[PATCH linux-next v2 12/14] vdpa/mlx5: should exclude header length and fcs from mtu

[Parav Pandit <parav@nvidia.com>]

From: Si-Wei Liu <si-wei.liu@oracle.com>

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>
---
 drivers/vdpa/mlx5/core/mlx5_vdpa.h |  4 +++
 drivers/vdpa/mlx5/net/mlx5_vnet.c  | 42 +++++++++++++++++++++---------
 2 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/drivers/vdpa/mlx5/core/mlx5_vdpa.h b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
index 08f742fd2409..b6cc53ba980c 100644
--- 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 c342cc9355e8..56d463d2be85 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -1526,17 +1526,8 @@ static u64 mlx_to_vritio_features(u16 dev_features)
 static u64 mlx5_vdpa_get_features(struct vdpa_device *vdev)
 {
 	struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
-	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
-	u16 dev_features;
 
-	dev_features = MLX5_CAP_DEV_VDPA_EMULATION(mvdev->mdev, device_features_bits_mask);
-	ndev->mvdev.mlx_features = mlx_to_vritio_features(dev_features);
-	if (MLX5_CAP_DEV_VDPA_EMULATION(mvdev->mdev, virtio_version_1_0))
-		ndev->mvdev.mlx_features |= BIT_ULL(VIRTIO_F_VERSION_1);
-	ndev->mvdev.mlx_features |= BIT_ULL(VIRTIO_F_ACCESS_PLATFORM) |
-				     BIT_ULL(VIRTIO_NET_F_MAC);
-	print_features(mvdev, ndev->mvdev.mlx_features, false);
-	return ndev->mvdev.mlx_features;
+	return mvdev->mlx_features;
 }
 
 static int verify_min_features(struct mlx5_vdpa_dev *mvdev, u64 features)
@@ -1834,7 +1825,6 @@ static void mlx5_vdpa_set_status(struct vdpa_device *vdev, u8 status)
 		clear_virtqueues(ndev);
 		mlx5_vdpa_destroy_mr(&ndev->mvdev);
 		ndev->mvdev.status = 0;
-		ndev->mvdev.mlx_features = 0;
 		++mvdev->generation;
 		return;
 	}
@@ -1990,6 +1980,33 @@ static const struct vdpa_config_ops mlx5_vdpa_ops = {
 	.free = mlx5_vdpa_free,
 };
 
+static void query_virtio_features(struct mlx5_vdpa_net *ndev)
+{
+	struct mlx5_vdpa_dev *mvdev = &ndev->mvdev;
+	u16 dev_features;
+
+	dev_features = MLX5_CAP_DEV_VDPA_EMULATION(mvdev->mdev, device_features_bits_mask);
+	mvdev->mlx_features = mlx_to_vritio_features(dev_features);
+	if (MLX5_CAP_DEV_VDPA_EMULATION(mvdev->mdev, virtio_version_1_0))
+		mvdev->mlx_features |= BIT_ULL(VIRTIO_F_VERSION_1) |
+				       BIT_ULL(VIRTIO_NET_F_MAC);
+	mvdev->mlx_features |= BIT_ULL(VIRTIO_F_ACCESS_PLATFORM);
+	print_features(mvdev, mvdev->mlx_features, false);
+}
+
+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;
@@ -2084,7 +2101,8 @@ static int mlx5_vdpa_dev_add(struct vdpa_mgmt_dev *v_mdev, const char *name)
 	init_mvqs(ndev);
 	mutex_init(&ndev->reslock);
 	config = &ndev->config;
-	err = mlx5_query_nic_vport_mtu(mdev, &ndev->mtu);
+	query_virtio_features(ndev);
+	err = query_mtu(mdev, &ndev->mtu);
 	if (err)
 		goto err_mtu;
 
-- 
2.26.2

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