Re: [PATCH 2/3] vdpa/mlx5: Only return vq ready if vq is initialized

[Jason Wang]

在 2021/6/1 下午12:13, Eli Cohen 写道:
> On Tue, Jun 01, 2021 at 10:18:04AM +0800, Jason Wang wrote:
> > 在 2021/6/1 上午12:04, Eli Cohen 写道:
> > > Only return the value of the ready field if the VQ is initialized in
> > > which case the value of the field is valid.
> > >
> > > Failing to do so can result in virtio_vdpa failing to load if the device
> > > was previously used by vhost_vdpa and the old values are ready.
> > > virtio_vdpa expects to find VQs in "not ready" state.
> > >
> > > Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
> > > Signed-off-by: Eli Cohen <elic@xxxxxxxxxx>
> > > ---
> > >    drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 +-
> > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > index 02a05492204c..f6b680d2ab1c 100644
> > > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > @@ -1407,7 +1407,7 @@ static bool mlx5_vdpa_get_vq_ready(struct vdpa_device *vdev, u16 idx)
> > >    	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
> > >    	struct mlx5_vdpa_virtqueue *mvq = &ndev->vqs[idx];
> > > -	return mvq->ready;
> > > +	return mvq->initialized && mvq->ready;
> >
> > I think the more suitable fix is to reset mvq->ready during reset. The
> > vq_ready should follow the queue_enable semantic in virtio-pci:
> >
> > "
> > The device MUST present a 0 in queue_enable on reset.
> > "
> Thinking again, I think we should call set_vq_ready() from
> qemu/virtio_vdpa etc. after reset to explicitly set ready to false.


This is not what I read from the spec and how the current driver behave.

And I don't see why we need to stick to 1 after the reset.


> The ready indication is not necessairily a reflection of the hardware
> queue:
>
> "Virtual queue ready bit
> Writing one (0x1) to this register notifies the device that it can
> execute requests from this virtual queue. Reading from this register
> returns the last value written to it. Both read and write accesses apply
> to the queue selected by writing to QueueSel."


My understanding that this applies if not reset in the middle. We can 
clarify this in the spec if needed.

Thanks


> > Thanks
> >
> >
> > >    }
> > >    static int mlx5_vdpa_set_vq_state(struct vdpa_device *vdev, u16 idx,