Re: [RFC 7/7] vfio: Add vfio_register_pasid_iommu_dev()

["Cao, Yahui" <yahui.cao@intel.com>]

On 10/9/2023 4:51 PM, Yi Liu wrote:
> From: Kevin Tian <kevin.tian@intel.com>
>
> This adds vfio_register_pasid_iommu_dev() for device driver to register
> virtual devices which are isolated per PASID in physical IOMMU. The major
> usage is for the SIOV devices which allows device driver to tag the DMAs
> out of virtual devices within it with different PASIDs.
>
> For a given vfio device, VFIO core creates both group user interface and
> device user interface (device cdev) if configured. However, for the virtual
> devices backed by PASID of the device, VFIO core shall only create device
> user interface as there is no plan to support such devices in the legacy
> vfio_iommu drivers which is a must if creating group user interface for
> such virtual devices. This introduces a VFIO_PASID_IOMMU group type for
> the device driver to register PASID virtual devices, and provides a wrapper
> API for it. In particular no iommu group (neither fake group or real group)
> exists per PASID, hence no group interface for this type.
>
> Signed-off-by: Kevin Tian <kevin.tian@intel.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
>
>   
> +/*
> + * Register a virtual device with IOMMU pasid protection. The user of
> + * this device can trigger DMA as long as all of its outgoing DMAs are
> + * always tagged with a pasid.
> + */
> +int vfio_register_pasid_iommu_dev(struct vfio_device *device)
> +{
> +	return __vfio_register_dev(device, VFIO_PASID_IOMMU);
> +}
> +

If CONFIG_VFIO_GROUP kconfig is selected, then there will be access to 
vdev->group shown as below
->__vfio_register_dev()
        ->vfio_device_add()
             ->vfio_device_is_noiommu() { return 
IS_ENABLED(CONFIG_VFIO_NOIOMMU) && vdev->group->type == VFIO_NO_IOMMU}

For SIOV virtual devices, vfio group is not created and vfio cdev is 
used. Thus vdev->group is NULL and there is NULL pointer access here.

Thanks.
Yahui.