Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Apr 27, 2021 at 03:11:25PM +1000, David Gibson wrote:

> > So your proposal sort of moves the entire container/group/domain 
> > managment into /dev/ioasid and then leaves vfio only provide device
> > specific uAPI. An ioasid represents a page table (address space), thus 
> > is equivalent to the scope of VFIO container.
> 
> Right.  I don't really know how /dev/iosasid is supposed to work, and
> so far I don't see how it conceptually differs from a container.  What
> is it adding?

There are three motivating topics:
 1) /dev/vfio/vfio is only usable by VFIO and we have many interesting
    use cases now where we need the same thing usable outside VFIO
 2) /dev/vfio/vfio does not support modern stuff like PASID and
    updating to support that is going to be a big change, like adding
    multiple IOASIDs so they can be modeled as as a tree inside a
    single FD
 3) I understand there is some desire to revise the uAPI here a bit,
    ie Alex mentioned the poor mapping performance.

I would say it is not conceptually different from what VFIO calls a
container, it is just a different uAPI with the goal to be cross
subsystem.

Jason