From: Stephen Hemminger <stephen@networkplumber.org>
To: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
Cc: dev@dpdk.org
Subject: Re: [PATCH] net: fix cksum calculation for odd-sized segment
Date: Mon, 17 Aug 2026 19:16:52 -0700 [thread overview]
Message-ID: <20260817191652.108068ac@phoenix.local> (raw)
In-Reply-To: <20260813202236.246588-1-eva.kurchatova@virtuozzo.com>
On Thu, 13 Aug 2026 23:22:35 +0300
Eva Kurchatova <eva.kurchatova@virtuozzo.com> wrote:
> The rte_raw_cksum_mbuf() performs rte_bswap16() on return value from
> __rte_raw_cksum() for odd-sized segments. However, __rte_raw_cksum()
> returns a 32-bit accumulator whose upper 16 bits may still contain
> carries that must be folded. Truncating those upper bits by passing to
> rte_bswap16() will produce an invalid checksum if they are non-zero.
>
> This is surely a rare encounter in practice, as most NICs have hardware
> checksum offloads, and even then encountering an odd-sized SG segment
> is not common, but currently such a case would miscompute the checksum.
>
> I found this issue by accident when comparing RVVM networking stack
> packet checksuming to DPDK, and noticed that this looked incorrect.
>
> Fix this by folding the odd-sized segment checksum before bswap16.
>
> Signed-off-by: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
prev parent reply other threads:[~2026-08-18 2:17 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-13 20:22 [PATCH] net: fix cksum calculation for odd-sized segment Eva Kurchatova
2026-08-18 2:16 ` Stephen Hemminger [this message]
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