netdev - Re: [PATCH net-next v2] udp: Avoid post-GRO UDP checksum recalculation

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Date:   Thu, 30 May 2019 11:10:55 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     stranche@...eaurora.org
Cc:     netdev@...r.kernel.org, pabeni@...hat.com, subashab@...eaurora.org
Subject: Re: [PATCH net-next v2] udp: Avoid post-GRO UDP checksum
 recalculation

From: Sean Tranchetti <stranche@...eaurora.org>
Date: Tue, 28 May 2019 12:22:54 -0600

> Currently, when resegmenting an unexpected UDP GRO packet, the full UDP
> checksum will be calculated for every new SKB created by skb_segment()
> because the netdev features passed in by udp_rcv_segment() lack any
> information about checksum offload capabilities.
> 
> Usually, we have no need to perform this calculation again, as
>   1) The GRO implementation guarantees that any packets making it to the
>      udp_rcv_segment() function had correct checksums, and, more
>      importantly,
>   2) Upon the successful return of udp_rcv_segment(), we immediately pull
>      the UDP header off and either queue the segment to the socket or
>      hand it off to a new protocol handler.
> 
> Unless userspace has set the IP_CHECKSUM sockopt to indicate that they
> want the final checksum values, we can pass the needed netdev feature
> flags to __skb_gso_segment() to avoid checksumming each segment in
> skb_segment().
> 
> Fixes: cf329aa42b66 ("udp: cope with UDP GRO packet misdirection")
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
> Signed-off-by: Sean Tranchetti <stranche@...eaurora.org>

I've decided to apply this to 'net', thank you.