[PATCH v8 09/24] 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.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Terrence Xu <terrence.xu@intel.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
---
 drivers/vfio/group.c | 33 +++++++++++++++++++++++++++++++++
 drivers/vfio/vfio.h  |  3 +++
 2 files changed, 36 insertions(+)

diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
index 4f267ae7bebc..4de7a8fc3be1 100644
--- a/drivers/vfio/group.c
+++ b/drivers/vfio/group.c
@@ -383,6 +383,33 @@ static long vfio_group_fops_unl_ioctl(struct file *filep,
 	}
 }
 
+int vfio_device_block_group(struct vfio_device *device)
+{
+	struct vfio_group *group = device->group;
+	int ret = 0;
+
+	mutex_lock(&group->group_lock);
+	if (group->opened_file) {
+		ret = -EBUSY;
+		goto out_unlock;
+	}
+
+	group->cdev_device_open_cnt++;
+
+out_unlock:
+	mutex_unlock(&group->group_lock);
+	return ret;
+}
+
+void vfio_device_unblock_group(struct vfio_device *device)
+{
+	struct vfio_group *group = device->group;
+
+	mutex_lock(&group->group_lock);
+	group->cdev_device_open_cnt--;
+	mutex_unlock(&group->group_lock);
+}
+
 static int vfio_group_fops_open(struct inode *inode, struct file *filep)
 {
 	struct vfio_group *group =
@@ -405,6 +432,11 @@ 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.
 	 */
@@ -479,6 +511,7 @@ static void vfio_group_release(struct device *dev)
 	mutex_destroy(&group->device_lock);
 	mutex_destroy(&group->group_lock);
 	WARN_ON(group->iommu_group);
+	WARN_ON(group->cdev_device_open_cnt);
 	ida_free(&vfio.group_ida, MINOR(group->dev.devt));
 	kfree(group);
 }
diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
index 854f2c97cb9a..b2f20b78a707 100644
--- a/drivers/vfio/vfio.h
+++ b/drivers/vfio/vfio.h
@@ -83,8 +83,11 @@ 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_block_group(struct vfio_device *device);
+void vfio_device_unblock_group(struct vfio_device *device);
 int vfio_device_set_group(struct vfio_device *device,
 			  enum vfio_group_type type);
 void vfio_device_remove_group(struct vfio_device *device);
-- 
2.34.1