[Intel-gfx] [PATCH v5 17/19] vfio: Add VFIO_DEVICE_AT[DE]TACH_IOMMUFD_PT

[Jason Gunthorpe]

On Tue, Feb 28, 2023 at 01:36:24PM +0000, Liu, Yi L wrote:
> > From: Jason Gunthorpe <jgg at nvidia.com>
> > Sent: Tuesday, February 28, 2023 9:26 PM
> > 
> > On Tue, Feb 28, 2023 at 01:22:50PM +0000, Liu, Yi L wrote:
> > 
> > > > A null iommufd pointer and a bound df flag is sufficient to see that
> > > > it is compat mode.
> > >
> > > Hope df->is_cdev_device suits your expectation.:-) The code will look
> > > like below:
> > 
> > Yes, this is better.. However I'd suggest 'uses_container' as it is
> > clearer what the special case is
> 
> Surely doable. Need to add a helper like below:
> 
> bool vfio_device_group_uses_container()
> {
> 	lockdep_assert_held(&device->group->group_lock);
> 	return device->group->container;
> }

It should come from the df.

If you have a df then by definition:
  smp_load_acquire(..) == false     - Not bound
  df->device->iommufd_ctx != NULL   - Using iommufd
  df->group->containter != NULL     - Using legacy container
  all other cases                   - NO_IOMMU                

No locking required since all these cases after the smp_load_acquire
must be fixed for the lifetime of the df.

Jason