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Subject[PATCH 4.19 03/24] net/mlx5e: fix csum adjustments caused by RXFCS
Date
4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit d48051c5b8376038c2b287c3b1bd55b8d391d567 ]

As shown by Dmitris, we need to use csum_block_add() instead of csum_add()
when adding the FCS contribution to skb csum.

Before 4.18 (more exactly commit 88078d98d1bb "net: pskb_trim_rcsum()
and CHECKSUM_COMPLETE are friends"), the whole skb csum was thrown away,
so RXFCS changes were ignored.

Then before commit d55bef5059dd ("net: fix pskb_trim_rcsum_slow() with
odd trim offset") both mlx5 and pskb_trim_rcsum_slow() bugs were canceling
each other.

Now we fixed pskb_trim_rcsum_slow() we need to fix mlx5.

Note that this patch also rewrites mlx5e_get_fcs() to :

- Use skb_header_pointer() instead of reinventing it.
- Use __get_unaligned_cpu32() to avoid possible non aligned accesses
as Dmitris pointed out.

Fixes: 902a545904c7 ("net/mlx5e: When RXFCS is set, add FCS data into checksum calculation")
Reported-by: Paweł Staszewski <pstaszewski@itcare.pl>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Eran Ben Elisha <eranbe@mellanox.com>
Cc: Saeed Mahameed <saeedm@mellanox.com>
Cc: Dimitris Michailidis <dmichail@google.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Paweł Staszewski <pstaszewski@itcare.pl>
Reviewed-by: Eran Ben Elisha <eranbe@mellanox.com>
Tested-By: Maria Pasechnik <mariap@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 45 ++++--------------------
1 file changed, 9 insertions(+), 36 deletions(-)

--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -696,43 +696,15 @@ static inline bool is_last_ethertype_ip(
return (ethertype == htons(ETH_P_IP) || ethertype == htons(ETH_P_IPV6));
}

-static __be32 mlx5e_get_fcs(struct sk_buff *skb)
+static u32 mlx5e_get_fcs(const struct sk_buff *skb)
{
- int last_frag_sz, bytes_in_prev, nr_frags;
- u8 *fcs_p1, *fcs_p2;
- skb_frag_t *last_frag;
- __be32 fcs_bytes;
-
- if (!skb_is_nonlinear(skb))
- return *(__be32 *)(skb->data + skb->len - ETH_FCS_LEN);
-
- nr_frags = skb_shinfo(skb)->nr_frags;
- last_frag = &skb_shinfo(skb)->frags[nr_frags - 1];
- last_frag_sz = skb_frag_size(last_frag);
-
- /* If all FCS data is in last frag */
- if (last_frag_sz >= ETH_FCS_LEN)
- return *(__be32 *)(skb_frag_address(last_frag) +
- last_frag_sz - ETH_FCS_LEN);
-
- fcs_p2 = (u8 *)skb_frag_address(last_frag);
- bytes_in_prev = ETH_FCS_LEN - last_frag_sz;
-
- /* Find where the other part of the FCS is - Linear or another frag */
- if (nr_frags == 1) {
- fcs_p1 = skb_tail_pointer(skb);
- } else {
- skb_frag_t *prev_frag = &skb_shinfo(skb)->frags[nr_frags - 2];
+ const void *fcs_bytes;
+ u32 _fcs_bytes;

- fcs_p1 = skb_frag_address(prev_frag) +
- skb_frag_size(prev_frag);
- }
- fcs_p1 -= bytes_in_prev;
-
- memcpy(&fcs_bytes, fcs_p1, bytes_in_prev);
- memcpy(((u8 *)&fcs_bytes) + bytes_in_prev, fcs_p2, last_frag_sz);
+ fcs_bytes = skb_header_pointer(skb, skb->len - ETH_FCS_LEN,
+ ETH_FCS_LEN, &_fcs_bytes);

- return fcs_bytes;
+ return __get_unaligned_cpu32(fcs_bytes);
}

static inline void mlx5e_handle_csum(struct net_device *netdev,
@@ -765,8 +737,9 @@ static inline void mlx5e_handle_csum(str
network_depth - ETH_HLEN,
skb->csum);
if (unlikely(netdev->features & NETIF_F_RXFCS))
- skb->csum = csum_add(skb->csum,
- (__force __wsum)mlx5e_get_fcs(skb));
+ skb->csum = csum_block_add(skb->csum,
+ (__force __wsum)mlx5e_get_fcs(skb),
+ skb->len - ETH_FCS_LEN);
stats->csum_complete++;
return;
}

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