Subject: Re: [PATCH 1/2] vhost/vsock: fix incorrect used length reported to the guest

From: Halil Pasic <[email-masked]>
Date: Tue, 23 Nov 2021 14:22:29 +0100

On Mon, 22 Nov 2021 17:35:24 +0100
Stefano Garzarella <[email-masked]> wrote:

> The "used length" reported by calling vhost_add_used() must be the
> number of bytes written by the device (using "in" buffers).
> 
> In vhost_vsock_handle_tx_kick() the device only reads the guest
> buffers (they are all "out" buffers), without writing anything,
> so we must pass 0 as "used length" to comply virtio spec.
> 
> Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko")
> Cc: [email-masked]
> Reported-by: Halil Pasic <[email-masked]>
> Suggested-by: Jason Wang <[email-masked]>
> Signed-off-by: Stefano Garzarella <[email-masked]>

Reviewed-by: Halil Pasic <[email-masked]>

> ---
>  drivers/vhost/vsock.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index 938aefbc75ec..4e3b95af7ee4 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -554,7 +554,7 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
>  			virtio_transport_free_pkt(pkt);
>  
>  		len += sizeof(pkt->hdr);
> -		vhost_add_used(vq, head, len);
> +		vhost_add_used(vq, head, 0);
>  		total_len += len;
>  		added = true;
>  	} while(likely(!vhost_exceeds_weight(vq, ++pkts, total_len)));