RE: [PATCH v2 0/4] vfio-pci support pasid attach/detach

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> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Wednesday, April 17, 2024 1:50 AM
> 
> On Tue, Apr 16, 2024 at 08:38:50AM +0000, Tian, Kevin wrote:
> > > From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> > > Sent: Friday, April 12, 2024 4:21 PM
> > >
> > > A userspace VMM is supposed to get the details of the device's PASID
> > > capability
> > > and assemble a virtual PASID capability in a proper offset in the virtual
> PCI
> > > configuration space. While it is still an open on how to get the available
> > > offsets. Devices may have hidden bits that are not in the PCI cap chain.
> For
> > > now, there are two options to get the available offsets.[2]
> > >
> > > - Report the available offsets via ioctl. This requires device-specific logic
> > >   to provide available offsets. e.g., vfio-pci variant driver. Or may the
> device
> > >   provide the available offset by DVSEC.
> > > - Store the available offsets in a static table in userspace VMM. VMM gets
> the
> > >   empty offsets from this table.
> > >
> >
> > I'm not a fan of requesting a variant driver for every PASID-capable
> > VF just for the purpose of reporting a free range in the PCI config space.
> >
> > It's easier to do that quirk in userspace.
> >
> > But I like Alex's original comment that at least for PF there is no reason
> > to hide the offset. there could be a flag+field to communicate it. or
> > if there will be a new variant VF driver for other purposes e.g. migration
> > it can certainly fill the field too.
> 
> Yes, since this has been such a sticking point can we get a clean
> series that just enables it for PF and then come with a solution for
> VF?
> 

sure but we at least need to reach consensus on a minimal required
uapi covering both PF/VF to move forward so the user doesn't need
to touch different contracts for PF vs. VF.





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