On Tue, Mar 15, 2022 at 12:29:02PM -0400, Matthew Rosato wrote: > On 3/15/22 10:38 AM, Jason Gunthorpe wrote: > > On Tue, Mar 15, 2022 at 09:49:01AM -0400, Matthew Rosato wrote: > > > > > The rationale for splitting steps 1 and 2 are that VFIO_SET_IOMMU doesn't > > > have a mechanism for specifying more than the type as an arg, no? Otherwise > > > yes, you could specify a kvm fd at this point and it would have some other > > > advantages (e.g. skip notifier). But we still can't use the IOMMU for > > > mapping until step 3. > > > > Stuff like this is why I'd be much happier if this could join our > > iommfd project so we can have clean modeling of the multiple iommu_domains. > > > > I'd certainly be willing to collaborate so feel free to loop me in on the > discussions; Sure, I have you on my list. I've been waiting for Eric to get a bit further along on his ARM work so you have something appropriate to look at. In the mean time you can certainly work out the driver details as you've been doing here and hacking through VFIO. The iommu_domain logic is the big work item in this series, not the integration with the uAPI. > but I got the impression that iommufd is not close to ready (maybe > I'm wrong?) Well, quite alot has been done already and I think we are getting close to having something that can start moving forward, but yes it will not be "tomorrow". > -- if so I really don't want to completely delay this zPCI support > behind it as it has a significant benefit for kvm guests on s390x :( Every platform vendor is trying to do this exact same performance optimization. s390 is doing it a bit different, but as we've seen, not fundamentally so compard to ARM and Intel IOMMU's with HW nesting. I'm not sure that s390 should jump the queue and hacky hacky uAPIs all over the place. ARM platform has been working on this for literal years now. Jason
