Patch "vdpa/mlx5: should exclude header length and fcs from mtu" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     vdpa-mlx5-should-exclude-header-length-and-fcs-from-.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit a86a71d901bb025ce0f9b0d02e2518ab57029d29
Author: Si-Wei Liu <si-wei.liu@xxxxxxxxxx>
Date:   Thu Apr 8 12:10:43 2021 +0300

    vdpa/mlx5: should exclude header length and fcs from mtu
    
    [ Upstream commit d084d996aaf53c0cc583dc75a4fc2a67fe485846 ]
    
    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@xxxxxxxxxx>
    Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
    Acked-by: Eli Cohen <elic@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20210408091047.4269-2-elic@xxxxxxxxxx
    Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

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 36e5933f11bc..545160ee2a62 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -1887,6 +1887,19 @@ 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;
@@ -1969,7 +1982,7 @@ void *mlx5_vdpa_add_dev(struct mlx5_core_dev *mdev)
 	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;