Index: src/sys/uvm/uvm_swap.c
===================================================================
--- src/sys/uvm/uvm_swap.c	23 Aug 2021 13:08:18 -0000	1.206
+++ src/sys/uvm/uvm_swap.c	11 Jul 2022 17:05:56 -0000
@@ -1190,6 +1190,22 @@ again:
  */
 
 /*
+ * swopen: allow the initial open from uvm_swap_init() and reject all others.
+ */
+
+static int
+swopen(dev_t dev, int flag, int mode, struct lwp *l)
+{
+	static bool inited = false;
+
+	if (!inited) {
+		inited = true;
+		return 0;
+	}
+	return ENODEV;
+}
+
+/*
  * swstrategy: perform I/O on the drum
  *
  * => we must map the i/o request from the drum to the correct swapdev.
@@ -1308,8 +1324,8 @@ swwrite(dev_t dev, struct uio *uio, int 
 }
 
 const struct bdevsw swap_bdevsw = {
-	.d_open = nullopen,
-	.d_close = nullclose,
+	.d_open = swopen,
+	.d_close = noclose,
 	.d_strategy = swstrategy,
 	.d_ioctl = noioctl,
 	.d_dump = nodump,