[PATCH net 1/2] gve: fix TX drop when GSO MSS is too small for hw

From: Eddie Phillips <redacted>

The device has a strict requirement that the minimum MSS
(gso_size) for TSO/GSO packets must be at least 88 bytes. If a packet
below this threshold is pushed to the hardware, it can cause
hardware to silently drop the packet, leading to increased latency
and retransmissions.

Currently, this is validated too late in the transmit pipeline
(gve_prep_tso), leading to silent drops.

Fix this by moving the validation into the .ndo_features_check
callback (gve_features_check_dqo). If we detect a GSO packet with
a gso_size smaller than GVE_TX_MIN_TSO_MSS_DQO, we clear the GSO
feature flags for this packet.

Fixes: a57e5de476be ("gve: DQO: Add TX path")
Signed-off-by: Eddie Phillips <redacted>
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 drivers/net/ethernet/google/gve/gve_tx_dqo.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve_tx_dqo.c b/drivers/net/ethernet/google/gve/gve_tx_dqo.c
index 80ab0a449ff54e3d19e9c69226949465d48dfe3f..19829b8e13de28df81bdec0c86e8356b25fe9537 100644
--- a/drivers/net/ethernet/google/gve/gve_tx_dqo.c
+++ b/drivers/net/ethernet/google/gve/gve_tx_dqo.c

@@ -577,17 +577,6 @@ static int gve_prep_tso(struct sk_buff *skb)
 	int header_len;
 	int err;
 
-	/* Note: HW requires MSS (gso_size) to be <= 9728 and the total length
-	 * of the TSO to be <= 262143.
-	 *
-	 * However, we don't validate these because:
-	 * - Hypervisor enforces a limit of 9K MTU
-	 * - Kernel will not produce a TSO larger than 64k
-	 */
-
-	if (unlikely(shinfo->gso_size < GVE_TX_MIN_TSO_MSS_DQO))
-		return -1;
-
 	/* Needed because we will modify header. */
 	err = skb_cow_head(skb, 0);
 	if (err < 0)

@@ -925,6 +914,9 @@ static bool gve_can_send_tso(const struct sk_buff *skb)
 	int cur_seg_size;
 	int i;
 
+	if (unlikely(gso_size < GVE_TX_MIN_TSO_MSS_DQO))
+		return false;
+
 	cur_seg_size = skb_headlen(skb) - header_len;
 	prev_frag_size = skb_headlen(skb);
 	cur_seg_num_bufs = cur_seg_size > 0;

-- 
2.56.0.rc1.310.g51773c2048-goog