RE: Plan for /dev/ioasid RFC v2

Tian, Kevin
2021-06-09T09:43:50Z

> From: Leon Romanovsky <leon@kernel.org>
> Sent: Wednesday, June 9, 2021 5:02 PM
>
> On Mon, Jun 07, 2021 at 02:58:18AM +0000, Tian, Kevin wrote:
> > Hi, all,
>
> <...>
>
> > (Remaining opens in v1)
>
> <...>
>
> > - Device-centric (Jason) vs. group-centric (David) uAPI. David is not fully
> > convinced yet. Based on discussion v2 will continue to have ioasid uAPI
> > being device-centric (but it's fine for vfio to be group-centric). A new
> > section will be added to elaborate this part;
>
> <...>
>
> > (Adopted suggestions)
>
> <...>
>
> > - (Jason) Addition of device label allows per-device capability/format
> > check before IOASIDs are created. This leads to another major uAPI
> > change in v2 - specify format info when creating an IOASID (mapping
> > protocol, nesting, coherent, etc.). User is expected to check per-device
> > format and then set proper format for IOASID upon to-be-attached
> > device;
>
> Sorry for my naive question, I still didn't read all v1 thread and maybe
> the answer is already written, but will ask anyway.
>
> Doesn't this adopted suggestion to allow device-specific configuration
> actually means that uAPI should be device-centric?
>
> User already needs to be aware of device, configure it explicitly, maybe
> gracefully clean it later, it looks like not so much left to be group-centric.
>

Yes, this is what v2 will lean toward. /dev/ioasid reports format info and
handle IOASID attachment per device. VFIO could still keep its group-
centric uAPI, but in the end it needs bind each device in the group to
IOASID FD one-by-one.

Thanks
Kevin