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

David Gibson
2021-04-28T02:41:56Z

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On Tue, Apr 27, 2021 at 01:39:54PM -0300, Jason Gunthorpe wrote:
> 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.

Ok, that makes sense.

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
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