> A veth device advertises NETDEV_XDP_ACT_NDO_XMIT only if its peer has an
> XDP program attached or GRO enabled, that is, only if the peer will have
> NAPI to receive the frames.
> 
> veth_set_features() updates the peer's flag when GRO is toggled, but
> returns early if the device is down, and veth_open() only refreshes the
> flags of the device being opened. Toggling GRO while the device is down
> therefore leaves the peer's flag stale after the device comes up.
> 
> If GRO was enabled while down, the device comes up with NAPI but the
> peer does not advertise NDO_XMIT, and devmap rejects redirects to the
> peer with -EOPNOTSUPP. If GRO was disabled while down, the device comes
> up without NAPI but the peer still advertises NDO_XMIT, so redirects are
> accepted and then dropped in veth_xdp_xmit() with -ENXIO.
> 
> Commit 7a6102aa6df0 ("veth: Update XDP feature set when bringing up
> device") made veth_open() refresh the device's own flags. Refresh the
> peer's flags there too. The peer's flag depends on this device's XDP
> program and GRO setting, not on whether the peer is up, so it is
> correct to set it even if the peer is down.
> 
> Fixes: 8267fc71abb2 ("veth: take into account peer device for NETDEV_XDP_ACT_NDO_XMIT xdp_features flag")
> Signed-off-by: Tianyi Gao <tianyi@cloudflare.com>

Acked-by: Lorenzo Bianconi <lorenzo.bianconi@oss.qualcomm.com>

> ---
>  drivers/net/veth.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/veth.c b/drivers/net/veth.c
> index 71227d0389aa..643b97dc5245 100644
> --- a/drivers/net/veth.c
> +++ b/drivers/net/veth.c
> @@ -1415,6 +1415,7 @@ static int veth_open(struct net_device *dev)
>  	}
>  
>  	veth_set_xdp_features(dev);
> +	veth_set_xdp_features(peer);
>  
>  	return 0;
>  }
> -- 
> 2.55.0
>