Re: [Qemu-devel] [RFC v2 8/8] virtio: guest driver reload for vhost-net

[Wei Xu <wexu@redhat.com>]

On Wed, Jun 06, 2018 at 11:48:19AM +0800, Jason Wang wrote:
> 
> 
> On 2018年06月06日 03:08, wexu@redhat.com wrote:
> >From: Wei Xu <wexu@redhat.com>
> >
> >last_avail, avail_wrap_count, used_idx and used_wrap_count are
> >needed to support vhost-net backend, all these are either 16 or
> >bool variables, since state.num is 64bit wide, so here it is
> >possible to put them to the 'num' without introducing a new case
> >while handling ioctl.
> >
> >Unload/Reload test has been done successfully with a patch in vhost kernel.
> 
> You need a patch to enable vhost.
> 
> And I think you can only do it for vhost-kenrel now since vhost-user
> protocol needs some extension I believe.

OK.

> 
> >
> >Signed-off-by: Wei Xu <wexu@redhat.com>
> >---
> >  hw/virtio/virtio.c | 42 ++++++++++++++++++++++++++++++++++--------
> >  1 file changed, 34 insertions(+), 8 deletions(-)
> >
> >diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> >index 4543974..153f6d7 100644
> >--- a/hw/virtio/virtio.c
> >+++ b/hw/virtio/virtio.c
> >@@ -2862,33 +2862,59 @@ hwaddr virtio_queue_get_used_size(VirtIODevice *vdev, int n)
> >      }
> >  }
> >-uint16_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n)
> >+uint64_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n)
> >  {
> >-    return vdev->vq[n].last_avail_idx;
> >+    uint64_t num;
> >+
> >+    num = vdev->vq[n].last_avail_idx;
> >+    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> >+        num |= ((uint64_t)vdev->vq[n].avail_wrap_counter) << 16;
> >+        num |= ((uint64_t)vdev->vq[n].used_idx) << 32;
> >+        num |= ((uint64_t)vdev->vq[n].used_wrap_counter) << 48;
> 
> So s.num is 32bit, I don't think this can even work.

I mistakenly checked out s.num is 64bit, will add a new case in next version.

Wei

> 
> Thanks
> 
> >+    }
> >+
> >+    return num;
> >  }
> >-void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint16_t idx)
> >+void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint64_t num)
> >  {
> >-    vdev->vq[n].last_avail_idx = idx;
> >-    vdev->vq[n].shadow_avail_idx = idx;
> >+    vdev->vq[n].shadow_avail_idx = vdev->vq[n].last_avail_idx = (uint16_t)(num);
> >+
> >+    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> >+        vdev->vq[n].avail_wrap_counter = (uint16_t)(num >> 16);
> >+        vdev->vq[n].used_idx = (uint16_t)(num >> 32);
> >+        vdev->vq[n].used_wrap_counter = (uint16_t)(num >> 48);
> >+    }
> >  }
> >  void virtio_queue_restore_last_avail_idx(VirtIODevice *vdev, int n)
> >  {
> >      rcu_read_lock();
> >-    if (vdev->vq[n].vring.desc) {
> >+    if (!vdev->vq[n].vring.desc) {
> >+        goto out;
> >+    }
> >+
> >+    if (!virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> >          vdev->vq[n].last_avail_idx = vring_used_idx(&vdev->vq[n]);
> >-        vdev->vq[n].shadow_avail_idx = vdev->vq[n].last_avail_idx;
> >      }
> >+    vdev->vq[n].shadow_avail_idx = vdev->vq[n].last_avail_idx;
> >+
> >+out:
> >      rcu_read_unlock();
> >  }
> >  void virtio_queue_update_used_idx(VirtIODevice *vdev, int n)
> >  {
> >      rcu_read_lock();
> >-    if (vdev->vq[n].vring.desc) {
> >+    if (!vdev->vq[n].vring.desc) {
> >+        goto out;
> >+    }
> >+
> >+    if (!virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> >          vdev->vq[n].used_idx = vring_used_idx(&vdev->vq[n]);
> >      }
> >+
> >+out:
> >      rcu_read_unlock();
> >  }
>