vfio: remove dead notifier code

group->notifier is dead code. VFIO initializes it and checks it for
emptiness on teardown, but nobody ever registers on it or triggers it.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Anthony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20260407175934.1602711-1-pbonzini@redhat.com
Signed-off-by: Alex Williamson <alex@shazbot.org>

Author: bonzini

Documentation/arch/s390/vfio-ap.rst

@@ -431,27 +431,23 @@ matrix device.
 * callback interfaces
 
   open_device:
-    The vfio_ap driver uses this callback to register a
-    VFIO_GROUP_NOTIFY_SET_KVM notifier callback function for the matrix mdev
-    devices. The open_device callback is invoked by userspace to connect the
-    VFIO iommu group for the matrix mdev device to the MDEV bus. Access to the
-    KVM structure used to configure the KVM guest is provided via this callback.
-    The KVM structure, is used to configure the guest's access to the AP matrix
-    defined via the vfio_ap mediated device's sysfs attribute files.
+    the open_device callback is invoked by userspace to connect the
+    VFIO iommu group for the matrix mdev device to the MDEV bus.  The
+    callback retrieves the KVM structure used to configure the KVM guest
+    and configures the guest's access to the AP matrix defined via the
+    vfio_ap mediated device's sysfs attribute files.
 
   close_device:
-    unregisters the VFIO_GROUP_NOTIFY_SET_KVM notifier callback function for the
-    matrix mdev device and deconfigures the guest's AP matrix.
+    this callback deconfigures the guest's AP matrix.
 
   ioctl:
     this callback handles the VFIO_DEVICE_GET_INFO and VFIO_DEVICE_RESET ioctls
     defined by the vfio framework.
 
 Configure the guest's AP resources
 ----------------------------------
-Configuring the AP resources for a KVM guest will be performed when the
-VFIO_GROUP_NOTIFY_SET_KVM notifier callback is invoked. The notifier
-function is called when userspace connects to KVM. The guest's AP resources are
+Configuring the AP resources for a KVM guest will be performed at the
+time of ``open_device`` and ``close_device``. The guest's AP resources are
 configured via its APCB by:
 
 * Setting the bits in the APM corresponding to the APIDs assigned to the

drivers/vfio/group.c

@@ -461,7 +461,6 @@ static int vfio_group_fops_release(struct inode *inode, struct file *filep)
 	 * Device FDs hold a group file reference, therefore the group release
 	 * is only called when there are no open devices.
 	 */
-	WARN_ON(group->notifier.head);
 	if (group->container)
 		vfio_group_detach_container(group);
 	if (group->iommufd) {
@@ -546,7 +545,6 @@ static struct vfio_group *vfio_group_alloc(struct iommu_group *iommu_group,
 	/* put in vfio_group_release() */
 	iommu_group_ref_get(iommu_group);
 	group->type = type;
-	BLOCKING_INIT_NOTIFIER_HEAD(&group->notifier);
 
 	return group;
 }
@@ -725,7 +723,6 @@ void vfio_device_remove_group(struct vfio_device *device)
 	 * properly hold the group reference.
 	 */
 	WARN_ON(!list_empty(&group->device_list));
-	WARN_ON(group->notifier.head);
 
 	/*
 	 * Revoke all users of group->iommu_group. At this point we know there

drivers/vfio/vfio.h

@@ -90,7 +90,6 @@ struct vfio_group {
 	struct mutex			group_lock;
 	struct kvm			*kvm;
 	struct file			*opened_file;
-	struct blocking_notifier_head	notifier;
 	struct iommufd_ctx		*iommufd;
 	spinlock_t			kvm_ref_lock;
 	unsigned int			cdev_device_open_cnt;

drivers/vfio/vfio_iommu_type1.c

@@ -36,7 +36,6 @@
 #include <linux/uaccess.h>
 #include <linux/vfio.h>
 #include <linux/workqueue.h>
-#include <linux/notifier.h>
 #include <linux/mm_inline.h>
 #include <linux/overflow.h>
 #include "vfio.h"