Re: [PATCH v9 3/6] iommufd: Allow binding to a noiommu device

[Pranjal Shrivastava <praan@google.com>]

On Thu, Jun 11, 2026 at 10:26:55AM -0700, Jacob Pan wrote:
> From: Jason Gunthorpe <jgg@nvidia.com>
> 
> Allow iommufd to bind devices without an IOMMU (noiommu mode) by creating
> a dummy igroup for such devices and skipping hwpt operations.
> 
> This enables noiommu devices to operate through the same iommufd API as IOMMU-
> capable devices.
> 
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Yi Liu <yi.l.liu@intel.com>
> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Jacob Pan <jacob.pan@linux.microsoft.com>

[...]

> +/*
> + * Detect a noiommu device for the cdev path. We check dev->iommu rather than
> + * using device_iommu_mapped() (which checks dev->iommu_group) because when
> + * both group and cdev interfaces coexist, the group path assigns a fake
> + * noiommu iommu_group to the device. That would cause device_iommu_mapped()
> + * to return true and hide the noiommu case from the cdev path. dev->iommu is
> + * reliably NULL when no IOMMU driver is managing the device.
> + */
> +static bool iommufd_device_is_noiommu(struct iommufd_device *idev)
> +{
> +	return IS_ENABLED(CONFIG_IOMMUFD_NOIOMMU) && !idev->dev->iommu;
> +}
> +

Helpful comment! Thanks :)

>  static void iommufd_group_release(struct kref *kref)
>  {
>  	struct iommufd_group *igroup =
> @@ -30,9 +43,11 @@ static void iommufd_group_release(struct kref *kref)
>  
>  	WARN_ON(!xa_empty(&igroup->pasid_attach));
>  
> -	xa_cmpxchg(&igroup->ictx->groups, iommu_group_id(igroup->group), igroup,
> -		   NULL, GFP_KERNEL);
> -	iommu_group_put(igroup->group);
> +	if (igroup->group) {
> +		xa_cmpxchg(&igroup->ictx->groups, iommu_group_id(igroup->group),
> +			   igroup, NULL, GFP_KERNEL);
> +		iommu_group_put(igroup->group);
> +	}
>  	mutex_destroy(&igroup->lock);
>  	kfree(igroup);
>  }

Reviewed-by: Pranjal Shrivastava <praan@google.com>

Thanks,
Praan