[PATCH net v2] gve: DQO: accept TSO packets with non-protocol gso_type bits

[PATCH net v2] gve: DQO: accept TSO packets with non-protocol gso_type bits

[Hannu Varjoranta]

Since commit 014c607f86ab ("gve: add support for UDP GSO for DQO
format"), gve_prep_tso() matches shinfo->gso_type exactly. gso_type is
a bitmask, though: SKB_GSO_DODGY is set on every GSO packet that comes
from tun/tap, packet sockets or other untrusted sources, and
SKB_GSO_TCP_ECN and SKB_GSO_TCP_FIXEDID can be set as well. Such packets
hit the default case, gve_tx_add_skb_dqo() fails and gve_try_tx_skb()
drops them, counting them in tx_dropped.

These packets do reach the driver: tcp_gso_segment() passes DODGY skbs
through unsegmented to devices that support TSO, after recomputing
gso_segs, so drivers must tolerate the bit.

This breaks virtual machines behind a tap on GCE instances using the DQO
queue formats. Every TSO packet forwarded from a guest (gso_type
SKB_GSO_TCPV4 | SKB_GSO_DODGY) is dropped, and guest uploads slow to a
crawl of retransmissions or stall entirely, while the host's own TSO
traffic (gso_type SKB_GSO_TCPV4) is unaffected. On an n4 instance
(DQO-QPL) with a Cloud Hypervisor guest, a 64 MB upload from the guest
went from a 60 s timeout at ~0.9 MB/s to 0.19 s with this change, with
tx_dropped no longer increasing.

Host TCP with ECN is hit as well: gve advertises NETIF_F_TSO_ECN, so a
TSO packet carrying CWR has SKB_GSO_TCP_ECN set and is dropped too.

Restore the bitmask test that commit 1b9f75634441 ("gve: ignore
nonrelevant GSO type bits when processing TSO headers") introduced for
the same problem, keeping the UDP GSO support.

While here, reload shinfo after skb_cow_head(). If the head was cloned,
pskb_expand_head() moves skb_shared_info to the new head, and the
pointer cached at function entry can then refer to memory that another
clone frees.

Fixes: 014c607f86ab ("gve: add support for UDP GSO for DQO format")
Signed-off-by: Hannu Varjoranta <hannu@varjosoft.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Ankit Garg <nktgrg@google.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
---
v2:
- Reload shinfo after skb_cow_head() (Eric Dumazet, Sashiko review)
- Mention host TCP with ECN in the changelog (Eric Dumazet)
- Rebase on net, on top of commits 83769c23fb18, 3b430ea62340 and
  296c83b5ccc8 (gve_can_send_tso() header length, MSS range checks)
- Carry Reviewed-by tags from v1

v1: https://lore.kernel.org/netdev/20260923141047.14047-1-hannu@varjosoft.com/

 drivers/net/ethernet/google/gve/gve_tx_dqo.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve_tx_dqo.c b/drivers/net/ethernet/google/gve/gve_tx_dqo.c
index 616c1921a..ad99cbb77 100644
--- a/drivers/net/ethernet/google/gve/gve_tx_dqo.c
+++ b/drivers/net/ethernet/google/gve/gve_tx_dqo.c
@@ -595,25 +595,25 @@ static int gve_prep_tso(struct sk_buff *skb)
 	err = skb_cow_head(skb, 0);
 	if (err < 0)
 		return err;
+	shinfo = skb_shinfo(skb);
 
 	l4_start = skb_transport_offset(skb);
 	paylen = skb->len - l4_start;
 
-	switch (shinfo->gso_type) {
-	case SKB_GSO_TCPV4:
-	case SKB_GSO_TCPV6:
+	/* gso_type is a bitmask: SKB_GSO_DODGY, SKB_GSO_TCP_ECN and
+	 * SKB_GSO_TCP_FIXEDID may be set alongside the protocol bit.
+	 */
+	if (shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)) {
 		tcp = tcp_hdr(skb);
 		csum_replace_by_diff(&tcp->check,
 				     (__force __wsum)htonl(paylen));
 		header_len = skb_tcp_all_headers(skb);
-		break;
-	case SKB_GSO_UDP_L4:
+	} else if (shinfo->gso_type & SKB_GSO_UDP_L4) {
 		udp = udp_hdr(skb);
 		csum_replace_by_diff(&udp->check,
 				     (__force __wsum)htonl(paylen));
 		header_len = sizeof(struct udphdr) + l4_start;
-		break;
-	default:
+	} else {
 		return -EINVAL;
 	}
 

base-commit: 11536ee3d3e0b1bd35b6f3f8df55a6053eb0c71d
-- 
2.54.0 (Apple Git-157)

Re: [PATCH net v2] gve: DQO: accept TSO packets with non-protocol gso_type bits

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Fri, 25 Sep 2026 14:52:37 +0300 you wrote:
> Since commit 014c607f86ab ("gve: add support for UDP GSO for DQO
> format"), gve_prep_tso() matches shinfo->gso_type exactly. gso_type is
> a bitmask, though: SKB_GSO_DODGY is set on every GSO packet that comes
> from tun/tap, packet sockets or other untrusted sources, and
> SKB_GSO_TCP_ECN and SKB_GSO_TCP_FIXEDID can be set as well. Such packets
> hit the default case, gve_tx_add_skb_dqo() fails and gve_try_tx_skb()
> drops them, counting them in tx_dropped.
> 
> [...]

Here is the summary with links:
  - [net,v2] gve: DQO: accept TSO packets with non-protocol gso_type bits
    https://git.kernel.org/netdev/net/c/f8932b2c0c9a

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html