Re: [PATCH V4 05/10] vfio: Allow null group for noiommu without containers

[Jacob Pan <jacob.pan@linux.microsoft.com>]

Hi Kevin,

On Thu, 16 Apr 2026 08:13:22 +0000
"Tian, Kevin" <kevin.tian@intel.com> wrote:

> > From: Jacob Pan <jacob.pan@linux.microsoft.com>
> > Sent: Wednesday, April 15, 2026 5:14 AM
> > 
> > +/*
> > + * With noiommu enabled and no containers are supported, allow
> > devices that
> > + * don't have a dummy group.
> > + */
> > +static inline bool vfio_null_group_allowed(void)
> > +{
> > +	if (vfio_noiommu && (!IS_ENABLED(CONFIG_VFIO_CONTAINER)
> > && !IS_ENABLED(CONFIG_IOMMUFD_VFIO_CONTAINER)))
> > +		return true;
> > +
> > +	return false;
> > +}  
> 
> 'allow' kind of implies a policy choice, but throughput this patch
> it's actually a mandatory state when those conditions are true. Can we
> strengthen the words here and other places to not given an impression
> that even when null group is allowed it's still possible to create a
> vfio group for that situation?
> 
> Just like another comment said, iommufd is the only choice in this
> case, then probably could call it vfio_has_iommufd_group()?
Indeed this condition is not an option. I am ok with either
vfio_has_iommufd_group() or directly name what is being checked
vfio_noiommu_no_container()

> > 
> > @@ -392,6 +396,16 @@ void vfio_unregister_group_dev(struct
> > vfio_device *device)
> >  	bool interrupted = false;
> >  	long rc;
> > 
> > +	/*
> > +	 * For noiommu devices without a container, thus no dummy
> > group,
> > +	 * simply delete and unregister to balance refcount.
> > +	 */
> > +	if (!vfio_device_has_group(device)) {
> > +		vfio_device_del(device);
> > +		vfio_device_put_registration(device);
> > +		return;
> > +	}
> > +
> >  	/*  
> 
> can you elaborate why the following wait loop is also skipped? then
> above is removed by patch7 later...
My mistake, will delete this from both patches.

Thanks for catching this.

Jacob