vdpa/mlx5: should exclude header length and fcs from mtu

When feature VIRTIO_NET_F_MTU is negotiated on mlx5_vdpa,
22 extra bytes worth of MTU length is shown in guest.
This is because the mlx5_query_port_max_mtu API returns
the "hardware" MTU value, which does not just contain the
 Ethernet payload, but includes extra lengths starting
from the Ethernet header up to the FCS altogether.

Fix the MTU so packets won't get dropped silently.

Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20210408091047.4269-2-elic@nvidia.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/vdpa/mlx5/core/mlx5_vdpa.h b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
index 08f742fd24099e4f5e616c4818336dfe9fd26ded..b6cc53ba980cccc1c90f0d952f7359bd59e7a137 100644 (file)
--- a/drivers/vdpa/mlx5/core/mlx5_vdpa.h
+++ b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
@@ -4,9 +4,13 @@
 #ifndef __MLX5_VDPA_H__
 #define __MLX5_VDPA_H__
 
+#include <linux/etherdevice.h>
+#include <linux/if_vlan.h>
 #include <linux/vdpa.h>
 #include <linux/mlx5/driver.h>
 
+#define MLX5V_ETH_HARD_MTU (ETH_HLEN + VLAN_HLEN + ETH_FCS_LEN)
+
 struct mlx5_vdpa_direct_mr {
        u64 start;
        u64 end;

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index 71397fdafa6a4c013f680afefb51acf74108ad57..a49ebb250253ac6e93acda7a9902ebe21e6303f5 100644 (file)
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -1907,6 +1907,19 @@ static const struct vdpa_config_ops mlx5_vdpa_ops = {
        .free = mlx5_vdpa_free,
 };
 
+static int query_mtu(struct mlx5_core_dev *mdev, u16 *mtu)
+{
+       u16 hw_mtu;
+       int err;
+
+       err = mlx5_query_nic_vport_mtu(mdev, &hw_mtu);
+       if (err)
+               return err;
+
+       *mtu = hw_mtu - MLX5V_ETH_HARD_MTU;
+       return 0;
+}
+
 static int alloc_resources(struct mlx5_vdpa_net *ndev)
 {
        struct mlx5_vdpa_net_resources *res = &ndev->res;
@@ -1992,7 +2005,7 @@ static int mlx5v_probe(struct auxiliary_device *adev,
        init_mvqs(ndev);
        mutex_init(&ndev->reslock);
        config = &ndev->config;
-       err = mlx5_query_nic_vport_mtu(mdev, &ndev->mtu);
+       err = query_mtu(mdev, &ndev->mtu);
        if (err)
                goto err_mtu;