[PATCH net v5 1/2] gve: refuse XDP on queue formats without XDP support

[Amaan Cheval]

Commit d8a8ca14c937 ("gve: add XDP_TX and XDP_REDIRECT support for DQ
RDA") enabled XDP on DQO-RDA by dropping the queue_format check from
verify_xdp_configuration(), which until then refused every format but
GQI-QPL. Nothing replaced it: gve_set_netdev_xdp_features() advertises
no XDP features for DQO-QPL and gve_xdp_xmit() rejects it, but the core
only checks that ndo_bpf exists, so a native XDP program, and an AF_XDP
socket on top of it, can still be attached on a queue format the driver
does not support.

The DQO-QPL RX path was never written for that. Its page accounting
assumes the driver keeps a reference of its own across every handoff:
gve_xdp_done_dqo() passes the buffer to xdp_do_redirect() and then
recycles it with gve_reuse_buffer(), so a redirect target that releases
the buffer synchronously, such as an AF_XDP socket in copy mode, can
drop the page's last reference when pagecnt_bias runs out. The page is
then freed while it is still DMA-mapped and registered in the QPL, and
the driver posts it back to the device.

Refuse XDP setup in gve_verify_xdp_configuration() whenever the driver
advertises no XDP features for the current queue format, which today
means DQO-QPL. A zero-copy XSK pool bind is already refused by the core
for the same reason, and a copy-mode bind never reaches the driver and
is harmless without a program.

Fixes: d8a8ca14c937 ("gve: add XDP_TX and XDP_REDIRECT support for DQ RDA")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Amaan Cheval <amaan.cheval@xxxxxxxxx>
---
v5:
 - Check dev->xdp_features instead of queue_format, and reword the
   subject and message around that (Joshua).
v4: https://lore.kernel.org/netdev/20261106114551.212675-2-amaan.cheval@xxxxxxxxx/

 drivers/net/ethernet/google/gve/gve_main.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
index 2437cd8ba633..fe560f5c5408 100644
--- a/drivers/net/ethernet/google/gve/gve_main.c
+++ b/drivers/net/ethernet/google/gve/gve_main.c
@@ -1723,6 +1723,12 @@ static int gve_verify_xdp_configuration(struct net_device *dev,
 	struct gve_priv *priv = netdev_priv(dev);
 	u16 max_xdp_mtu;
 
+	if (!(dev->xdp_features & NETDEV_XDP_ACT_BASIC)) {
+		NL_SET_ERR_MSG_MOD(extack,
+				   "XDP is not supported on this queue format.");
+		return -EOPNOTSUPP;
+	}
+
 	if (dev->features & NETIF_F_GRO_HW) {
 		NL_SET_ERR_MSG_MOD(extack,
 				   "XDP is not supported when HW-GRO is on.");
-- 
2.47.3