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

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Message-ID: <20210601041351.GC203469@mtl-vdi-166.wap.labs.mlnx>
Date:   Tue, 1 Jun 2021 07:13:51 +0300
From:   Eli Cohen <elic@...dia.com>
To:     Jason Wang <jasowang@...hat.com>
CC:     <mst@...hat.com>, <virtualization@...ts.linux-foundation.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] vdpa/mlx5: Only return vq ready if vq is initialized

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@...dia.com>
> > ---
> >   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.

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."


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