Re: [PATCH v1 1/2] virtio: struct VirtQueue introduce reset

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

On Sun, Jan 29, 2023 at 03:15:16PM +0800, Xuan Zhuo wrote:
> On Sun, 29 Jan 2023 02:12:36 -0500, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> >
> > subject seems wrong.
> 
> 
> Will fix.
> 
> 
> >
> > On Sun, Jan 29, 2023 at 10:51:49AM +0800, Xuan Zhuo wrote:
> > > In the current design, we stop the device from operating on the vring
> > > during per-queue reset by resetting the structure VirtQueue.
> > >
> > > But before the reset operation, when recycling some resources, we should
> > > stop referencing new vring resources. For example, when recycling
> > > virtio-net's asynchronous sending resources, virtio-net should be able
> > > to perceive that the current queue is in the per-queue reset state, and
> > > stop sending new packets from the tx queue.
> > >
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > ---
> > >  hw/virtio/virtio.c         | 15 +++++++++++++++
> > >  include/hw/virtio/virtio.h |  1 +
> > >  2 files changed, 16 insertions(+)
> > >
> > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > > index f35178f5fc..c954f2a2b3 100644
> > > --- a/hw/virtio/virtio.c
> > > +++ b/hw/virtio/virtio.c
> > > @@ -142,6 +142,8 @@ struct VirtQueue
> > >      /* Notification enabled? */
> > >      bool notification;
> > >
> > > +    bool disabled_by_reset;
> > > +
> > >      uint16_t queue_index;
> > >
> > >      unsigned int inuse;
> > > @@ -2079,6 +2081,12 @@ void virtio_queue_reset(VirtIODevice *vdev, uint32_t queue_index)
> > >  {
> > >      VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
> > >
> > > +    /*
> > > +     * Mark this queue is per-queue reset status. The device should release the
> > > +     * references of the vring, and not refer more new vring item.
> >
> > items
> 
> 
> Will fix.
> 
> >
> > > +     */
> > > +    vdev->vq[queue_index].disabled_by_reset = true;
> > > +
> > >      if (k->queue_reset) {
> > >          k->queue_reset(vdev, queue_index);
> > >      }
> >
> > can we set this after calling queue_reset? For symmetry with enable.
> 
> 
> In fact,  queue_reset() will check it.
> 

when you disable you first set it then disable.
so when we are not 100% ready it's already set.
when you enable you first clear it then enable.
so we are not 100% ready but it's no longer set.
inconsistent.


> >
> > > @@ -2102,11 +2110,18 @@ void virtio_queue_enable(VirtIODevice *vdev, uint32_t queue_index)
> > >      }
> > >      */
> > >
> > > +    vdev->vq[queue_index].disabled_by_reset = false;
> > > +
> > >      if (k->queue_enable) {
> > >          k->queue_enable(vdev, queue_index);
> > >      }
> > >  }
> > >
> > > +bool virtio_queue_reset_state(VirtQueue *vq)
> > > +{
> > > +    return vq->disabled_by_reset;
> > > +}
> > > +
> > >  void virtio_reset(void *opaque)
> > >  {
> > >      VirtIODevice *vdev = opaque;
> > > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > > index 77c6c55929..00e91af7c4 100644
> > > --- a/include/hw/virtio/virtio.h
> > > +++ b/include/hw/virtio/virtio.h
> > > @@ -319,6 +319,7 @@ int virtio_set_status(VirtIODevice *vdev, uint8_t val);
> > >  void virtio_reset(void *opaque);
> > >  void virtio_queue_reset(VirtIODevice *vdev, uint32_t queue_index);
> > >  void virtio_queue_enable(VirtIODevice *vdev, uint32_t queue_index);
> > > +bool virtio_queue_reset_state(VirtQueue *vq);
> > >  void virtio_update_irq(VirtIODevice *vdev);
> > >  int virtio_set_features(VirtIODevice *vdev, uint64_t val);
> >
> > OK I guess ... what about migration. This state won't be
> > set correctly will it?
> 
> I think it has no effect. After the reset, there is actually no state. We can
> migrate.
> 
> The current variable is only used by ->queue_reset().
> 
> Thanks.
> 

Yea maybe it works for this bug but ... yack. This means the state has
no logic consistency.  It's just there because you found a bug and
wanted to fix it.
An ultra specific
	bool this_weird_state_fuzzer_gets_in_issue_1451;
is hard to maintain, not happy :(


> >
> >
> > >
> > > --
> > > 2.32.0.3.g01195cf9f
> >