Re: [PATCH 2/3] virtio: struct VirtQueue introduce reset

[Xuan Zhuo]

On Sat, 28 Jan 2023 05:22:05 -0500, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> On Sat, Jan 28, 2023 at 03:17:23PM +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         | 8 ++++++++
> >  include/hw/virtio/virtio.h | 3 +++
> >  2 files changed, 11 insertions(+)
> >
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index 03077b2ecf..907d5b8bde 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -2030,6 +2030,12 @@ 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.
> > +     */
> > +    vdev->vq[queue_index].reset = true;
> > +
> >      if (k->queue_reset) {
> >          k->queue_reset(vdev, queue_index);
> >      }
> > @@ -2053,6 +2059,8 @@ void virtio_queue_enable(VirtIODevice *vdev, uint32_t 
> > queue_index)
> >      }
> >      */
> >
> > +    vdev->vq[queue_index].reset = false;
> > +
> >      if (k->queue_enable) {
> >          k->queue_enable(vdev, queue_index);
> >      }
> > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > index 1c0d77c670..b888538d09 100644
> > --- a/include/hw/virtio/virtio.h
> > +++ b/include/hw/virtio/virtio.h
> > @@ -251,6 +251,9 @@ struct VirtQueue {
> >      /* Notification enabled? */
> >      bool notification;
> >
> > +    /* Per-Queue Reset status */
> > +    bool reset;
> > +
> >      uint16_t queue_index;
> >
>
> Reset state makes no sense. It seems to imply queue_reset
> in the spec. And for extra fun there's "reset" in the pci
> proxy which means "virtio_queue_reset is in progress" - I have no
> idea what uses it though - it is not guest visible.  First what is it?
> It actually means "queue has been reset and not has not been enabled since".
> So disabled_by_reset maybe?


In fact, when reading this, the queue has not been reset,
so prepare_for_reset?

>
> Second this hack helps make the change minimal
> so it's helpful for stable, but it's ugly in that it
> duplicates the reverse of enabled value - we don't really
> care what disabled it in practice.
>
> With the fixups above I can apply so it's easier to backport, but later
> a patch on top should clean it all up, perhaps by adding
> "enabled" in VirtQueue. We should also get rid of "reset" in the proxy
> unless there's some way it's useful which I don't currently see.
>

I have some confusion, I don't understand what you mean.

Why did we remove the "reset" in the proxy?

I agree to rename the "reset".

Thanks.

>
>
> >      unsigned int inuse;
> > --
> > 2.32.0.3.g01195cf9f
>