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

["Li,Rongqing" <lirongqing@baidu.com>]

> >
> > 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
> >