[Intel-gfx] [PATCH v3 11/15] vfio: Add cdev_device_open_cnt to vfio_group

[Yi Liu <yi.l.liu@intel.com>]

for counting the devices that are opened via the cdev path. This count
is increased and decreased by the cdev path. The group path checks it
to achieve exclusion with the cdev path. With this, only one path (group
path or cdev path) will claim DMA ownership. This avoids scenarios in
which devices within the same group may be opened via different paths.

Signed-off-by: Yi Liu <yi.l.liu@intel.com>
---
 drivers/vfio/group.c | 5 +++++
 drivers/vfio/vfio.h  | 1 +
 2 files changed, 6 insertions(+)

diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
index 9f3f6f0e4942..f3f5f4589cdd 100644
--- a/drivers/vfio/group.c
+++ b/drivers/vfio/group.c
@@ -403,6 +403,11 @@ static int vfio_group_fops_open(struct inode *inode, struct file *filep)
 		goto out_unlock;
 	}
 
+	if (group->cdev_device_open_cnt) {
+		ret = -EBUSY;
+		goto out_unlock;
+	}
+
 	/*
 	 * Do we need multiple instances of the group open?  Seems not.
 	 */
diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
index 6f063e31d08a..7a77fb12bd2c 100644
--- a/drivers/vfio/vfio.h
+++ b/drivers/vfio/vfio.h
@@ -84,6 +84,7 @@ struct vfio_group {
 	struct blocking_notifier_head	notifier;
 	struct iommufd_ctx		*iommufd;
 	spinlock_t			kvm_ref_lock;
+	unsigned int			cdev_device_open_cnt;
 };
 
 int vfio_device_set_group(struct vfio_device *device,
-- 
2.34.1