[PATCH v1] ibmveth: Set CHECKSUM_PARTIAL if NULL TCP CSUM.
From: David Wilder <hidden>
Date: 2021-06-22 21:53:00
TCP checksums on received packets may be set to NULL by the sender if CSO is enabled. The hypervisor flags these packets as check-sum-ok and the skb is then flagged CHECKSUM_UNNECESSARY. If these packets are then forwarded the sender will not request CSO due to the CHECKSUM_UNNECESSARY flag. The result is a TCP packet sent with a bad checksum. This change sets up CHECKSUM_PARTIAL on these packets causing the sender to correctly request CSUM offload. Signed-off-by: David Wilder <redacted> Reviewed-by: Pradeep Satyanarayana <redacted> Tested-by: Cristobal Forno <redacted> --- drivers/net/ethernet/ibm/ibmveth.c | 51 ++++++++++++++++-------------- 1 file changed, 28 insertions(+), 23 deletions(-)
diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c
index 7fea9ae60f13..da6c63ff2790 100644
--- a/drivers/net/ethernet/ibm/ibmveth.c
+++ b/drivers/net/ethernet/ibm/ibmveth.c@@ -1285,36 +1285,41 @@ static void ibmveth_rx_csum_helper(struct sk_buff *skb, iph_proto = iph6->nexthdr; } - /* In OVS environment, when a flow is not cached, specifically for a - * new TCP connection, the first packet information is passed up + /* When CSO is enabled the TCP checksum may have be set to NULL by + * the sender given that we zeroed out TCP checksum field in + * transmit path (refer ibmveth_start_xmit routine). In this case set + * up CHECKSUM_PARTIAL. If the packet is forwarded, the checksum will + * then be recalculated by the destination NIC (CSO must be enabled + * on the destination NIC). + * + * In an OVS environment, when a flow is not cached, specifically for a + * new TCP connection, the first packet information is passed up to * the user space for finding a flow. During this process, OVS computes * checksum on the first packet when CHECKSUM_PARTIAL flag is set. * - * Given that we zeroed out TCP checksum field in transmit path - * (refer ibmveth_start_xmit routine) as we set "no checksum bit", - * OVS computed checksum will be incorrect w/o TCP pseudo checksum - * in the packet. This leads to OVS dropping the packet and hence - * TCP retransmissions are seen. - * - * So, re-compute TCP pseudo header checksum. + * So, re-compute TCP pseudo header checksum when configured for + * trunk mode. */ - if (iph_proto == IPPROTO_TCP && adapter->is_active_trunk) { + if (iph_proto == IPPROTO_TCP) { struct tcphdr *tcph = (struct tcphdr *)(skb->data + iphlen); - - tcphdrlen = skb->len - iphlen; - - /* Recompute TCP pseudo header checksum */ - if (skb_proto == ETH_P_IP) - tcph->check = ~csum_tcpudp_magic(iph->saddr, + if (tcph->check == 0x0000) { + /* Recompute TCP pseudo header checksum */ + if (adapter->is_active_trunk) { + tcphdrlen = skb->len - iphlen; + if (skb_proto == ETH_P_IP) + tcph->check = + ~csum_tcpudp_magic(iph->saddr, iph->daddr, tcphdrlen, iph_proto, 0); - else if (skb_proto == ETH_P_IPV6) - tcph->check = ~csum_ipv6_magic(&iph6->saddr, + else if (skb_proto == ETH_P_IPV6) + tcph->check = + ~csum_ipv6_magic(&iph6->saddr, &iph6->daddr, tcphdrlen, iph_proto, 0); - - /* Setup SKB fields for checksum offload */ - skb_partial_csum_set(skb, iphlen, - offsetof(struct tcphdr, check)); - skb_reset_network_header(skb); + } + /* Setup SKB fields for checksum offload */ + skb_partial_csum_set(skb, iphlen, + offsetof(struct tcphdr, check)); + skb_reset_network_header(skb); + } } }
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2.27.0