vfio: Test kvm pointer in _vfio_device_get_kvm_safe()

This saves some lines when adding the kvm get logic for the vfio_device
cdev path.

This also renames _vfio_device_get_kvm_safe() to be vfio_device_get_kvm_safe().
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Tested-by: Yanting Jiang <yanting.jiang@intel.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Link: https://lore.kernel.org/r/20230718135551.6592-20-yi.l.liu@intel.comSigned-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/group.c

@@ -160,12 +160,7 @@ static int vfio_group_ioctl_set_container(struct vfio_group *group,
 static void vfio_device_group_get_kvm_safe(struct vfio_device *device)
 {
 	spin_lock(&device->group->kvm_ref_lock);
-	if (!device->group->kvm)
-		goto unlock;
-
-	_vfio_device_get_kvm_safe(device, device->group->kvm);
-
-unlock:
+	vfio_device_get_kvm_safe(device, device->group->kvm);
 	spin_unlock(&device->group->kvm_ref_lock);
 }
 

drivers/vfio/vfio.h

@@ -340,10 +340,10 @@ enum { vfio_noiommu = false };
 #endif
 
 #ifdef CONFIG_HAVE_KVM
-void _vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm);
+void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm);
 void vfio_device_put_kvm(struct vfio_device *device);
 #else
-static inline void _vfio_device_get_kvm_safe(struct vfio_device *device,
+static inline void vfio_device_get_kvm_safe(struct vfio_device *device,
 					    struct kvm *kvm)
 {
 }

drivers/vfio/vfio_main.c

@@ -373,7 +373,7 @@ void vfio_unregister_group_dev(struct vfio_device *device)
 EXPORT_SYMBOL_GPL(vfio_unregister_group_dev);
 
 #ifdef CONFIG_HAVE_KVM
-void _vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm)
+void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm)
 {
 	void (*pfn)(struct kvm *kvm);
 	bool (*fn)(struct kvm *kvm);
@@ -381,6 +381,9 @@ void _vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm)
 
 	lockdep_assert_held(&device->dev_set->lock);
 
+	if (!kvm)
+		return;
+
 	pfn = symbol_get(kvm_put_kvm);
 	if (WARN_ON(!pfn))
 		return;