Re: [PATCH v3 10/15] vhost-net: vhost-kernel: introduce vhost_net_virtqueue_reset()

[Jason Wang]

On Mon, Sep 5, 2022 at 6:15 PM Kangjie Xu <kangjie.xu@linux.alibaba.com> wrote:
>
>
> 在 2022/9/5 16:03, Jason Wang 写道:
> >
> > 在 2022/8/25 16:08, Kangjie Xu 写道:
> >> Introduce vhost_virtqueue_reset(), which can reset the specific
> >> virtqueue in the device. Then it will unmap vrings and the desc
> >> of the virtqueue.
> >>
> >> Here we do not reuse the vhost_net_stop_one() or vhost_dev_stop(),
> >> because they work at queue pair level. We do not use
> >> vhost_virtqueue_stop() because it may stop the device in the
> >> backend.
> >
> >
> > So I think this is not true at least for vhost-net kernel baceknd.
> >
> >
> But vhost-user(OVS-DPDK) will stop the device.

Yes, what I meant is that, considering this series only deal with
vhost-net. We can leave any "fix" or "workaround" until e.g the
vhost-user support is posted?

>
> When DPDK vhost received VHOST_USER_GET_VRING_BASE message, it will call
> vhost_destroy_device_notify() to destroy the device.

Right, actually this trick is used even in some hardware.

>
> It seems like it is a inconsistency error in DPDK. Maybe I should submit
> a patch to DPDK. We can stop the device only when all the virtqueues in
> one device are destroyed.

That would be fine.

>
> >>
> >> This patch only considers the case of vhost-kernel, when
> >> NetClientDriver is NET_CLIENT_DRIVER_TAP.
> >>
> >> Signed-off-by: Kangjie Xu <kangjie.xu@linux.alibaba.com>
> >> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> >> ---
> >>   hw/net/vhost_net.c      | 22 ++++++++++++++++++++++
> >>   include/net/vhost_net.h |  2 ++
> >>   2 files changed, 24 insertions(+)
> >>
> >> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> >> index ccac5b7a64..be51be98b3 100644
> >> --- a/hw/net/vhost_net.c
> >> +++ b/hw/net/vhost_net.c
> >> @@ -514,3 +514,25 @@ int vhost_net_set_mtu(struct vhost_net *net,
> >> uint16_t mtu)
> >>         return vhost_ops->vhost_net_set_mtu(&net->dev, mtu);
> >>   }
> >> +
> >> +void vhost_net_virtqueue_reset(VirtIODevice *vdev, NetClientState *nc,
> >> +                               int vq_index)
> >> +{
> >> +    VHostNetState *net = get_vhost_net(nc->peer);
> >> +    const VhostOps *vhost_ops = net->dev.vhost_ops;
> >> +    struct vhost_vring_file file = { .fd = -1 };
> >> +    int idx;
> >> +
> >> +    /* should only be called after backend is connected */
> >> +    assert(vhost_ops);
> >> +
> >> +    idx = vhost_ops->vhost_get_vq_index(&net->dev, vq_index);
> >> +
> >> +    if (net->nc->info->type == NET_CLIENT_DRIVER_TAP) {
> >> +        file.index = idx;
> >> +        int r = vhost_net_set_backend(&net->dev, &file);
> >> +        assert(r >= 0);
> >> +    }
> >
> >
> > Do we need to reset e.g last_avail_idx here?
> >
> > Thanks
> >
> I did not reset it because we will re-configure them when we restart
> virtqueue.

Is last_avail_idx reset to 0 in this case?

Thanks

>
> Thanks
>
> >
> >> +
> >> +    vhost_virtqueue_unmap(&net->dev, vdev, net->dev.vqs + idx, idx);
> >> +}
> >> diff --git a/include/net/vhost_net.h b/include/net/vhost_net.h
> >> index 387e913e4e..85d85a4957 100644
> >> --- a/include/net/vhost_net.h
> >> +++ b/include/net/vhost_net.h
> >> @@ -48,4 +48,6 @@ uint64_t vhost_net_get_acked_features(VHostNetState
> >> *net);
> >>     int vhost_net_set_mtu(struct vhost_net *net, uint16_t mtu);
> >>   +void vhost_net_virtqueue_reset(VirtIODevice *vdev, NetClientState
> >> *nc,
> >> +                               int vq_index);
> >>   #endif
>