Currently, the VIRTIO_NET_F_GUEST_CSUM (corresponds to NETIF_F_RXCSUM
for netdev) feature of the virtio-net driver conflicts with the loading
of XDP, which is caused by the problem described in [1][2], that is,
XDP may cause errors in partial csumed-related fields which can lead
to packet dropping.
In addition, when communicating between vm and vm on the same host, the
receiving side vm will receive packets marked as
VIRTIO_NET_HDR_F_NEEDS_CSUM, but after these packets are processed by
XDP, the VIRTIO_NET_HDR_F_NEEDS_CSUM and skb CHECKSUM_PARTIAL flags will
be cleared, causing the packet dropping.
This patch introduces a helper:
1. It will try to solve the above problems in the subsequent patch.
2. It parses UDP/TCP and calculates the pseudo-header checksum
for virtio-net. virtio-net currently does not resolve VLANs nor
SCTP CRC checksum offloading.
[1] commit 18ba58e1c234 ("virtio-net: fail XDP set if guest csum is negotiated")
[2] commit e59ff2c49ae1 ("virtio-net: disable guest csum during XDP set")
Signed-off-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
Reviewed-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
drivers/net/virtio_net.c | 136 +++++++++++++++++++++++++++++++++++++++
1 file changed, 136 insertions(+)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 5a7f7a76b920..83ab9257043a 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -22,6 +22,7 @@
#include <net/route.h>
#include <net/xdp.h>
#include <net/net_failover.h>
+#include <net/ip6_checksum.h>
static int napi_weight = NAPI_POLL_WEIGHT;
module_param(napi_weight, int, 0444);
@@ -1568,6 +1569,141 @@ static void virtio_skb_set_hash(const struct virtio_net_hdr_v1_hash *hdr_hash,
skb_set_hash(skb, __le32_to_cpu(hdr_hash->hash_value), rss_hash_type);
}
+static int virtnet_flow_dissect_udp_tcp(struct virtnet_info *vi, struct sk_buff *skb)
+{
+ struct net_device *dev = vi->dev;
+ struct flow_keys_basic keys;
+ struct udphdr *uh;
+ struct tcphdr *th;
+ int len, offset;
+
+ /* The flow dissector needs this information. */
+ skb->dev = dev;
+ skb_reset_mac_header(skb);
+ skb->protocol = dev_parse_header_protocol(skb);
+ /* virtio-net does not need to resolve VLAN. */
+ skb_set_network_header(skb, ETH_HLEN);
+ if (!skb_flow_dissect_flow_keys_basic(NULL, skb, &keys,
+ NULL, 0, 0, 0, 0))
+ return -EINVAL;
+
+ /* 1. Pseudo-header checksum calculation requires:
+ * (1) saddr/daddr (2) IP_PROTO (3) length of transport payload
+ * 2. We don't parse SCTP because virtio-net currently doesn't
+ * support CRC checksum offloading for SCTP.
+ */
+ if (keys.basic.n_proto == htons(ETH_P_IP)) {
+ struct iphdr *iph;
+
+ /* Flow dissector has verified that there is an IP header.
+ * So we do not need a pskb_may_pull().
+ */
+ iph = ip_hdr(skb);
+ if (iph->version != 4)
+ return -EINVAL;
+
+ skb->transport_header = skb->mac_header + keys.control.thoff;
+ offset = skb_transport_offset(skb);
+ len = skb->len - offset;
+ if (keys.basic.ip_proto == IPPROTO_UDP) {
+ if (!pskb_may_pull(skb, offset + sizeof(struct udphdr)))
+ return -EINVAL;
+
+ uh = udp_hdr(skb);
+ skb->csum_offset = offsetof(struct udphdr, check);
+ /* Although uh->len is already the 3rd parameter for the calculation
+ * of the pseudo-header checksum, we have already calculated the
+ * length of the transport layer, so use 'len' here directly.
