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Tue, 27 Oct 2026 19:50:42 -0700 (PDT) Received: from localhost.localdomain ([240e:46d:1d00:2b84:48c6:402f:d1c5:644a]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ae55d64c0bsm812447a91.1.2026.10.27.19.50.38 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Tue, 27 Oct 2026 19:50:41 -0700 (PDT) From: Rongzheng Wang To: netdev@vger.kernel.org Cc: Maciej Fijalkowski , Magnus Karlsson , Jason Xing , Stanislav Fomichev , Jesper Dangaard Brouer , stable@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Rongzheng Wang Subject: [PATCH net v3 1/2] xsk: defer software checksum until the skb is complete Date: Wed, 28 Oct 2026 10:50:25 +0800 Message-Id: <20261028025026.11401-2-testwrzwrz@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20261028025026.11401-1-testwrzwrz@gmail.com> References: <20261028025026.11401-1-testwrzwrz@gmail.com> X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When XDP_UMEM_TX_SW_CSUM is used with multi-buffer TX, xsk_skb_metadata() calls skb_checksum_help() while only the first descriptor has been added to the skb. The checksum therefore covers just the first fragment, and skb_checksum_help() sets ip_summed to CHECKSUM_NONE, so the remaining fragments are never included in the checksum. Move the software checksum calculation to the point where the last descriptor has been added to the skb. On a checksum failure the packet is now dropped instead of being returned to the application for a retry. This path is not reachable with the existing metadata validation, but the behavior change is intentional. Fixes: 11614723af26 ("xsk: Add option to calculate TX checksum in SW") Cc: stable@vger.kernel.org Signed-off-by: Rongzheng Wang --- net/xdp/xsk.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-) diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index 33475b180ea6..aa6b010192ad 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -1011,14 +1011,6 @@ static int xsk_skb_metadata(struct sk_buff *skb, void *buffer, skb->csum_start = hr + csum_start; skb->csum_offset = csum_offset; skb->ip_summed = CHECKSUM_PARTIAL; - - if (unlikely(pool->tx_sw_csum)) { - int err; - - err = skb_checksum_help(skb); - if (err) - return err; - } } if (flags & XDP_TXMD_FLAGS_LAUNCH_TIME) @@ -1030,6 +1022,15 @@ static int xsk_skb_metadata(struct sk_buff *skb, void *buffer, return 0; } +static int xsk_skb_sw_csum(struct sk_buff *skb, struct xsk_buff_pool *pool) +{ + if (unlikely(pool->tx_sw_csum && + skb->ip_summed == CHECKSUM_PARTIAL)) + return skb_checksum_help(skb); + + return 0; +} + static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs, struct xdp_desc *desc) { @@ -1275,6 +1276,12 @@ static int __xsk_generic_xmit(struct sock *sk) if (xp_mb_desc(&desc)) { xs->skb = skb; continue; + } else { + err = xsk_skb_sw_csum(skb, xs->pool); + if (unlikely(err)) { + xsk_drop_skb(skb); + goto out; + } } err = __dev_direct_xmit(skb, xs->queue_id); -- 2.39.5 (Apple Git-154)