netdev - Re: [RFC PATCH net-next] net: Modify CSUM capability check for USO

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Message-ID: <0b1cdac7-662a-4e27-b8b0-836cdba1d460@redhat.com>
Date: Wed, 12 Mar 2025 17:14:21 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Radharapu Rakesh <rakesh.radharapu@....com>, git@....com,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, horms@...nel.org,
 kuniyu@...zon.com, bigeasy@...utronix.de
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 harini.katakam@....com, radhey.shyam.pandey@....com, michal.simek@....com
Subject: Re: [RFC PATCH net-next] net: Modify CSUM capability check for USO

On 3/12/25 12:54 PM, Radharapu Rakesh wrote:
>  net/core/dev.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 1cb134ff7327..a22f8f6e2ed1 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -10465,11 +10465,13 @@ static void netdev_sync_lower_features(struct net_device *upper,
>  
>  static bool netdev_has_ip_or_hw_csum(netdev_features_t features)
>  {
> -	netdev_features_t ip_csum_mask = NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM;
> -	bool ip_csum = (features & ip_csum_mask) == ip_csum_mask;
> +	netdev_features_t ipv4_csum_mask = NETIF_F_IP_CSUM;
> +	netdev_features_t ipv6_csum_mask = NETIF_F_IPV6_CSUM;
> +	bool ipv4_csum = (features & ipv4_csum_mask) == ipv4_csum_mask;
> +	bool ipv6_csum = (features & ipv6_csum_mask) == ipv6_csum_mask;
>  	bool hw_csum = features & NETIF_F_HW_CSUM;
>  
> -	return ip_csum || hw_csum;
> +	return ipv4_csum || ipv6_csum || hw_csum;
>  }

The above will additionally affect TLS offload, and will likely break
i.e. USO over IPv6 traffic landing on devices supporting only USO over
IPv4, unless such devices additionally implement a suitable
ndo_features_check().

Such situation will be quite bug prone, I'm unsure we want this kind of
change - even without looking at the TLS side of it.

/P