Subject: Re: [PATCH net-next 2/4] virtio_net: Remove command data from control_buf

From: Simon Horman <[email-masked]>
Date: Thu, 28 Mar 2024 13:35:16 +0000

On Mon, Mar 25, 2024 at 04:49:09PM -0500, Daniel Jurgens wrote:
> Allocate memory for the data when it's used. Ideally the could be on the
> stack, but we can't DMA stack memory. With this change only the header
> and status memory are shared between commands, which will allow using a
> tighter lock than RTNL.
> 
> Signed-off-by: Daniel Jurgens <[email-masked]>
> Reviewed-by: Jiri Pirko <[email-masked]>

...

> @@ -3893,10 +3925,16 @@ static int virtnet_restore_up(struct virtio_device *vdev)
>  
>  static int virtnet_set_guest_offloads(struct virtnet_info *vi, u64 offloads)
>  {
> +	u64 *_offloads __free(kfree) = NULL;
>  	struct scatterlist sg;
> -	vi->ctrl->offloads = cpu_to_virtio64(vi->vdev, offloads);
>  
> -	sg_init_one(&sg, &vi->ctrl->offloads, sizeof(vi->ctrl->offloads));
> +	_offloads = kzalloc(sizeof(*_offloads), GFP_KERNEL);
> +	if (!_offloads)
> +		return -ENOMEM;
> +
> +	*_offloads = cpu_to_virtio64(vi->vdev, offloads);

Hi Daniel,

There is a type mismatch between *_offloads and cpu_to_virtio64
which is flagged by Sparse as follows:

 .../virtio_net.c:3978:20: warning: incorrect type in assignment (different base types)
 .../virtio_net.c:3978:20:    expected unsigned long long [usertype]
 .../virtio_net.c:3978:20:    got restricted __virtio64

I think this can be addressed by changing the type of *_offloads to
__virtio64 *.

> +
> +	sg_init_one(&sg, _offloads, sizeof(*_offloads));
>  
>  	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_GUEST_OFFLOADS,
>  				  VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET, &sg)) {
> -- 
> 2.42.0
> 
>