEHWc13rasxH33jbG6SakGlLItflHuiORuIURLGIV4Kw==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CO1PR11MB4915
X-OriginatorOrg: intel.com
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Wednesday, April 28, 2021 1:12 AM
>=20
[...]
> One option is VFIO can keep its group FD but nothing else will have
> anthing like it. However I don't much like the idea that VFIO will
> have a special and unique programming model to do that same things
> other subsystem will do. That will make it harder for userspace to
> implement.

Hi, Jason,

I have a question here. Based on discussions so far, it's clearly that the
new ioasid uAPI will differ from existing VFIO uAPI a lot, e.g. ioasid-
centric operations, no group fd, no incompatible domains, etc. Then=20
I wonder how we plan to support legacy VFIO applications in this=20
transition phase. Earlier you ever mentioned the desire of directly
replacing /dev/vfio/vfio with /dev/ioasid and having ioasid to present
both VFIO and new uAPI. Doesn't it imply that we have to copy the=20
VFIO container/group semantics into /dev/ioasid although it's a special=20
programming model only for VFIO?

Alternatively we could keep all the container/group legacy within VFIO
and having /dev/ioasid support only the new uAPI semantics. In this case
VFIO will include a shim iommu backend to connect its legacy uAPI into=20
drivers/ioasid backend functions for backward compatibility. Then VFIO
will also support a new model which only uses its device uAPI to bind
to new ioasid fd w/o using any legacy container/group/iommu uAPI.
Does this sound a plan?=20

Thanks
Kevin