vfio: Remove vfio_external_group_match_file()

vfio_group_fops_open() ensures there is only ever one struct file open for
any struct vfio_group at any time:

	/* Do we need multiple instances of the group open?  Seems not. */
	opened = atomic_cmpxchg(&group->opened, 0, 1);
	if (opened) {
		vfio_group_put(group);
		return -EBUSY;

Therefor the struct file * can be used directly to search the list of VFIO
groups that KVM keeps instead of using the
vfio_external_group_match_file() callback to try to figure out if the
passed in FD matches the list or not.

Delete vfio_external_group_match_file().

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/4-v3-f7729924a7ea+25e33-vfio_kvm_no_group_jgg@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio.c

@@ -1685,15 +1685,6 @@ void vfio_group_put_external_user(struct vfio_group *group)
 }
 EXPORT_SYMBOL_GPL(vfio_group_put_external_user);
 
-bool vfio_external_group_match_file(struct vfio_group *test_group,
-				    struct file *filep)
-{
-	struct vfio_group *group = filep->private_data;
-
-	return (filep->f_op == &vfio_group_fops) && (group == test_group);
-}
-EXPORT_SYMBOL_GPL(vfio_external_group_match_file);
-
 /**
  * vfio_file_iommu_group - Return the struct iommu_group for the vfio group file
  * @file: VFIO group file

include/linux/vfio.h

@@ -138,8 +138,6 @@ int vfio_mig_get_next_state(struct vfio_device *device,
  */
 extern struct vfio_group *vfio_group_get_external_user(struct file *filep);
 extern void vfio_group_put_external_user(struct vfio_group *group);
-extern bool vfio_external_group_match_file(struct vfio_group *group,
-					   struct file *filep);
 extern struct iommu_group *vfio_file_iommu_group(struct file *file);
 extern long vfio_external_check_extension(struct vfio_group *group,
 					  unsigned long arg);

virt/kvm/vfio.c

@@ -49,22 +49,6 @@ static struct vfio_group *kvm_vfio_group_get_external_user(struct file *filep)
 	return vfio_group;
 }
 
-static bool kvm_vfio_external_group_match_file(struct vfio_group *group,
-					       struct file *filep)
-{
-	bool ret, (*fn)(struct vfio_group *, struct file *);
-
-	fn = symbol_get(vfio_external_group_match_file);
-	if (!fn)
-		return false;
-
-	ret = fn(group, filep);
-
-	symbol_put(vfio_external_group_match_file);
-
-	return ret;
-}
-
 static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
 {
 	void (*fn)(struct vfio_group *);
@@ -239,8 +223,7 @@ static int kvm_vfio_group_del(struct kvm_device *dev, unsigned int fd)
 	mutex_lock(&kv->lock);
 
 	list_for_each_entry(kvg, &kv->group_list, node) {
-		if (!kvm_vfio_external_group_match_file(kvg->vfio_group,
-							f.file))
+		if (kvg->file != f.file)
 			continue;
 
 		list_del(&kvg->node);