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

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Date:   Tue, 23 Nov 2021 14:22:29 +0100
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>, netdev@...r.kernel.org,
        kvm@...r.kernel.org, Asias He <asias@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH 1/2] vhost/vsock: fix incorrect used length reported to
 the guest

On Mon, 22 Nov 2021 17:35:24 +0100
Stefano Garzarella <sgarzare@...hat.com> 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: stable@...r.kernel.org
> Reported-by: Halil Pasic <pasic@...ux.ibm.com>
> Suggested-by: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>

Reviewed-by: Halil Pasic <pasic@...ux.ibm.com>

> ---
>  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)));