[PATCH net] ice: Fix missing 1's complement negation in GCS raw checksum

[Matt Fleming <matt@readmodwrite.com>]

From: Matt Fleming <mfleming@cloudflare.com>

Commit 905d1a220e8d ("ice: Add E830 checksum offload support") added
Generic Checksum (GCS) support for E830 NICs but omitted the 1's
complement negation (~) when converting the hardware raw_csum to
skb->csum for CHECKSUM_COMPLETE.

Without the negation, every CHECKSUM_COMPLETE packet fails the
fast-path validation in nf_ip_checksum() and falls through to software
checksumming via __skb_checksum_complete(), which triggers the
rate-limited "hw csum failure" warning. Packets are still accepted
(the software recheck passes) but hardware checksum offload is
effectively disabled and the warning floods dmesg on systems running
nf_conntrack on VLAN sub-interfaces.

Multiple other drivers (idpf, ehea, iwlwifi, cassini, sunhme, enetc)
also apply ~ for CHECKSUM_COMPLETE. The ice driver was the only in-tree
user of csum_unfold() for CHECKSUM_COMPLETE that omitted it.

Fixes: 905d1a220e8d ("ice: Add E830 checksum offload support")
Signed-off-by: Matt Fleming <mfleming@cloudflare.com>
---
 drivers/net/ethernet/intel/ice/ice_txrx_lib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/ice/ice_txrx_lib.c b/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
index e695a664e53d..c177579e0114 100644
--- a/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
+++ b/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
@@ -92,7 +92,7 @@ static void ice_rx_gcs(struct sk_buff *skb,
 	desc = (struct ice_32b_rx_flex_desc_nic *)rx_desc;
 	skb->ip_summed = CHECKSUM_COMPLETE;
 	csum = (__force u16)desc->raw_csum;
-	skb->csum = csum_unfold((__force __sum16)swab16(csum));
+	skb->csum = csum_unfold((__force __sum16)~swab16(csum));
 }
 
 /**
-- 
2.43.0