Re: [RFC] /dev/ioasid uAPI proposal

Jason Gunthorpe
2021-06-04T12:09:10Z

On Fri, Jun 04, 2021 at 06:37:26AM +0000, Tian, Kevin wrote:
> > 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.

This is only possible if we get rid of the global pPASID allocation
(honestly is my preference as it makes the HW a lot simpler)

Without vPASID the migration would need pPASID's on the RID that are
guarenteed free.

Jason