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

[Liu, Yi L]

Hi Alex,

> From: Alex Williamson <alex.williamson at redhat.com>
> Sent: Monday, April 3, 2023 11:02 PM
> 
> On Mon, 3 Apr 2023 09:25:06 +0000
> "Liu, Yi L" <yi.l.liu at intel.com> wrote:
> 
> > > From: Liu, Yi L <yi.l.liu at intel.com>
> > > Sent: Saturday, April 1, 2023 10:44 PM
> >
> > > @@ -791,7 +813,21 @@ static int vfio_pci_fill_devs(struct pci_dev *pdev, void
> *data)
> > >  	if (!iommu_group)
> > >  		return -EPERM; /* Cannot reset non-isolated devices */
> >
> > Hi Alex,
> >
> > Is disabling iommu a sane way to test vfio noiommu mode?
> 
> Yes
> 
> > I added intel_iommu=off to disable intel iommu and bind a device to vfio-pci.
> > I can see the /dev/vfio/noiommu-0 and /dev/vfio/devices/noiommu-vfio0. Bind
> > iommufd==-1 can succeed, but failed to get hot reset info due to the above
> > group check. Reason is that this happens to have some affected devices, and
> > these devices have no valid iommu_group (because they are not bound to vfio-pci
> > hence nobody allocates noiommu group for them). So when hot reset info loops
> > such devices, it failed with -EPERM. Is this expected?
> 
> Hmm, I didn't recall that we put in such a limitation, but given the
> minimally intrusive approach to no-iommu and the fact that we never
> defined an invalid group ID to return to the user, it makes sense that
> we just blocked the ioctl for no-iommu use.  I guess we can do the same
> for no-iommu cdev.

I just realize a further issue related to this limitation. Remember that we
may finally compile out the vfio group infrastructure in the future. Say I
want to test noiommu, I may boot such a kernel with iommu disabled. I think
the _INFO ioctl would fail as there is no iommu_group. Does it mean we will
not support hot reset for noiommu in future if vfio group infrastructure is
compiled out?

As another thread, we are going to add a new bdf/group capability to
DEVICE_GET_INFO. If the above kernel is booted, shall we exclude the new
bdf/group capability or add a flag in the capability to mark the group_id
is invalid?

Regards,
Yi Liu