netdev - Re: [PATCH] vdpa/mlx5: Setup driver only if VIRTIO_CONFIG_S_DRIVER

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Message-ID: <20200907110335.GA121033@mtl-vdi-166.wap.labs.mlnx>
Date:   Mon, 7 Sep 2020 14:03:35 +0300
From:   Eli Cohen <elic@...dia.com>
To:     Jason Wang <jasowang@...hat.com>
CC:     "Michael S. Tsirkin" <mst@...hat.com>, Cindy Lu <lulu@...hat.com>,
        <virtualization@...ts.linux-foundation.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] vdpa/mlx5: Setup driver only if VIRTIO_CONFIG_S_DRIVER_OK

On Mon, Sep 07, 2020 at 06:53:23AM -0400, Jason Wang wrote:
> 
> 
> ----- Original Message -----
> > If the memory map changes before the driver status is
> > VIRTIO_CONFIG_S_DRIVER_OK, don't attempt to create resources because it
> > may fail. For example, if the VQ is not ready there is no point in
> > creating resources.
> > 
> > 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 | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > index 9df69d5efe8c..c89cd48a0aab 100644
> > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > @@ -1645,6 +1645,9 @@ static int mlx5_vdpa_change_map(struct mlx5_vdpa_net
> > *ndev, struct vhost_iotlb *
> >  	if (err)
> >  		goto err_mr;
> >  
> > +	if (!(ndev->mvdev.status & VIRTIO_CONFIG_S_DRIVER_OK))
> > +		return 0;
> > +
> 
> I'm not sure I get this.
> 
> It looks to me if set_map() is called before DRIVER_OK, we won't build
> any mapping?
> 
What would prevent that? Is it some qemu logic you're relying upon?
With current qemu 5.1 with lack of batching support, I get plenty calls
to set_map which result in calls to mlx5_vdpa_change_map().
If that happens before VIRTIO_CONFIG_S_DRIVER_OK then Imay fail (in case
I was not called to set VQs ready).

> 
> >  	restore_channels_info(ndev);
> >  	err = setup_driver(ndev);
> >  	if (err)
> > --
> > 2.26.0
> > 
> > 
>