[PATCH net v4 1/2] gve: block XDP on the DQO-QPL queue format

[Amaan Cheval <amaan.cheval@gmail.com>]

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 for DQO-QPL: gve_set_netdev_xdp_features()
advertises no XDP features there 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 DQO-QPL.

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 program setup on DQO-QPL in gve_verify_xdp_configuration(),
matching the features the driver advertises. 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@vger.kernel.org
Signed-off-by: Amaan Cheval <amaan.cheval@gmail.com>
---
 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..4e9e692a0ed0 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 (priv->queue_format == GVE_DQO_QPL_FORMAT) {
+		NL_SET_ERR_MSG_MOD(extack,
+				   "XDP is not supported in DQO QPL 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