netdev - [PATCH net v2] gve: Secure enough bytes in the first TX desc for all TCP pkts

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Message-ID: <20230403172809.2939306-1-shailend@google.com>
Date:   Mon,  3 Apr 2023 10:28:09 -0700
From:   Shailend Chand <shailend@...gle.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org,
        Shailend Chand <shailend@...gle.com>
Subject: [PATCH net v2] gve: Secure enough bytes in the first TX desc for all
 TCP pkts

Non-GSO TCP packets whose SKBs' linear portion did not include the
entire TCP header were not populating the first Tx descriptor with
as many bytes as the vNIC expected. This change ensures that all
TCP packets populate the first descriptor with the correct number of
bytes.

Fixes: 893ce44df565 ("gve: Add basic driver framework for Compute Engine Virtual NIC")
Signed-off-by: Shailend Chand <shailend@...gle.com>
---
Changes in v2:
  - Clarify that the spec being mentioned is the gVNIC spec
  - Add a define for the "182" magic number

 drivers/net/ethernet/google/gve/gve.h    |  2 ++
 drivers/net/ethernet/google/gve/gve_tx.c | 12 +++++-------
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve.h b/drivers/net/ethernet/google/gve/gve.h
index 64eb0442c82f..005cb9dfe078 100644
--- a/drivers/net/ethernet/google/gve/gve.h
+++ b/drivers/net/ethernet/google/gve/gve.h
@@ -47,6 +47,8 @@
 
 #define GVE_RX_BUFFER_SIZE_DQO 2048
 
+#define GVE_GQ_TX_MIN_PKT_DESC_BYTES 182
+
 /* Each slot in the desc ring has a 1:1 mapping to a slot in the data ring */
 struct gve_rx_desc_queue {
 	struct gve_rx_desc *desc_ring; /* the descriptor ring */
diff --git a/drivers/net/ethernet/google/gve/gve_tx.c b/drivers/net/ethernet/google/gve/gve_tx.c
index 4888bf05fbed..5e11b8236754 100644
--- a/drivers/net/ethernet/google/gve/gve_tx.c
+++ b/drivers/net/ethernet/google/gve/gve_tx.c
@@ -284,8 +284,8 @@ static inline int gve_skb_fifo_bytes_required(struct gve_tx_ring *tx,
 	int bytes;
 	int hlen;
 
-	hlen = skb_is_gso(skb) ? skb_checksum_start_offset(skb) +
-				 tcp_hdrlen(skb) : skb_headlen(skb);
+	hlen = skb_is_gso(skb) ? skb_checksum_start_offset(skb) + tcp_hdrlen(skb) :
+				 min_t(int, GVE_GQ_TX_MIN_PKT_DESC_BYTES, skb->len);
 
 	pad_bytes = gve_tx_fifo_pad_alloc_one_frag(&tx->tx_fifo,
 						   hlen);
@@ -454,13 +454,11 @@ static int gve_tx_add_skb_copy(struct gve_priv *priv, struct gve_tx_ring *tx, st
 	pkt_desc = &tx->desc[idx];
 
 	l4_hdr_offset = skb_checksum_start_offset(skb);
-	/* If the skb is gso, then we want the tcp header in the first segment
-	 * otherwise we want the linear portion of the skb (which will contain
-	 * the checksum because skb->csum_start and skb->csum_offset are given
-	 * relative to skb->head) in the first segment.
+	/* If the skb is gso, then we want the tcp header alone in the first segment
+	 * otherwise we want the minimum required by the gVNIC spec.
 	 */
 	hlen = is_gso ? l4_hdr_offset + tcp_hdrlen(skb) :
-			skb_headlen(skb);
+			min_t(int, GVE_GQ_TX_MIN_PKT_DESC_BYTES, skb->len);
 
 	info->skb =  skb;
 	/* We don't want to split the header, so if necessary, pad to the end
-- 
2.40.0.348.gf938b09366-goog