Re: [PATCH v5 17/19] vfio: Add VFIO_DEVICE_AT[DE]TACH_IOMMUFD_PT

Jason Gunthorpe
2023-02-28T13:43:51Z

On Tue, Feb 28, 2023 at 01:36:24PM +0000, Liu, Yi L wrote:
> > From: Jason Gunthorpe <jgg@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