[PATCH net-next v2 3/7] dpaa_eth: limit the possible MTU range when XDP is enabled

[Camelia Groza <camelia.groza@nxp.com>]

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.

Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
---
 drivers/net/ethernet/freescale/dpaa/dpaa_eth.c | 32 ++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
index 6b9ca60..5da4f17 100644
--- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
+++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
@@ -2746,6 +2746,34 @@ 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) {
+		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);
@@ -2754,8 +2782,7 @@ static int dpaa_setup_xdp(struct net_device *net_dev, struct bpf_prog *prog)
 	int err;
 
 	/* S/G fragments are not supported in XDP-mode */
-	if (prog && (priv->dpaa_bp->raw_size <
-	    net_dev->mtu + VLAN_ETH_HLEN + ETH_FCS_LEN))
+	if (prog && !xdp_validate_mtu(priv, net_dev->mtu))
 		return -EINVAL;
 
 	up = netif_running(net_dev);
@@ -2852,6 +2879,7 @@ 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