Re: Plan for /dev/ioasid RFC v2

[Jason Gunthorpe]

On Thu, Jun 24, 2021 at 02:37:31PM +1000, David Gibson wrote:
> On Thu, Jun 17, 2021 at 08:04:38PM -0300, Jason Gunthorpe wrote:
> > On Thu, Jun 17, 2021 at 03:02:33PM +1000, David Gibson wrote:
> > 
> > > In other words, do we really have use cases where we need to identify
> > > different devices IDs, even though we know they're not isolated.
> > 
> > I think when PASID is added in and all the complexity that brings, it
> > does become more important, yes.
> > 
> > At the minimum we should scope the complexity.
> > 
> > I'm not convinced it is so complicated, really it is just a single bit
> > of information toward userspace: 'all devices in this group must use
> > the same IOASID'
> 
> Um.. no?  You could have devA and devB sharing a RID, but then also
> sharing a group but not a RID with devC because of different isolation
> issues.  So you now have (at least) two levels of group structure to
> expose somehow.

Why? I don't need to micro optimize for broken systems. a/b/c can be
in the same group and the group can have the bit set. 

It is no worse than what we have today.

Jason