[Intel-gfx] [PATCH v3 12/12] vfio/pci: Report dev_id in VFIO_DEVICE_GET_PCI_HOT_RESET_INFO

[Liu, Yi L]

> From: Jason Gunthorpe <jgg at nvidia.com>
> Sent: Thursday, April 13, 2023 7:51 PM
> 
> On Thu, Apr 13, 2023 at 08:25:52AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg at nvidia.com>
> > > Sent: Thursday, April 13, 2023 4:07 AM
> > >
> > >
> > > > in which case we need c) a way to
> > > > report the overall set of affected devices regardless of ownership in
> > > > support of 4), BDF?
> > >
> > > Yes, continue to use INFO unmodified.
> > >
> > > > Are we back to replacing group-ids with dev-ids in the INFO structure,
> > > > where an invalid dev-id either indicates an affected device with
> > > > implied ownership (ok) or a gap in ownership (bad) and a flag somewhere
> > > > is meant to indicate the overall disposition based on the availability
> > > > of reset?
> > >
> > > As you explore in the following this gets ugly. I prefer to keep INFO
> > > unchanged and add INFO2.
> > >
> >
> > INFO needs a change when VFIO_GROUP is disabled. Now it assumes
> > a valid iommu group always exists:
> >
> > vfio_pci_fill_devs()
> > {
> > 	...
> > 	iommu_group = iommu_group_get(&pdev->dev);
> > 	if (!iommu_group)
> > 		return -EPERM; /* Cannot reset non-isolated devices */
> > 	...
> > }
> 
> This can still work in a ugly way. With a INFO2 the only purpose of
> INFO would be debugging, so if someone uses no-iommu, with hotreset
> and misconfigures it then the only downside is they don't get the
> debugging print. But we know of nothing that uses this combination
> anyhow..

Today, at least QEMU will not go to do hot-reset if _INFO fails. I think
this check may need to be relaxed if want _INFO work when there is
no VFIO_GROUP (also no fake iommu_group).

Regards,
Yi Liu