RE: [RFC] /dev/ioasid uAPI proposal

[Tian, Kevin]

> From: Jason Gunthorpe
> Sent: Thursday, June 3, 2021 9:05 PM
> 
> > >
> > > 3) Device accepts any PASIDs from the guest. No
> > >    vPASID/pPASID translation is possible. (classic vfio_pci)
> > > 4) Device accepts any PASID from the guest and has an
> > >    internal vPASID/pPASID translation (enhanced vfio_pci)
> >
> > what is enhanced vfio_pci? In my writing this is for mdev
> > which doesn't support ENQCMD
> 
> This is a vfio_pci that mediates some element of the device interface
> to communicate the vPASID/pPASID table to the device, using Max's
> series for vfio_pci drivers to inject itself into VFIO.
> 
> For instance a device might send a message through the PF that the VF
> has a certain vPASID/pPASID translation table. This would be useful
> for devices that cannot use ENQCMD but still want to support migration
> and thus need vPASID.

I still don't quite get. If it's a PCI device why is PASID translation required?
Just delegate the per-RID PASID space to user as type-3 then migrating the 
vPASID space is just straightforward. 

Thanks
Kevin