netdev - Re: [PATCH net-next] veth: check for NAPI instead of xdp

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Date:   Fri, 16 Apr 2021 17:59:29 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     brouer@...hat.com, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH net-next] veth: check for NAPI instead of xdp_prog
 before xmit of XDP frame

On Fri, 16 Apr 2021 17:47:45 +0200
Toke Høiland-Jørgensen <toke@...hat.com> wrote:

> The recent patch that tied enabling of veth NAPI to the GRO flag also has
> the nice side effect that a veth device can be the target of an
> XDP_REDIRECT without an XDP program needing to be loaded on the peer
> device. However, the patch adding this extra NAPI mode didn't actually
> change the check in veth_xdp_xmit() to also look at the new NAPI pointer,
> so let's fix that.
> 
> Fixes: 6788fa154546 ("veth: allow enabling NAPI even without XDP")
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
>  drivers/net/veth.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)

Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>

Very happy to see this strange requirement of loading an xdp_prog on
the veth peer (inside the netns) being lifted.  Multiple people/users
have hit this issue and complained.  Thanks for the followup to fix
this! :-)

> diff --git a/drivers/net/veth.c b/drivers/net/veth.c
> index 15b2e3923c47..bdb7ce3cb054 100644
> --- a/drivers/net/veth.c
> +++ b/drivers/net/veth.c
> @@ -486,11 +486,10 @@ static int veth_xdp_xmit(struct net_device *dev, int n,
>  
>  	rcv_priv = netdev_priv(rcv);
>  	rq = &rcv_priv->rq[veth_select_rxq(rcv)];
> -	/* Non-NULL xdp_prog ensures that xdp_ring is initialized on receive
> -	 * side. This means an XDP program is loaded on the peer and the peer
> -	 * device is up.
> +	/* The napi pointer is set if NAPI is enabled, which ensures that
> +	 * xdp_ring is initialized on receive side and the peer device is up.
>  	 */
> -	if (!rcu_access_pointer(rq->xdp_prog))
> +	if (!rcu_access_pointer(rq->napi))
>  		goto out;
>  
>  	max_len = rcv->mtu + rcv->hard_header_len + VLAN_HLEN;



-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer