Re: [PATCH v6 1/2] vhost-user: remove VirtQ notifier restore

[Xueming(Steven) Li]

On Mon, 2021-11-01 at 17:06 -0400, Michael S. Tsirkin wrote:
> On Mon, Nov 01, 2021 at 04:38:12PM +0800, Xueming Li wrote:
> > When vhost-user vdpa client suspend, backend may close all resources,
> > VQ notifier mmap address become invalid, restore MR which contains
> > the invalid address is wrong. vdpa client will set VQ notifier after
> > reconnect.
> > 
> > This patch removes VQ notifier restore and related flags to avoid reusing
> > invalid address.
> > 
> > Fixes: 44866521bd6e ("vhost-user: support registering external host 
> > notifiers")
> > Cc: qemu-stable@nongnu.org
> > Cc: Yuwei Zhang <zhangyuwei.9149@bytedance.com>
> > Signed-off-by: Xueming Li <xuemingl@nvidia.com>
> > ---
> >  hw/virtio/vhost-user.c         | 19 +------------------
> >  include/hw/virtio/vhost-user.h |  1 -
> >  2 files changed, 1 insertion(+), 19 deletions(-)
> > 
> > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> > index bf6e50223c..c671719e9b 100644
> > --- a/hw/virtio/vhost-user.c
> > +++ b/hw/virtio/vhost-user.c
> > @@ -1143,19 +1143,6 @@ static int vhost_user_set_vring_num(struct vhost_dev 
> > *dev,
> >      return vhost_set_vring(dev, VHOST_USER_SET_VRING_NUM, ring);
> >  }
> >  
> > -static void vhost_user_host_notifier_restore(struct vhost_dev *dev,
> > -                                             int queue_idx)
> > -{
> > -    struct vhost_user *u = dev->opaque;
> > -    VhostUserHostNotifier *n = &u->user->notifier[queue_idx];
> > -    VirtIODevice *vdev = dev->vdev;
> > -
> > -    if (n->addr && !n->set) {
> > -        virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, true);
> > -        n->set = true;
> > -    }
> > -}
> > -
> >  static void vhost_user_host_notifier_remove(struct vhost_dev *dev,
> >                                              int queue_idx)
> >  {
> > @@ -1163,17 +1150,14 @@ static void vhost_user_host_notifier_remove(struct 
> > vhost_dev *dev,
> >      VhostUserHostNotifier *n = &u->user->notifier[queue_idx];
> >      VirtIODevice *vdev = dev->vdev;
> >  
> > -    if (n->addr && n->set) {
> > +    if (n->addr) {
> >          virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, false);
> > -        n->set = false;
> >      }
> >  }
> > 
> 
> So on vq stop we still remove the notifier...
>   
> >  static int vhost_user_set_vring_base(struct vhost_dev *dev,
> >                                       struct vhost_vring_state *ring)
> >  {
> > -    vhost_user_host_notifier_restore(dev, ring->index);
> > -
> >      return vhost_set_vring(dev, VHOST_USER_SET_VRING_BASE, ring);
> >  }
> >  
> 
> but on vq start we do not reinstate it? Does this not mean that
> notifiers won't work after stop then start?


Yes, backend initially work w/o host notifier, request VM driver to
install notifier if needed - call this function through slave socket.

> 
> 
> > @@ -1538,7 +1522,6 @@ static int 
> > vhost_user_slave_handle_vring_host_notifier(struct vhost_dev *dev,
> >      }
> >  
> >      n->addr = addr;
> > -    n->set = true;
> >  
> >      return 0;
> >  }
> > diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h
> > index a9abca3288..f6012b2078 100644
> > --- a/include/hw/virtio/vhost-user.h
> > +++ b/include/hw/virtio/vhost-user.h
> > @@ -14,7 +14,6 @@
> >  typedef struct VhostUserHostNotifier {
> >      MemoryRegion mr;
> >      void *addr;
> > -    bool set;
> >  } VhostUserHostNotifier;
> >  
> >  typedef struct VhostUserState {
> > -- 
> > 2.33.0
>