Re: [PATCH v2 1/2] vhost-user: fix VirtQ notifier cleanup

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Sep 17, 2021 at 08:26:15PM +0800, Xueming Li wrote:
> When vhost-user device stop and unmmap notifier address, vCPU thread
> that writing the notifier via old flatview failed with accessing invalid
> address.
> 
> To avoid this concurrent issue, wait memory flatview update by draining
> rcu callbacks before unmaping notifiers.
> 
> Fixes: 44866521bd6e ("vhost-user: support registering external host notifiers")
> Cc: tiwei.bie@intel.com
> Cc: qemu-stable@nongnu.org
> Cc: Yuwei Zhang <zhangyuwei.9149@bytedance.com>
> Signed-off-by: Xueming Li <xuemingl@nvidia.com>


Pls post v2 as a new thread, with changelog in the cover letter.

> ---
>  hw/virtio/vhost-user.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 2c8556237f..08581e6711 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -1165,6 +1165,11 @@ static void vhost_user_host_notifier_remove(struct vhost_dev *dev,
>  
>      if (n->addr && n->set) {
>          virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, false);
> +        if (!qemu_in_vcpu_thread())
> +            /* Wait vCPU threads accessing notifier via old flatview. */

Wait VM - Wait for VM

> +            drain_call_rcu();

okay.
but this has a coding style violation:
should use {} in if.


> +        munmap(n->addr, qemu_real_host_page_size);
> +        n->addr = NULL;
>          n->set = false;
>      }
>  }
> @@ -1502,12 +1507,7 @@ static int vhost_user_slave_handle_vring_host_notifier(struct vhost_dev *dev,
>  
>      n = &user->notifier[queue_idx];
>  
> -    if (n->addr) {
> -        virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, false);
> -        object_unparent(OBJECT(&n->mr));
> -        munmap(n->addr, page_size);
> -        n->addr = NULL;
> -    }
> +    vhost_user_host_notifier_remove(dev, queue_idx);
>  
>      if (area->u64 & VHOST_USER_VRING_NOFD_MASK) {
>          return 0;
> @@ -2484,11 +2484,17 @@ void vhost_user_cleanup(VhostUserState *user)
>      for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
>          if (user->notifier[i].addr) {
>              object_unparent(OBJECT(&user->notifier[i].mr));
> +        }
> +    }
> +    memory_region_transaction_commit();
> +    /* Wait VM threads accessing old flatview which contains notifier. */

Wait VM - Wait for VM

> +    drain_call_rcu();
> +    for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
> +        if (user->notifier[i].addr) {
>              munmap(user->notifier[i].addr, qemu_real_host_page_size);
>              user->notifier[i].addr = NULL;
>          }
>      }
> -    memory_region_transaction_commit();
>      user->chr = NULL;
>  }
>  
> -- 
> 2.33.0