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

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

[Matt Fleming]

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

Re: [Intel-wired-lan] [PATCH net] ice: Fix missing 1's complement negation in GCS raw checksum

[Loktionov, Aleksandr]

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@osuosl.org> On Behalf
> Of Matt Fleming
> Sent: Wednesday, April 8, 2026 9:02 PM
> To: Nguyen, Anthony L <anthony.l.nguyen@intel.com>; Kitszel,
> Przemyslaw <przemyslaw.kitszel@intel.com>
> Cc: Andrew Lunn <andrew+netdev@lunn.ch>; David S . Miller
> <davem@davemloft.net>; Eric Dumazet <edumazet@google.com>; Jakub
> Kicinski <kuba@kernel.org>; Paolo Abeni <pabeni@redhat.com>; intel-
> wired-lan@lists.osuosl.org; netdev@vger.kernel.org; linux-
> kernel@vger.kernel.org; kernel-team@cloudflare.com; Matt Fleming
> <mfleming@cloudflare.com>
> Subject: [Intel-wired-lan] [PATCH net] ice: Fix missing 1's complement
> negation in GCS raw checksum
> 
> 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


I'd recommend adding Cc: stable@vger.kernel.org
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>