[PATCH net-next 0/2] gue: Generalize remote checksum offload

[PATCH net-next 0/2] gue: Generalize remote checksum offload

[Tom Herbert]

The remote checksum offload is generalized by creating a common
function (remcsum_adjust) that does the work of modifying the
checksum in remote checksum offload. This function can be called
from normal or GRO path. GUE was modified to use this function.

Remote checksum offload is described in
https://tools.ietf.org/html/draft-herbert-remotecsumoffload-01

Tested by running 200 TCP_STREAM connections over GUE, did not see
any problems with remote checksum offload enabled.

Tom Herbert (2):
  net: Add remcsum_adjust as common function for remote checksum offload
  gue: Call remcsum_adjust

 include/net/checksum.h | 16 ++++++++++
 net/ipv4/fou.c         | 84 ++++++++++----------------------------------------
 2 files changed, 33 insertions(+), 67 deletions(-)

-- 
2.1.0.rc2.206.gedb03e5

[PATCH net-next 1/2] net: Add remcsum_adjust as common function for remote checksum offload

[Tom Herbert]

This function does the work to update a checksum field as part of
remote checksum offload.

remcsum_adjust does the following:

1) Subtract out the calculated checksum from the beginning of the
   packet (ptr arg) to the start offset.
2) Adjust the checksum field indicated by offset based on the modified
   checksum value from above step.
3) Return the difference in the old checksum field value and the
   new one. The caller will use this to update skb->csum and NAPI csum.

Signed-off-by: Tom Herbert <therbert@google.com>
---
 include/net/checksum.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/net/checksum.h b/include/net/checksum.h
index 6465bae..e339a95 100644
--- a/include/net/checksum.h
+++ b/include/net/checksum.h
@@ -151,4 +151,20 @@ static inline void inet_proto_csum_replace2(__sum16 *sum, struct sk_buff *skb,
 				 (__force __be32)to, pseudohdr);
 }
 
+static inline __wsum remcsum_adjust(void *ptr, __wsum csum,
+				    int start, int offset)
+{
+	__sum16 *psum = (__sum16 *)(ptr + offset);
+	__wsum delta;
+
+	/* Subtract out checksum up to start */
+	csum = csum_sub(csum, csum_partial(ptr, start, 0));
+
+	/* Set derived checksum in packet */
+	delta = csum_sub(csum_fold(csum), *psum);
+	*psum = csum_fold(csum);
+
+	return delta;
+}
+
 #endif
-- 
2.1.0.rc2.206.gedb03e5

[PATCH net-next 2/2] gue: Call remcsum_adjust

[Tom Herbert]

Change remote checksum offload to call remcsum_adjust. This also
eliminates the optimization to skip an IP header as part of the
adjustment (really does not seem to be much of a win).

Signed-off-by: Tom Herbert <therbert@google.com>
---
 net/ipv4/fou.c | 84 ++++++++++++----------------------------------------------
 1 file changed, 17 insertions(+), 67 deletions(-)

diff --git a/net/ipv4/fou.c b/net/ipv4/fou.c
index 3dfe982..b986298 100644
--- a/net/ipv4/fou.c
+++ b/net/ipv4/fou.c
@@ -64,15 +64,13 @@ static int fou_udp_recv(struct sock *sk, struct sk_buff *skb)
 }
 
 static struct guehdr *gue_remcsum(struct sk_buff *skb, struct guehdr *guehdr,
-				  void *data, int hdrlen, u8 ipproto)
+				  void *data, size_t hdrlen, u8 ipproto)
 {
 	__be16 *pd = data;
-	u16 start = ntohs(pd[0]);
-	u16 offset = ntohs(pd[1]);
-	u16 poffset = 0;
-	u16 plen;
-	__wsum csum, delta;
-	__sum16 *psum;
+	size_t start = ntohs(pd[0]);
+	size_t offset = ntohs(pd[1]);
+	size_t plen = hdrlen + max_t(size_t, offset + sizeof(u16), start);
+	__wsum delta;
 
 	if (skb->remcsum_offload) {
 		/* Already processed in GRO path */
@@ -80,35 +78,15 @@ static struct guehdr *gue_remcsum(struct sk_buff *skb, struct guehdr *guehdr,
 		return guehdr;
 	}
 
-	if (start > skb->len - hdrlen ||
-	    offset > skb->len - hdrlen - sizeof(u16))
-		return NULL;
-
-	if (unlikely(skb->ip_summed != CHECKSUM_COMPLETE))
-		__skb_checksum_complete(skb);
-
-	plen = hdrlen + offset + sizeof(u16);
 	if (!pskb_may_pull(skb, plen))
 		return NULL;
 	guehdr = (struct guehdr *)&udp_hdr(skb)[1];
 
