Re: [PATCH V2] virtio-pci: fix queue_enable write

[Jason Wang]

On 2020/6/10 下午5:52, Stefano Garzarella wrote:
> On Wed, Jun 10, 2020 at 05:42:54AM -0400, Michael S. Tsirkin wrote:
> > On Wed, Jun 10, 2020 at 10:57:26AM +0200, Stefano Garzarella wrote:
> > > On Wed, Jun 10, 2020 at 01:43:51PM +0800, Jason Wang wrote:
> > > > Spec said: The driver uses this to selectively prevent the device from
> > > > executing requests from this virtqueue. 1 - enabled; 0 - disabled.
> > > >
> > > > Though write 0 to queue_enable is forbidden by the spec, we should not
> > > > assume that the value is 1.
> > > >
> > > > Fix this by ignore the write value other than 1.
> > > >
> > > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > > ---
> > > > Changes from V1:
> > > > - fix typo
> > > > - warn wrong value through virtio_error
> > > > ---
> > > >   hw/virtio/virtio-pci.c | 12 ++++++++----
> > > >   1 file changed, 8 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > > > index d028c17c24..7bc8c1c056 100644
> > > > --- a/hw/virtio/virtio-pci.c
> > > > +++ b/hw/virtio/virtio-pci.c
> > > > @@ -1273,16 +1273,20 @@ static void virtio_pci_common_write(void *opaque, 
> > > > hwaddr addr,
> > > >           virtio_queue_set_vector(vdev, vdev->queue_sel, val);
> > > >           break;
> > > >       case VIRTIO_PCI_COMMON_Q_ENABLE:
> > > > -        virtio_queue_set_num(vdev, vdev->queue_sel,
> > > > -                             proxy->vqs[vdev->queue_sel].num);
> > > > -        virtio_queue_set_rings(vdev, vdev->queue_sel,
> > > > +        if (val == 1) {
> > > Does it have to be 1 or can it be any value other than 0?
> > >
> > > Thanks,
> > > Stefano
> > spec says 1
> I was confused by "The driver MUST NOT write a 0 to queue_enable.",
> interpreting it as "can write anything other than 0".


Yes, the spec is unclear about what happens if we write a value other 
than 0 or 1.

Maybe we should clarify that only 1 is allowed. Or writing value other 
than 1 may cause unexpected result.


> But as Jason also wrote in the commit message, the driver should write
> 1 to enable, so
>
> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>


Thanks


> Thanks,
> Stefano