vfio: Add cdev for vfio_device

This adds cdev support for vfio_device. It allows the user to directly
open a vfio device w/o using the legacy container/group interface, as a
prerequisite for supporting new iommu features like nested translation
and etc.

The device fd opened in this manner doesn't have the capability to access
the device as the fops open() doesn't open the device until the successful
VFIO_DEVICE_BIND_IOMMUFD ioctl which will be added in a later patch.

With this patch, devices registered to vfio core would have both the legacy
group and the new device interfaces created.

- group interface : /dev/vfio/$groupID
- device interface: /dev/vfio/devices/vfioX - normal device
		    ("X" is a unique number across vfio devices)

For a given device, the user can identify the matching vfioX by searching
the vfio-dev folder under the sysfs path of the device. Take PCI device
(0000:6a:01.0) as an example, /sys/bus/pci/devices/0000\:6a\:01.0/vfio-dev/vfioX
implies the matching vfioX under /dev/vfio/devices/, and vfio-dev/vfioX/dev
contains the major:minor number of the matching /dev/vfio/devices/vfioX.
The user can get device fd by opening the /dev/vfio/devices/vfioX.

The vfio_device cdev logic in this patch:
*) __vfio_register_dev() path ends up doing cdev_device_add() for each
   vfio_device if VFIO_DEVICE_CDEV configured.
*) vfio_unregister_group_dev() path does cdev_device_del();

cdev interface does not support noiommu devices, so VFIO only creates the
legacy group interface for the physical devices that do not have IOMMU.
noiommu users should use the legacy group interface.

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>
Tested-by: Yanting Jiang <yanting.jiang@intel.com>
Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Tested-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Link: https://lore.kernel.org/r/20230718135551.6592-19-yi.l.liu@intel.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

1 files changed, 17 insertions, 4 deletions

diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 294bb5ecfc1c..8a9ebcc6980b 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -292,7 +292,7 @@ static int __vfio_register_dev(struct vfio_device *device,
 	if (ret)
 		return ret;
 
-	ret = device_add(&device->device);
+	ret = vfio_device_add(device);
 	if (ret)
 		goto err_out;
 
@@ -338,8 +338,11 @@ void vfio_unregister_group_dev(struct vfio_device *device)
 	 */
 	vfio_device_group_unregister(device);
 
-	/* Balances device_add in register path */
-	device_del(&device->device);
+	/*
+	 * Balances vfio_device_add() in register path, also prevents
+	 * new device opened by userspace in the cdev path.
+	 */
+	vfio_device_del(device);
 
 	vfio_device_put_registration(device);
 	rc = try_wait_for_completion(&device->comp);
@@ -567,7 +570,8 @@ static int vfio_device_fops_release(struct inode *inode, struct file *filep)
 	struct vfio_device_file *df = filep->private_data;
 	struct vfio_device *device = df->device;
 
-	vfio_df_group_close(df);
+	if (df->group)
+		vfio_df_group_close(df);
 
 	vfio_device_put_registration(device);
 
@@ -1216,6 +1220,7 @@ static int vfio_device_fops_mmap(struct file *filep, struct vm_area_struct *vma)
 
 const struct file_operations vfio_device_fops = {
 	.owner		= THIS_MODULE,
+	.open		= vfio_device_fops_cdev_open,
 	.release	= vfio_device_fops_release,
 	.read		= vfio_device_fops_read,
 	.write		= vfio_device_fops_write,
@@ -1567,9 +1572,16 @@ static int __init vfio_init(void)
 		goto err_dev_class;
 	}
 
+	ret = vfio_cdev_init(vfio.device_class);
+	if (ret)
+		goto err_alloc_dev_chrdev;
+
 	pr_info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
 	return 0;
 
+err_alloc_dev_chrdev:
+	class_destroy(vfio.device_class);
+	vfio.device_class = NULL;
 err_dev_class:
 	vfio_virqfd_exit();
 err_virqfd:
@@ -1580,6 +1592,7 @@ err_virqfd:
 static void __exit vfio_cleanup(void)
 {
 	ida_destroy(&vfio.device_ida);
+	vfio_cdev_cleanup();
 	class_destroy(vfio.device_class);
 	vfio.device_class = NULL;
 	vfio_virqfd_exit();