-	if (ipproto == IPPROTO_IP && sizeof(struct iphdr) < plen) {
-		struct iphdr *ip = (struct iphdr *)(skb->data + hdrlen);
-
-		/* If next header happens to be IP we can skip that for the
-		 * checksum calculation since the IP header checksum is zero
-		 * if correct.
-		 */
-		poffset = ip->ihl * 4;
-	}
-
-	csum = csum_sub(skb->csum, skb_checksum(skb, poffset + hdrlen,
-						start - poffset - hdrlen, 0));
+	if (unlikely(skb->ip_summed != CHECKSUM_COMPLETE))
+		__skb_checksum_complete(skb);
 
-	/* Set derived checksum in packet */
-	psum = (__sum16 *)(skb->data + hdrlen + offset);
-	delta = csum_sub(csum_fold(csum), *psum);
-	*psum = csum_fold(csum);
+	delta = remcsum_adjust((void *)guehdr + hdrlen,
+			       skb->csum, start, offset);
 
 	/* Adjust skb->csum since we changed the packet */
 	skb->csum = csum_add(skb->csum, delta);
@@ -158,9 +136,6 @@ static int gue_udp_recv(struct sock *sk, struct sk_buff *skb)
 
 	ip_hdr(skb)->tot_len = htons(ntohs(ip_hdr(skb)->tot_len) - len);
 
-	/* Pull UDP header now, skb->data points to guehdr */
-	__skb_pull(skb, sizeof(struct udphdr));
-
 	/* Pull csum through the guehdr now . This can be used if
 	 * there is a remote checksum offload.
 	 */
@@ -188,7 +163,7 @@ static int gue_udp_recv(struct sock *sk, struct sk_buff *skb)
 	if (unlikely(guehdr->control))
 		return gue_control_message(skb, guehdr);
 
-	__skb_pull(skb, hdrlen);
+	__skb_pull(skb, sizeof(struct udphdr) + hdrlen);
 	skb_reset_transport_header(skb);
 
 	return -guehdr->proto_ctype;
@@ -248,24 +223,17 @@ static struct guehdr *gue_gro_remcsum(struct sk_buff *skb, unsigned int off,
 				      size_t hdrlen, u8 ipproto)
 {
 	__be16 *pd = data;
-	u16 start = ntohs(pd[0]);
-	u16 offset = ntohs(pd[1]);
-	u16 poffset = 0;
-	u16 plen;
-	void *ptr;
-	__wsum csum, delta;
-	__sum16 *psum;
+	size_t start = ntohs(pd[0]);
+	size_t offset = ntohs(pd[1]);
+	size_t plen = hdrlen + max_t(size_t, offset + sizeof(u16), start);
+	__wsum delta;
 
 	if (skb->remcsum_offload)
 		return guehdr;
 
-	if (start > skb_gro_len(skb) - hdrlen ||
-	    offset > skb_gro_len(skb) - hdrlen - sizeof(u16) ||
-	    !NAPI_GRO_CB(skb)->csum_valid || skb->remcsum_offload)
+	if (!NAPI_GRO_CB(skb)->csum_valid)
 		return NULL;
 
-	plen = hdrlen + offset + sizeof(u16);
-
 	/* Pull checksum that will be written */
 	if (skb_gro_header_hard(skb, off + plen)) {
 		guehdr = skb_gro_header_slow(skb, off + plen, off);
@@ -273,26 +241,8 @@ static struct guehdr *gue_gro_remcsum(struct sk_buff *skb, unsigned int off,
 			return NULL;
 	}
 
-	ptr = (void *)guehdr + hdrlen;
-
-	if (ipproto == IPPROTO_IP &&
-	    (hdrlen + sizeof(struct iphdr) < plen)) {
-		struct iphdr *ip = (struct iphdr *)(ptr + hdrlen);
-
-		/* If next header happens to be IP we can skip
-		 * that for the checksum calculation since the
-		 * IP header checksum is zero if correct.
-		 */
-		poffset = ip->ihl * 4;
-	}
-
-	csum = csum_sub(NAPI_GRO_CB(skb)->csum,
-			csum_partial(ptr + poffset, start - poffset, 0));
-
-	/* Set derived checksum in packet */
-	psum = (__sum16 *)(ptr + offset);
-	delta = csum_sub(csum_fold(csum), *psum);
-	*psum = csum_fold(csum);
+	delta = remcsum_adjust((void *)guehdr + hdrlen,
+			       NAPI_GRO_CB(skb)->csum, start, offset);
 
 	/* Adjust skb->csum since we changed the packet */
 	skb->csum = csum_add(skb->csum, delta);
-- 
2.1.0.rc2.206.gedb03e5

Re: [PATCH net-next 0/2] gue: Generalize remote checksum offload

[David Miller]

From: Tom Herbert <therbert@google.com>
Date: Tue, 25 Nov 2014 11:21:18 -0800

> The remote checksum offload is generalized by creating a common
> function (remcsum_adjust) that does the work of modifying the
> checksum in remote checksum offload. This function can be called
> from normal or GRO path. GUE was modified to use this function.
> 
> Remote checksum offload is described in
> https://tools.ietf.org/html/draft-herbert-remotecsumoffload-01
> 
> Tested by running 200 TCP_STREAM connections over GUE, did not see
> any problems with remote checksum offload enabled.

Series applied, thanks Tom.