Re: [PULL v2 31/41] virtio-pci: implement queue_enabled method

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

On Mon, Jul 27, 2020 at 03:51:41PM +0200, Laurent Vivier wrote:
> On 04/07/2020 20:30, Michael S. Tsirkin wrote:
> > From: Jason Wang <jasowang@redhat.com>
> > 
> > With version 1, we can detect whether a queue is enabled via
> > queue_enabled.
> > 
> > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > Signed-off-by: Cindy Lu <lulu@redhat.com>
> > Message-Id: <20200701145538.22333-5-lulu@redhat.com>
> > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > Acked-by: Jason Wang <jasowang@redhat.com>
> > ---
> >  hw/virtio/virtio-pci.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > index 7bc8c1c056..8554cf2a03 100644
> > --- a/hw/virtio/virtio-pci.c
> > +++ b/hw/virtio/virtio-pci.c
> > @@ -1107,6 +1107,18 @@ static AddressSpace *virtio_pci_get_dma_as(DeviceState *d)
> >      return pci_get_address_space(dev);
> >  }
> >  
> > +static bool virtio_pci_queue_enabled(DeviceState *d, int n)
> > +{
> > +    VirtIOPCIProxy *proxy = VIRTIO_PCI(d);
> > +    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
> > +
> > +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) {
> > +        return proxy->vqs[vdev->queue_sel].enabled;
> > +    }
> > +
> > +    return virtio_queue_enabled(vdev, n);
> > +}
> 
> With "disable-legacy=off,disable-modern=true",
> this changes introduces an infinite loop: virtio_queue_enabled() calls
> again virtio_pci_queue_enabled() that calls
> againvirtio_pci_queue_enabled()...
> 
> I think this should be changed like this:
> 
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index ada1101d07..0a85c17e91 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -1116,7 +1116,7 @@ static bool virtio_pci_queue_enabled(DeviceState
> *d, int n)
>          return proxy->vqs[vdev->queue_sel].enabled;
>      }
> 
> -    return virtio_queue_enabled(vdev, n);
> +    return virtio_queue_get_desc_addr(vdev, n) != 0;
>  }
> 

Thanks for the report and debugging the issue!

Maybe move
       return virtio_queue_get_desc_addr(vdev, n) != 0;
to a new API
	virtio_pci_queue_enabled_legacy()

to avoid code duplication.

Could you cook up a patch pls? don't forget the Fixes: tag
so people remember to backport it.




> > +
> >  static int virtio_pci_add_mem_cap(VirtIOPCIProxy *proxy,
> >                                     struct virtio_pci_cap *cap)
> >  {
> > @@ -2064,6 +2076,7 @@ static void virtio_pci_bus_class_init(ObjectClass *klass, void *data)
> >      k->ioeventfd_enabled = virtio_pci_ioeventfd_enabled;
> >      k->ioeventfd_assign = virtio_pci_ioeventfd_assign;
> >      k->get_dma_as = virtio_pci_get_dma_as;
> > +    k->queue_enabled = virtio_pci_queue_enabled;
> >  }
> >  
> >  static const TypeInfo virtio_pci_bus_info = {
> > 
> 
> Thanks,
> Laurent