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 <[email protected]>
> > > ---
> > > 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
> > >
