gso: Support partial splitting at the frag_list pointer

Since commit 8a29111c7 ("net: gro: allow to build full sized skb")
gro may build buffers with a frag_list. This can hurt forwarding
because most NICs can't offload such packets, they need to be
segmented in software. This patch splits buffers with a frag_list
at the frag_list pointer into buffers that can be TSO offloaded.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 40 insertions, 11 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 1e329d411242..7bf82a28e10a 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3097,11 +3097,31 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
 	sg = !!(features & NETIF_F_SG);
 	csum = !!can_checksum_protocol(features, proto);
 
-	/* GSO partial only requires that we trim off any excess that
-	 * doesn't fit into an MSS sized block, so take care of that
-	 * now.
-	 */
-	if (sg && csum && (features & NETIF_F_GSO_PARTIAL)) {
+	if (sg && csum && (mss != GSO_BY_FRAGS))  {
+		if (!(features & NETIF_F_GSO_PARTIAL)) {
+			struct sk_buff *iter;
+
+			if (!list_skb ||
+			    !net_gso_ok(features, skb_shinfo(head_skb)->gso_type))
+				goto normal;
+
+			/* Split the buffer at the frag_list pointer.
+			 * This is based on the assumption that all
+			 * buffers in the chain excluding the last
+			 * containing the same amount of data.
+			 */
+			skb_walk_frags(head_skb, iter) {
+				if (skb_headlen(iter))
+					goto normal;
+
+				len -= iter->len;
+			}
+		}
+
+		/* GSO partial only requires that we trim off any excess that
+		 * doesn't fit into an MSS sized block, so take care of that
+		 * now.
+		 */
 		partial_segs = len / mss;
 		if (partial_segs > 1)
 			mss *= partial_segs;
@@ -3109,6 +3129,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
 			partial_segs = 0;
 	}
 
+normal:
 	headroom = skb_headroom(head_skb);
 	pos = skb_headlen(head_skb);
 
@@ -3300,21 +3321,29 @@ perform_csum_check:
 	 */
 	segs->prev = tail;
 
-	/* Update GSO info on first skb in partial sequence. */
 	if (partial_segs) {
+		struct sk_buff *iter;
 		int type = skb_shinfo(head_skb)->gso_type;
+		unsigned short gso_size = skb_shinfo(head_skb)->gso_size;
 
 		/* Update type to add partial and then remove dodgy if set */
-		type |= SKB_GSO_PARTIAL;
+		type |= (features & NETIF_F_GSO_PARTIAL) / NETIF_F_GSO_PARTIAL * SKB_GSO_PARTIAL;
 		type &= ~SKB_GSO_DODGY;
 
 		/* Update GSO info and prepare to start updating headers on
 		 * our way back down the stack of protocols.
 		 */
-		skb_shinfo(segs)->gso_size = skb_shinfo(head_skb)->gso_size;
-		skb_shinfo(segs)->gso_segs = partial_segs;
-		skb_shinfo(segs)->gso_type = type;
-		SKB_GSO_CB(segs)->data_offset = skb_headroom(segs) + doffset;
+		for (iter = segs; iter; iter = iter->next) {
+			skb_shinfo(iter)->gso_size = gso_size;
+			skb_shinfo(iter)->gso_segs = partial_segs;
+			skb_shinfo(iter)->gso_type = type;
+			SKB_GSO_CB(iter)->data_offset = skb_headroom(iter) + doffset;
+		}
+
+		if (tail->len - doffset <= gso_size)
+			skb_shinfo(tail)->gso_size = 0;
+		else if (tail != segs)
+			skb_shinfo(tail)->gso_segs = DIV_ROUND_UP(tail->len - doffset, gso_size);
 	}
 
 	/* Following permits correct backpressure, for protocols