+ */
+ uh->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr, len,
+ IPPROTO_UDP, 0);
+ } else if (keys.basic.ip_proto == IPPROTO_TCP) {
+ if (!pskb_may_pull(skb, offset + sizeof(struct tcphdr)))
+ return -EINVAL;
+
+ th = tcp_hdr(skb);
+ skb->csum_offset = offsetof(struct tcphdr, check);
+ th->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr, len,
+ IPPROTO_TCP, 0);
+ } /* virtio-net doesn't support checksums for SCTP crc hw offloading.*/
+ } else if (keys.basic.n_proto == htons(ETH_P_IPV6)) {
+ struct ipv6hdr *ip6h;
+
+ ip6h = ipv6_hdr(skb);
+ if (ip6h->version != 6)
+ return -EINVAL;
+
+ /* We have skipped the possible extension headers for IPv6.
+ * If there is a Routing Header, the tx's check value is calculated by
+ * final_dst, and that value is the rx's daddr.
+ */
+ skb->transport_header = skb->mac_header + keys.control.thoff;
+ offset = skb_transport_offset(skb);
+ len = skb->len - offset;
+ if (keys.basic.ip_proto == IPPROTO_UDP) {
+ if (!pskb_may_pull(skb, offset + sizeof(struct udphdr)))
+ return -EINVAL;
+
+ uh = udp_hdr(skb);
+ skb->csum_offset = offsetof(struct udphdr, check);
+ uh->check = ~csum_ipv6_magic((const struct in6_addr *)&ip6h->saddr,
+ (const struct in6_addr *)&ip6h->daddr,
+ len, IPPROTO_UDP, 0);
+ } else if (keys.basic.ip_proto == IPPROTO_TCP) {
+ if (!pskb_may_pull(skb, offset + sizeof(struct tcphdr)))
+ return -EINVAL;
+
+ th = tcp_hdr(skb);
+ skb->csum_offset = offsetof(struct tcphdr, check);
+ th->check = ~csum_ipv6_magic((const struct in6_addr *)&ip6h->saddr,
+ (const struct in6_addr *)&ip6h->daddr,
+ len, IPPROTO_TCP, 0);
+ }
+ }
+
+ skb->csum_start = skb->transport_header;
+
+ return 0;
+}
+
+static int virtnet_set_csum_after_xdp(struct virtnet_info *vi,
+ struct sk_buff *skb,
+ __u8 flags)
+{
+ int err;
+
+ /* When XDP program is loaded, for example, the vm-vm scenario
+ * on the same host, packets marked as VIRTIO_NET_HDR_F_NEEDS_CSUM
+ * will travel. Although these packets are safe from the point of
+ * view of the vm, to avoid modification by XDP and successful
+ * forwarding in the upper layer, we re-probe the necessary checksum
+ * related information: skb->csum_{start, offset}, pseudo-header csum.
+ *
+ * This benefits us:
+ * 1. XDP can be loaded when there's _F_GUEST_CSUM.
+ * 2. The device verifies the checksum of packets , especially
+ * benefiting for large packets.
+ * 3. In the same-host vm-vm scenario, packets marked as
+ * VIRTIO_NET_HDR_F_NEEDS_CSUM are no longer dropped after being
+ * processed by XDP.
+ */
+ if (flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
+ err = virtnet_flow_dissect_udp_tcp(vi, skb);
+ if (err < 0)
+ return -EINVAL;
+
+ skb->ip_summed = CHECKSUM_PARTIAL;
+ } else if (flags & VIRTIO_NET_HDR_F_DATA_VALID) {
+ /* We want to benefit from this: XDP guarantees that packets marked
+ * as VIRTIO_NET_HDR_F_DATA_VALID still have correct csum after they
+ * are processed.
+ */
+ skb->ip_summed = CHECKSUM_UNNECESSARY;
+ }
+
+ return 0;
+}
+
static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
void *buf, unsigned int len, void **ctx,
unsigned int *xdp_xmit,
--
2.19.1.6.gb485710b
