[PATCH net-next 3/4] gve: pull network headers into skb linear part

[Joshua Washington <joshwash@google.com>]

From: Ankit Garg <nktgrg@google.com>

Currently, in DQO mode with hw-gro enabled, entire received packet is
placed into skb fragments when header-split is disabled. This leaves
the skb linear part empty, forcing the networking stack to do multiple
small memory copies to access eth, IP and TCP headers.

This patch adds a single memcpy to put all headers into linear portion
before packet reaches the SW GRO stack; thus eliminating multiple
smaller memcpy calls.

Additionally, the criteria for calling napi_gro_frags() was updated.
Since skb->head is now populated, we instead check if the SKB is the
cached NAPI scratchpad to ensure we continue using the zero-allocation
path.

Signed-off-by: Ankit Garg <nktgrg@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
Signed-off-by: Joshua Washington <joshwash@google.com>
---
 drivers/net/ethernet/google/gve/gve_rx_dqo.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve_rx_dqo.c b/drivers/net/ethernet/google/gve/gve_rx_dqo.c
index 5ba893e5..ac44f50d 100644
--- a/drivers/net/ethernet/google/gve/gve_rx_dqo.c
+++ b/drivers/net/ethernet/google/gve/gve_rx_dqo.c
@@ -946,6 +946,8 @@ static int gve_rx_complete_rsc(struct sk_buff *skb,
 {
 	struct skb_shared_info *shinfo = skb_shinfo(skb);
 	int rsc_segments, rsc_seg_len, hdr_len;
+	skb_frag_t *frag;
+	void *va;
 
 	/* HW-GRO only coalesces TCP. */
 	if (ptype.l4_type != GVE_L4_TYPE_TCP)
@@ -973,10 +975,20 @@ static int gve_rx_complete_rsc(struct sk_buff *skb,
 		/* HW-GRO packets are guaranteed to have complete TCP/IP
 		 * headers in frag[0] when header-split is not enabled.
 		 */
-		hdr_len = eth_get_headlen(skb->dev,
-					  skb_frag_address(&shinfo->frags[0]),
-					  skb_frag_size(&shinfo->frags[0]));
+		frag = &skb_shinfo(skb)->frags[0];
+		va = skb_frag_address(frag);
+		hdr_len =
+			eth_get_headlen(skb->dev, va, skb_frag_size(frag));
 		rsc_segments = DIV_ROUND_UP(skb->len - hdr_len, rsc_seg_len);
+		skb_copy_to_linear_data(skb, va, hdr_len);
+		skb_frag_size_sub(frag, hdr_len);
+		/* Verify we didn't empty the fragment completely as that could
+		 * otherwise lead to page leaks.
+		 */
+		DEBUG_NET_WARN_ON_ONCE(!skb_frag_size(frag));
+		skb_frag_off_add(frag, hdr_len);
+		skb->data_len -= hdr_len;
+		skb->tail += hdr_len;
 	}
 	shinfo->gso_size = rsc_seg_len;
 	shinfo->gso_segs = rsc_segments;
@@ -1013,7 +1025,7 @@ static int gve_rx_complete_skb(struct gve_rx_ring *rx, struct napi_struct *napi,
 			return err;
 	}
 
-	if (skb_headlen(rx->ctx.skb_head) == 0)
+	if (rx->ctx.skb_head == napi->skb)
 		napi_gro_frags(napi);
 	else
 		napi_gro_receive(napi, rx->ctx.skb_head);
-- 
2.53.0.473.g4a7958ca14-goog