Re: 答复: [外部邮件] Re: [PATCH] virtio_ring: reset IN_ORDER state in virtqueue_init()

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

Eugenio, could you look at the qemu side of this pls?

On Fri, Sep 11, 2026 at 06:05:25AM +0000, Li,Rongqing wrote:
> > >
> > > The IN_ORDER feature uses additional software state to track the next
> > > available descriptor and in-flight descriptor batches.
> > >
> > > virtqueue_init() resets the common virtqueue state, but free_head and
> > > batch_last.id are initialized only when the virtqueue is created. When
> > > an IN_ORDER virtqueue is reset, these fields can retain state from the
> > > previous queue instance.
> > >
> > > Reset free_head and invalidate batch_last when initializing an
> > > IN_ORDER virtqueue. Keep this in virtqueue_init() so the state is
> > > initialized consistently for both newly created and reset virtqueues.
> > >
> > > Fixes: f6a15d854986 ("virtio_ring: add in order support")
> > 
> > I think this is needed for -stable.
> > 
> > > Signed-off-by: Li RongQing <lirongqing@baidu.com>
> > > ---
> > >  drivers/virtio/virtio_ring.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/drivers/virtio/virtio_ring.c
> > > b/drivers/virtio/virtio_ring.c index db678f5..d0dc464 100644
> > > --- a/drivers/virtio/virtio_ring.c
> > > +++ b/drivers/virtio/virtio_ring.c
> > > @@ -559,6 +559,11 @@ static void virtqueue_init(struct vring_virtqueue *vq,
> > u32 num)
> > >         vq->in_use = false;
> > >         vq->last_add_time_valid = false;  #endif
> > > +
> > > +       if (virtqueue_is_in_order(vq)) {
> > > +               vq->free_head = 0;
> > > +               vq->batch_last.id = UINT_MAX;
> > > +       }
> > 
> > I would try to reuse or refactor virtqueue_vring_attach_split() to reduce code
> > duplication.
> > 
> > Btw have you checked Qemu shadow virtqueue as it might suffer from the same
> > issue.
> > 
> 
> I checked QEMU's shadow virtqueue implementation. batch_last is reinitialized in vhost_svq_start(), 
> but free_head is not. Since the SVQ object can be reused across stop/start, free_head may retain stale 
> state. So a corresponding fix should be needed
> 
> void vhost_svq_start(VhostShadowVirtqueue *svq, VirtIODevice *vdev,
>                       VirtQueue *vq, VhostIOVATree *iova_tree)
>  {
>      ...
>      svq->shadow_avail_idx = 0;
>      svq->shadow_used_idx = 0;
> +    svq->free_head = 0;
>      memset(&svq->batch_last, 0, sizeof(svq->batch_last));
>      svq->last_used = 0;
>      svq->last_used_idx = 0;
> 
> thanks
>  
> [Li,Rongqing] 
> 
> 
> > Thanks
> > 
> > >  }
> > >
> > >
> > > --
> > > 2.9.4
> > >