gve: fix the wrong AdminQ buffer overflow check

The 'tail' pointer is also free-running count, so it needs to be masked
as 'adminq_prod_cnt' does, to become an index value of AdminQ buffer.

Fixes: 5cdad90d ("gve: Batch AQ commands for creating and destroying queues.")
Signed-off-by: NHaiyue Wang <haiyue.wang@intel.com>
Reviewed-by: NCatherine Sullivan <csully@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/google/gve/gve_adminq.c

@@ -322,7 +322,8 @@ static int gve_adminq_issue_cmd(struct gve_priv *priv,
 	tail = ioread32be(&priv->reg_bar0->adminq_event_counter);
 
 	// Check if next command will overflow the buffer.
-	if (((priv->adminq_prod_cnt + 1) & priv->adminq_mask) == tail) {
+	if (((priv->adminq_prod_cnt + 1) & priv->adminq_mask) ==
+	    (tail & priv->adminq_mask)) {
 		int err;
 
 		// Flush existing commands to make room.
@@ -332,7 +333,8 @@ static int gve_adminq_issue_cmd(struct gve_priv *priv,
 
 		// Retry.
 		tail = ioread32be(&priv->reg_bar0->adminq_event_counter);
-		if (((priv->adminq_prod_cnt + 1) & priv->adminq_mask) == tail) {
+		if (((priv->adminq_prod_cnt + 1) & priv->adminq_mask) ==
+		    (tail & priv->adminq_mask)) {
 			// This should never happen. We just flushed the
 			// command queue so there should be enough space.
 			return -ENOMEM;