[PATCH net 4/6] gve: don't register xsk pool on pre-existing queues in RDA mode

[Joshua Washington <joshwash@google.com>]

When XSK pools are enabled after an XDP program has already been loaded,
XSK pools are registered on pre-existing queues before queues are
re-created with the XSK pool fully registered in DQ RDA mode.

This can lead to a race condition between the RX NAPI and the control
plane thread wherein a pre-existing queue sees the live XSK pool and
attempts to use recycled buffers not backed by XSK buffs for AF_XDP ZC
traffic. This causes the following kernel panic to occur when attempting
to DMA map a NULL XSK buffer:

BUG: kernel NULL pointer dereference, address: 0000000000000050
...
RIP: 0010:gve_rx_post_buffers_dqo+0x99/0x190 [gve]
...
Call Trace:
 <TASK>
 gve_rx_poll_dqo+0x4d9/0xf10 [gve]
 gve_napi_poll_dqo+0x76/0x170 [gve]
 __napi_poll+0x28/0x160
 net_rx_action+0x2a0/0x350
 handle_softirqs+0xd4/0x280
 ? sort_range+0x20/0x20
 run_ksoftirqd+0x2d/0x40
 smpboot_thread_fn+0xd5/0x1d0
 kthread+0xd7/0x100
 ? kthread_complete_and_exit+0x20/0x20
 ret_from_fork+0x1f/0x30
 </TASK>

The XSK pool should only be registered with current queues if XSK
buffers are allocated on-the-fly, as is the case in QPL mode.

Fixes: c1fffc5d66a7 ("gve: implement DQO RX datapath and control path for AF_XDP zero-copy")
Cc: stable@vger.kernel.org
Reviewed-by: Jordan Rhee <jordanrhee@google.com>
Reviewed-by: Tim Hostetler <thostet@google.com>
Signed-off-by: Joshua Washington <joshwash@google.com>
---
 drivers/net/ethernet/google/gve/gve_main.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
index e4d78ae52daf..453b304016b6 100644
--- a/drivers/net/ethernet/google/gve/gve_main.c
+++ b/drivers/net/ethernet/google/gve/gve_main.c
@@ -1654,20 +1654,18 @@ static int gve_xsk_pool_enable(struct net_device *dev,
 	if (!priv->xdp_prog || !netif_running(dev))
 		return 0;
 
-	err = gve_reg_xsk_pool(priv, dev, pool, qid);
-	if (err)
-		goto err_xsk_pool_dma_mapped;
-
-	/* Stop and start RDA queues to repost buffers. */
-	if (!gve_is_qpl(priv)) {
+	if (gve_is_qpl(priv)) {
+		err = gve_reg_xsk_pool(priv, dev, pool, qid);
+		if (err)
+			goto err_xsk_pool_dma_mapped;
+	} else {
+		/* Stop and start RDA queues to repost buffers. */
 		err = gve_configure_rings_xdp(priv, priv->rx_cfg.num_queues);
 		if (err)
-			goto err_xsk_pool_registered;
+			goto err_xsk_pool_dma_mapped;
 	}
 	return 0;
 
-err_xsk_pool_registered:
-	gve_unreg_xsk_pool(priv, qid);
 err_xsk_pool_dma_mapped:
 	clear_bit(qid, priv->xsk_pools);
 	xsk_pool_dma_unmap(pool,
-- 
2.55.0.691.gc56d675ccc-goog