net: Only do flow_dissector hash computation once per packet

Add sw_hash flag to skbuff to indicate that skb->hash was computed
from flow_dissector. This flag is checked in skb_get_hash to avoid
repeatedly trying to compute the hash (ie. in the case that no L4 hash
can be computed).

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 9 insertions, 2 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index b297af70ac30..890fb3307dd6 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -455,6 +455,7 @@ static inline u32 skb_mstamp_us_delta(const struct skb_mstamp *t1,
  *      @ooo_okay: allow the mapping of a socket to a queue to be changed
  *      @l4_hash: indicate hash is a canonical 4-tuple hash over transport
  *              ports.
+ *      @sw_hash: indicates hash was computed in software stack
  *      @wifi_acked_valid: wifi_acked was set
  *      @wifi_acked: whether frame was acked on wifi or not
  *      @no_fcs:  Request NIC to treat last 4 bytes as Ethernet FCS
@@ -562,6 +563,7 @@ struct sk_buff {
         __u8                    pfmemalloc:1;
         __u8                    ooo_okay:1;
         __u8                    l4_hash:1;
+        __u8                    sw_hash:1;
         __u8                    wifi_acked_valid:1;
         __u8                    wifi_acked:1;
         __u8                    no_fcs:1;
@@ -575,7 +577,7 @@ struct sk_buff {
         __u8                    encap_hdr_csum:1;
         __u8                    csum_valid:1;
         __u8                    csum_complete_sw:1;
-        /* 3/5 bit hole (depending on ndisc_nodetype presence) */
+        /* 2/4 bit hole (depending on ndisc_nodetype presence) */
         kmemcheck_bitfield_end(flags2);
 
 #if defined CONFIG_NET_DMA || defined CONFIG_NET_RX_BUSY_POLL
@@ -830,13 +832,14 @@ static inline void
 skb_set_hash(struct sk_buff *skb, __u32 hash, enum pkt_hash_types type)
 {
         skb->l4_hash = (type == PKT_HASH_TYPE_L4);
+        skb->sw_hash = 0;
         skb->hash = hash;
 }
 
 void __skb_get_hash(struct sk_buff *skb);
 static inline __u32 skb_get_hash(struct sk_buff *skb)
 {
-        if (!skb->l4_hash)
+        if (!skb->l4_hash && !skb->sw_hash)
                 __skb_get_hash(skb);
 
         return skb->hash;
@@ -850,6 +853,7 @@ static inline __u32 skb_get_hash_raw(const struct sk_buff *skb)
 static inline void skb_clear_hash(struct sk_buff *skb)
 {
         skb->hash = 0;
+        skb->sw_hash = 0;
         skb->l4_hash = 0;
 }
 
@@ -862,6 +866,7 @@ static inline void skb_clear_hash_if_not_l4(struct sk_buff *skb)
 static inline void skb_copy_hash(struct sk_buff *to, const struct sk_buff *from)
 {
         to->hash = from->hash;
+        to->sw_hash = from->sw_hash;
         to->l4_hash = from->l4_hash;
 };
 
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index c5f3912dad4c..5f362c1d0332 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -256,6 +256,8 @@ void __skb_get_hash(struct sk_buff *skb)
         if (keys.ports)
                 skb->l4_hash = 1;
 
+        skb->sw_hash = 1;
+
         skb->hash = __flow_hash_from_keys(&keys);
 }
 EXPORT_SYMBOL(__skb_get_hash);