vfio: platform: support No-IOMMU mode

The vfio No-IOMMU mode was supported by this
'commit 03a76b60 ("vfio: Include No-IOMMU mode")',
but it only support vfio-pci.

Using vfio_iommu_group_get/put, but not iommu_group_get/put,
the platform devices can be exposed to userspace with
CONFIG_VFIO_NOIOMMU and the "enable_unsafe_noiommu_mode"
option enabled.

From 'commit 03a76b60 ("vfio: Include No-IOMMU mode")',
"This should make it very clear that this mode is not safe.
Additionally, CAP_SYS_RAWIO privileges are necessary to work
with groups and containers using this mode.  Groups making
use of this support are named /dev/vfio/noiommu-$GROUP and
can only make use of the special VFIO_NOIOMMU_IOMMU for the
container.  Use of this mode, specifically binding a device
without a native IOMMU group to a VFIO bus driver will taint
the kernel and should therefore not be considered supported."
Signed-off-by: Peng Fan <van.freenix@gmail.com>
Cc: Eric Auger <eric.auger@linaro.org>
Cc: Baptiste Reynal <b.reynal@virtualopensystems.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/platform/vfio_platform_common.c

@@ -561,7 +561,7 @@ int vfio_platform_probe_common(struct vfio_platform_device *vdev,
 
 	vdev->device = dev;
 
-	group = iommu_group_get(dev);
+	group = vfio_iommu_group_get(dev);
 	if (!group) {
 		pr_err("VFIO: No IOMMU group for device %s\n", vdev->name);
 		return -EINVAL;
@@ -569,7 +569,7 @@ int vfio_platform_probe_common(struct vfio_platform_device *vdev,
 
 	ret = vfio_add_group_dev(dev, &vfio_platform_ops, vdev);
 	if (ret) {
-		iommu_group_put(group);
+		vfio_iommu_group_put(group, dev);
 		return ret;
 	}
 
@@ -589,7 +589,7 @@ struct vfio_platform_device *vfio_platform_remove_common(struct device *dev)
 
 	if (vdev) {
 		vfio_platform_put_reset(vdev);
-		iommu_group_put(dev->iommu_group);
+		vfio_iommu_group_put(dev->iommu_group, dev);
 	}
 
 	return vdev;