netdev - RE: [PATCH net-next v4 3/7] dpaa_eth: limit the possible MTU range when XDP is enabled

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Date:   Wed, 25 Nov 2020 15:47:44 +0000
From:   Camelia Alexandra Groza <camelia.groza@....com>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>
CC:     "kuba@...nel.org" <kuba@...nel.org>,
        "brouer@...hat.com" <brouer@...hat.com>,
        "saeed@...nel.org" <saeed@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "Madalin Bucur (OSS)" <madalin.bucur@....nxp.com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next v4 3/7] dpaa_eth: limit the possible MTU range
 when XDP is enabled

> -----Original Message-----
> From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> Sent: Tuesday, November 24, 2020 21:12
> To: Camelia Alexandra Groza <camelia.groza@....com>
> Cc: kuba@...nel.org; brouer@...hat.com; saeed@...nel.org;
> davem@...emloft.net; Madalin Bucur (OSS)
> <madalin.bucur@....nxp.com>; Ioana Ciornei <ioana.ciornei@....com>;
> netdev@...r.kernel.org
> Subject: Re: [PATCH net-next v4 3/7] dpaa_eth: limit the possible MTU range
> when XDP is enabled
> 
> On Mon, Nov 23, 2020 at 07:36:21PM +0200, Camelia Groza wrote:
> > Implement the ndo_change_mtu callback to prevent users from setting an
> > MTU that would permit processing of S/G frames. The maximum MTU size
> > is dependent on the buffer size.
> >
> > Acked-by: Madalin Bucur <madalin.bucur@....nxp.com>
> > Signed-off-by: Camelia Groza <camelia.groza@....com>
> > ---
> >  drivers/net/ethernet/freescale/dpaa/dpaa_eth.c | 40
> ++++++++++++++++++++------
> >  1 file changed, 31 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > index 8acce62..ee076f4 100644
> > --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > @@ -2756,23 +2756,44 @@ static int dpaa_eth_stop(struct net_device
> *net_dev)
> >  	return err;
> >  }
> >
> > +static bool xdp_validate_mtu(struct dpaa_priv *priv, int mtu)
> > +{
> > +	int max_contig_data = priv->dpaa_bp->size - priv->rx_headroom;
> > +
> > +	/* We do not support S/G fragments when XDP is enabled.
> > +	 * Limit the MTU in relation to the buffer size.
> > +	 */
> > +	if (mtu + VLAN_ETH_HLEN + ETH_FCS_LEN > max_contig_data) {
> 
> Do you support VLAN double tagging? We normally take into acount to two
> vlan
> headers in these checks.
> 
> Other than that:
> Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>

No, we only account for one.

> > +		dev_warn(priv->net_dev->dev.parent,
> > +			 "The maximum MTU for XDP is %d\n",
> > +			 max_contig_data - VLAN_ETH_HLEN -
> ETH_FCS_LEN);
> > +		return false;
> > +	}
> > +
> > +	return true;
> > +}
> > +
> > +static int dpaa_change_mtu(struct net_device *net_dev, int new_mtu)
> > +{
> > +	struct dpaa_priv *priv = netdev_priv(net_dev);
> > +
> > +	if (priv->xdp_prog && !xdp_validate_mtu(priv, new_mtu))
> > +		return -EINVAL;
> > +
> > +	net_dev->mtu = new_mtu;
> > +	return 0;
> > +}
> > +
> >  static int dpaa_setup_xdp(struct net_device *net_dev, struct bpf_prog
> *prog)
> >  {
> >  	struct dpaa_priv *priv = netdev_priv(net_dev);
> >  	struct bpf_prog *old_prog;
> > -	int err, max_contig_data;
> > +	int err;
> >  	bool up;
> >
> > -	max_contig_data = priv->dpaa_bp->size - priv->rx_headroom;
> > -
> >  	/* S/G fragments are not supported in XDP-mode */
> > -	if (prog &&
> > -	    (net_dev->mtu + VLAN_ETH_HLEN + ETH_FCS_LEN >
> max_contig_data)) {
> > -		dev_warn(net_dev->dev.parent,
> > -			 "The maximum MTU for XDP is %d\n",
> > -			 max_contig_data - VLAN_ETH_HLEN -
> ETH_FCS_LEN);
> > +	if (prog && !xdp_validate_mtu(priv, net_dev->mtu))
> >  		return -EINVAL;
> > -	}
> >
> >  	up = netif_running(net_dev);
> >
> > @@ -2870,6 +2891,7 @@ static int dpaa_ioctl(struct net_device *net_dev,
> struct ifreq *rq, int cmd)
> >  	.ndo_set_rx_mode = dpaa_set_rx_mode,
> >  	.ndo_do_ioctl = dpaa_ioctl,
> >  	.ndo_setup_tc = dpaa_setup_tc,
> > +	.ndo_change_mtu = dpaa_change_mtu,
> >  	.ndo_bpf = dpaa_xdp,
> >  };
> >
> > --
> > 1.9.1
> >