Re: [PATCH] VFIO: remove dead notifier code

Anthony Krowiak
2026-04-08T14:35:00Z

On 4/7/26 1:59 PM, Paolo Bonzini wrote:
> 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>

There are two minor review comments about capitalization at the
beginning of
sentences in the vfio-ap.rst document in the Documentation/arch/s390
directory. Other than that:

Acked-by: Anthony Krowiak <akrowiak@linux.ibm.com>

> ---
> Documentation/arch/s390/vfio-ap.rst | 18 ++++++------------
> drivers/vfio/group.c | 3 ---
> drivers/vfio/vfio.h | 1 -
> drivers/vfio/vfio_iommu_type1.c | 1 -
> 4 files changed, 6 insertions(+), 17 deletions(-)
>
> diff --git a/Documentation/arch/s390/vfio-ap.rst b/Documentation/arch/s390/vfio-ap.rst
> index eba1991fbdba..2de0560bd70c 100644
> --- a/Documentation/arch/s390/vfio-ap.rst
> +++ b/Documentation/arch/s390/vfio-ap.rst
> @@ -431,17 +431,14 @@ 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

Capitalization:
s/the open_device callback/The open device callback/

> + 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.

Capitalization:
s/this callback/This callback/

>
> ioctl:
> this callback handles the VFIO_DEVICE_GET_INFO and VFIO_DEVICE_RESET ioctls
> @@ -449,9 +444,8 @@ matrix device.
>
> 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
> diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
> index 4f15016d2a5f..731dd0dead0d 100644
> --- a/drivers/vfio/group.c
> +++ b/drivers/vfio/group.c
> @@ -456,7 +456,6 @@ 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) {
> @@ -541,7 +540,6 @@ 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;
> }
> @@ -720,7 +718,6 @@ 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
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index 50128da18bca..0854f3fa1a22 100644
> --- a/drivers/vfio/vfio.h
> +++ b/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;
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 03cefdf99a4a..c8151ba54de3 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/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"