[PATCH V2 05/11] vfio: Allow null group for noiommu without containers

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

In case of noiommu mode is enabled for VFIO cdev without VFIO container
nor IOMMUFD provided compatibility container, there is no need to
create a dummy group. Update the group operations to tolerate null group
pointer.

Signed-off-by: Jacob Pan <jacob.pan@linux.microsoft.com>
---
 drivers/vfio/group.c | 14 ++++++++++++++
 drivers/vfio/vfio.h  | 17 +++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
index 4f15016d2a5f..98f2a4f2ebff 100644
--- a/drivers/vfio/group.c
+++ b/drivers/vfio/group.c
@@ -381,6 +381,9 @@ int vfio_device_block_group(struct vfio_device *device)
 	struct vfio_group *group = device->group;
 	int ret = 0;
 
+	if (vfio_null_group_allowed() && !group)
+		return 0;
+
 	mutex_lock(&group->group_lock);
 	if (group->opened_file) {
 		ret = -EBUSY;
@@ -398,6 +401,9 @@ void vfio_device_unblock_group(struct vfio_device *device)
 {
 	struct vfio_group *group = device->group;
 
+	if (vfio_null_group_allowed() && !group)
+		return;
+
 	mutex_lock(&group->group_lock);
 	group->cdev_device_open_cnt--;
 	mutex_unlock(&group->group_lock);
@@ -589,6 +595,14 @@ 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;
+
 	iommu_group = iommu_group_alloc();
 	if (IS_ERR(iommu_group))
 		return ERR_CAST(iommu_group);
diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
index 50128da18bca..838c08077ce2 100644
--- a/drivers/vfio/vfio.h
+++ b/drivers/vfio/vfio.h
@@ -113,6 +113,18 @@ bool vfio_device_has_container(struct vfio_device *device);
 int __init vfio_group_init(void);
 void vfio_group_cleanup(void);
 
+/*
+ * 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;
+}
+
 static inline bool vfio_device_is_noiommu(struct vfio_device *vdev)
 {
 	return IS_ENABLED(CONFIG_VFIO_NOIOMMU) &&
@@ -189,6 +201,11 @@ static inline void vfio_group_cleanup(void)
 {
 }
 
+static inline bool vfio_null_group_allowed(void)
+{
+	return false;
+}
+
 static inline bool vfio_device_is_noiommu(struct vfio_device *vdev)
 {
 	return false;
-- 
2.34.1