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net/mlx5e: Fix the max MTU check in case of XDP 

MLX5E_XDP_MAX_MTU was calculated incorrectly. It didn't account for
NET_IP_ALIGN and MLX5E_HW2SW_MTU, and it also misused MLX5_SKB_FRAG_SZ.
This commit fixes the calculations and adds a brief explanation for the
formula used.

Fixes: a26a5bdf3e ("net/mlx5e: Restrict the combination of large MTU and XDP")
Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
This commit is contained in:
Maxim Mikityanskiy 2019-04-08 15:12:45 +03:00 committed by Saeed Mahameed
parent 12fc512f57
commit d460c27189
3 changed files with 24 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
View File

@ -33,6 +33,26 @@
#include <linux/bpf_trace.h>
#include "en/xdp.h"
int mlx5e_xdp_max_mtu(struct mlx5e_params *params)
{
int hr = NET_IP_ALIGN + XDP_PACKET_HEADROOM;
/* Let S := SKB_DATA_ALIGN(sizeof(struct skb_shared_info)).
* The condition checked in mlx5e_rx_is_linear_skb is:
* SKB_DATA_ALIGN(sw_mtu + hard_mtu + hr) + S <= PAGE_SIZE (1)
* (Note that hw_mtu == sw_mtu + hard_mtu.)
* What is returned from this function is:
* max_mtu = PAGE_SIZE - S - hr - hard_mtu (2)
* After assigning sw_mtu := max_mtu, the left side of (1) turns to
* SKB_DATA_ALIGN(PAGE_SIZE - S) + S, which is equal to PAGE_SIZE,
* because both PAGE_SIZE and S are already aligned. Any number greater
* than max_mtu would make the left side of (1) greater than PAGE_SIZE,
* so max_mtu is the maximum MTU allowed.
*/
return MLX5E_HW2SW_MTU(params, SKB_MAX_HEAD(hr));
}
static inline bool
mlx5e_xmit_xdp_buff(struct mlx5e_xdpsq *sq, struct mlx5e_dma_info *di,
struct xdp_buff *xdp)

3
drivers/net/ethernet/mellanox/mlx5/core/en/xdp.h
View File

@ -34,13 +34,12 @@
#include "en.h"
#define MLX5E_XDP_MAX_MTU ((int)(PAGE_SIZE - \
MLX5_SKB_FRAG_SZ(XDP_PACKET_HEADROOM)))
#define MLX5E_XDP_MIN_INLINE (ETH_HLEN + VLAN_HLEN)
#define MLX5E_XDP_TX_EMPTY_DS_COUNT \
(sizeof(struct mlx5e_tx_wqe) / MLX5_SEND_WQE_DS)
#define MLX5E_XDP_TX_DS_COUNT (MLX5E_XDP_TX_EMPTY_DS_COUNT + 1 /* SG DS */)
int mlx5e_xdp_max_mtu(struct mlx5e_params *params);
bool mlx5e_xdp_handle(struct mlx5e_rq *rq, struct mlx5e_dma_info *di,
void *va, u16 *rx_headroom, u32 *len);
bool mlx5e_poll_xdpsq_cq(struct mlx5e_cq *cq, struct mlx5e_rq *rq);

5
drivers/net/ethernet/mellanox/mlx5/core/en_main.c
View File

@ -3777,7 +3777,7 @@ int mlx5e_change_mtu(struct net_device *netdev, int new_mtu,
if (params->xdp_prog &&
!mlx5e_rx_is_linear_skb(priv->mdev, &new_channels.params)) {
netdev_err(netdev, "MTU(%d) > %d is not allowed while XDP enabled\n",
new_mtu, MLX5E_XDP_MAX_MTU);
new_mtu, mlx5e_xdp_max_mtu(params));
err = -EINVAL;
goto out;
}
@ -4212,7 +4212,8 @@ static int mlx5e_xdp_allowed(struct mlx5e_priv *priv, struct bpf_prog *prog)
if (!mlx5e_rx_is_linear_skb(priv->mdev, &new_channels.params)) {
netdev_warn(netdev, "XDP is not allowed with MTU(%d) > %d\n",
new_channels.params.sw_mtu, MLX5E_XDP_MAX_MTU);
new_channels.params.sw_mtu,
mlx5e_xdp_max_mtu(&new_channels.params));
return -EINVAL;
}