Re: [PATCH V3 05/10] vfio: Allow null group for noiommu without containers

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Apr 02, 2026 at 10:11:41PM -0700, Jacob Pan wrote:

> @@ -598,6 +604,14 @@ static struct vfio_group *vfio_noiommu_group_alloc(struct device *dev,
>  	struct vfio_group *group;
>  	int ret;
>  
> +	/*
> +	 * With noiommu enabled under cdev interface only, there is no need to
> +	 * create a vfio_group if the group based containers are not enabled.
> +	 * The cdev interface is exclusively used for iommufd.
> +	 */
> +	if (vfio_null_group_allowed())
> +		return NULL;

Sashiko wondered if this causes a null pointer deref without pointing
at a specific case. Claude found a case:

@@ -696,6 +696,9 @@ void vfio_device_remove_group(struct vfio_device *device)
        struct vfio_group *group = device->group;
        struct iommu_group *iommu_group;
 
+       if (!group)
+               return;
+
        if (group->type == VFIO_NO_IOMMU || group->type == VFIO_EMULATED_IOMMU)
                iommu_group_remove_device(device->dev);

Happens during error unwind in __vfio_register_dev()

It also points out that the hunks are weirdly split between this patch
and "vfio: Enable cdev noiommu mode under iommufd" so that things are
broken at this point.

I think you should pull the vfio_device_has_group() and related into
this patch.

Jason