net/mlx5: Avoid panic when setting vport rate

If we try to set VFs rate on a VF (not PF) net device, the kernel
will be crash. The commands are show as below:

$ echo 2 > /sys/class/net/$MLX_PF0/device/sriov_numvfs
$ ip link set $MLX_VF0 vf 0 max_tx_rate 2 min_tx_rate 1

If not applied the first patch ("net/mlx5: Avoid panic when setting
vport mac, getting vport config"), the command:

$ ip link set $MLX_VF0 vf 0 rate 100

can also crash the kernel.

[ 1650.006388] RIP: 0010:mlx5_eswitch_set_vport_rate+0x1f/0x260 [mlx5_core]
[ 1650.007092]  do_setlink+0x982/0xd20
[ 1650.007129]  __rtnl_newlink+0x528/0x7d0
[ 1650.007374]  rtnl_newlink+0x43/0x60
[ 1650.007407]  rtnetlink_rcv_msg+0x2a2/0x320
[ 1650.007484]  netlink_rcv_skb+0xcb/0x100
[ 1650.007519]  netlink_unicast+0x17f/0x230
[ 1650.007554]  netlink_sendmsg+0x2d2/0x3d0
[ 1650.007592]  sock_sendmsg+0x36/0x50
[ 1650.007625]  ___sys_sendmsg+0x280/0x2a0
[ 1650.007963]  __sys_sendmsg+0x58/0xa0
[ 1650.007998]  do_syscall_64+0x5b/0x180
[ 1650.009438]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: c9497c98 ("net/mlx5: Add support for setting VF min rate")
Cc: Mohamad Haj Yahia <mohamad@mellanox.com>
Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/ethernet/mellanox/mlx5/core/eswitch.c

@@ -2297,19 +2297,24 @@ static int normalize_vports_min_rate(struct mlx5_eswitch *esw, u32 divider)
 int mlx5_eswitch_set_vport_rate(struct mlx5_eswitch *esw, int vport,
 				u32 max_rate, u32 min_rate)
 {
-	u32 fw_max_bw_share = MLX5_CAP_QOS(esw->dev, max_tsar_bw_share);
-	bool min_rate_supported = MLX5_CAP_QOS(esw->dev, esw_bw_share) &&
-					fw_max_bw_share >= MLX5_MIN_BW_SHARE;
-	bool max_rate_supported = MLX5_CAP_QOS(esw->dev, esw_rate_limit);
 	struct mlx5_vport *evport;
+	u32 fw_max_bw_share;
 	u32 previous_min_rate;
 	u32 divider;
+	bool min_rate_supported;
+	bool max_rate_supported;
 	int err = 0;
 
 	if (!ESW_ALLOWED(esw))
 		return -EPERM;
 	if (!LEGAL_VPORT(esw, vport))
 		return -EINVAL;
+
+	fw_max_bw_share = MLX5_CAP_QOS(esw->dev, max_tsar_bw_share);
+	min_rate_supported = MLX5_CAP_QOS(esw->dev, esw_bw_share) &&
+				fw_max_bw_share >= MLX5_MIN_BW_SHARE;
+	max_rate_supported = MLX5_CAP_QOS(esw->dev, esw_rate_limit);
+
 	if ((min_rate && !min_rate_supported) || (max_rate && !max_rate_supported))
 		return -EOPNOTSUPP;