Re: [Intel-gfx] [PATCH v6 12/24] vfio/pci: Allow passing zero-length fd array in VFIO_DEVICE_PCI_HOT_RESET

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Mar 22, 2023 at 08:17:54AM +0000, Liu, Yi L wrote:

> Could you elaborate what is required with _INFO before libvirt can
> use a FD pass?

Make a new _INFO that returns an array of dev_ids within the cdev's
iommufd_ctx that are part of the reset group, eg the devset.

qemu will call this for each dev_id after it opens the cdev to
generate the groupings.

> > But for the current qemu setup it will open cdev directly and it will
> > know the BDF so it can still use the current _INFO.
> > 
> > Though it would be nice if qemu didn't need two implementations so Yi
> > I'd rather see a new info in this series as well and qemu can just
> > consistently use dev_id and never bdf in iommufd mode.
> 
> I have one concern here. iommufd dev_id is not a static info as much as
> bdf. It is generated when bound to iommufd. So if there are devices that
> are affected but not bound to iommufd yet at the time of invoking _INFO,
> then the _INFO ioctl just gets a subset of the affected devices. Is it enough?

I'd probably use similar logic as the reset path, if one of reset
group devices is open and on a different iommufd_ctx then fail the
IOCTL with EPERM.

Jason