Metadata destinations were introduced in commit f38a9eb1f77b
("dst: Metadata destinations") to "carry per packet metadata
between forwarding and processing elements via the skb->dst pointer".
The aim of this new METADATA_SK_PREFETCH destination type is to allow
early forwarding elements to store a socket destination for the duration
of receiving into the IP stack, which can be later be identified to
avoid orphaning the skb and losing the prefetched socket in ip_rcv_core().
The destination is stored temporarily in a per-CPU buffer to ensure that
if applications attempt to reach out from loopback address to loopback
address, they may restore the original destination and avoid martian
packet drops.
Signed-off-by: Joe Stringer <joe@xxxxxxxxxxx>
---
include/net/dst_metadata.h | 31 +++++++++++++++++++++++++++++++
net/core/dst.c | 30 ++++++++++++++++++++++++++++++
2 files changed, 61 insertions(+)
diff --git a/include/net/dst_metadata.h b/include/net/dst_metadata.h
index 56cb3c38569a..31574c553a07 100644
--- a/include/net/dst_metadata.h
+++ b/include/net/dst_metadata.h
@@ -9,6 +9,7 @@
enum metadata_type {
METADATA_IP_TUNNEL,
METADATA_HW_PORT_MUX,
+ METADATA_SK_PREFETCH,
};
struct hw_port_info {
@@ -80,6 +81,8 @@ static inline int skb_metadata_dst_cmp(const struct sk_buff *skb_a,
return memcmp(&a->u.tun_info, &b->u.tun_info,
sizeof(a->u.tun_info) +
a->u.tun_info.options_len);
+ case METADATA_SK_PREFETCH:
+ return 0;
default:
return 1;
}
@@ -214,4 +217,32 @@ static inline struct metadata_dst *ipv6_tun_rx_dst(struct sk_buff *skb,
0, ip6_flowlabel(ip6h), flags, tunnel_id,
md_size);
}
+
+extern const struct metadata_dst dst_sk_prefetch;
+
+static inline bool dst_is_sk_prefetch(const struct dst_entry *dst)
+{
+ return dst == &dst_sk_prefetch.dst;
+}
+
+static inline bool skb_dst_is_sk_prefetch(const struct sk_buff *skb)
+{
+ return dst_is_sk_prefetch(skb_dst(skb));
+}
+
+void dst_sk_prefetch_store(struct sk_buff *skb);
+void dst_sk_prefetch_fetch(struct sk_buff *skb);
+
+/**
+ * dst_sk_prefetch_reset - reset prefetched socket dst
+ * @skb: buffer
+ *
+ * Reverts the dst back to the originally stored dst if present.
+ */
+static inline void dst_sk_prefetch_reset(struct sk_buff *skb)
+{
+ if (unlikely(skb_dst_is_sk_prefetch(skb)))
+ dst_sk_prefetch_fetch(skb);
+}
+
#endif /* __NET_DST_METADATA_H */
diff --git a/net/core/dst.c b/net/core/dst.c
index 193af526e908..cf1a1d5b6b0a 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -330,3 +330,33 @@ void metadata_dst_free_percpu(struct metadata_dst __percpu *md_dst)
free_percpu(md_dst);
}
EXPORT_SYMBOL_GPL(metadata_dst_free_percpu);
+
+const struct metadata_dst dst_sk_prefetch = {
+ .dst = {
+ .ops = &md_dst_ops,
+ .input = dst_md_discard,
+ .output = dst_md_discard_out,
+ .flags = DST_NOCOUNT | DST_METADATA,
+ .obsolete = DST_OBSOLETE_NONE,
+ .__refcnt = ATOMIC_INIT(1),
+ },
+ .type = METADATA_SK_PREFETCH,
+};
+EXPORT_SYMBOL(dst_sk_prefetch);
+
+DEFINE_PER_CPU(unsigned long, dst_sk_prefetch_dst);
+
+void dst_sk_prefetch_store(struct sk_buff *skb)
+{
+ unsigned long refdst;
+
+ refdst = skb->_skb_refdst;
+ __this_cpu_write(dst_sk_prefetch_dst, refdst);
+ skb_dst_set_noref(skb, (struct dst_entry *)&dst_sk_prefetch.dst);
+}
+
+void dst_sk_prefetch_fetch(struct sk_buff *skb)
+{
+ skb->_skb_refdst = __this_cpu_read(dst_sk_prefetch_dst);
+}
+EXPORT_SYMBOL(dst_sk_prefetch_fetch);
--
2.20.1
