netdev - Re: [PATCH v2] vdpa/mlx5: Setup driver only if VIRTIO_CONFIG_S_DRIVER

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Date:   Wed, 9 Sep 2020 08:30:45 +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 v2] vdpa/mlx5: Setup driver only if
 VIRTIO_CONFIG_S_DRIVER_OK

On Tue, Sep 08, 2020 at 10:08:39PM -0400, Jason Wang wrote:
> 
> 
> ----- Original Message -----
> > set_map() is used by mlx5 vdpa to create a memory region based on the
> > address map passed by the iotlb argument. If we get successive calls, we
> > will destroy the current memory region and build another one based on
> > the new address mapping. We also need to setup the hardware resources
> > since they depend on the memory region.
> > 
> > If these calls happen before DRIVER_OK, It means that driver VQs may
> > also not been setup and we may not create them yet. In this case we want
> > to avoid setting up the other resources and defer this till we get
> > DRIVER OK.
> > 
> > Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
> > Signed-off-by: Eli Cohen <elic@...dia.com>
> > ---
> > V1->V2: Improve changelog description
> > 
> >  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;
> > +
> 
> Is there any reason that we still need to do vq suspending and saving before?
> 
Though suspend_vqs() and save_channels_info() will be called, they will
not actually do any work because the mvq->initialized is false.

Since we don't expect so many false map updates I think it makes sense
to avoid logic around the calls suspend_vqs() and save_channels_info().

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