diff --git a/sys/riscv/riscv/pmap.c b/sys/riscv/riscv/pmap.c
--- a/sys/riscv/riscv/pmap.c
+++ b/sys/riscv/riscv/pmap.c
@@ -3146,6 +3146,24 @@
 	    PMAP_ENTER_NOREPLACE | PMAP_ENTER_NORECLAIM, NULL, lockp));
 }
 
+/*
+ * Returns true if every page table entry in the specified page table is
+ * zero.
+ */
+static bool
+pmap_every_pte_zero(vm_paddr_t pa)
+{
+	pt_entry_t *pt_end, *pte;
+
+	KASSERT((pa & PAGE_MASK) == 0, ("pa is misaligned"));
+	pte = (pt_entry_t *)PHYS_TO_DMAP(pa);
+	for (pt_end = pte + Ln_ENTRIES; pte < pt_end; pte++) {
+		if (*pte != 0)
+			return (false);
+	}
+	return (true);
+}
+
 /*
  * Tries to create the specified 2MB page mapping.  Returns KERN_SUCCESS if
  * the mapping was created, and one of KERN_FAILURE, KERN_NO_SPACE, or
@@ -3191,7 +3209,8 @@
 				    "pmap_enter_l2: no space for va %#lx"
 				    " in pmap %p", va, pmap);
 				return (KERN_NO_SPACE);
-			} else {
+			} else if (va < VM_MAXUSER_ADDRESS ||
+			    !pmap_every_pte_zero(L2PTE_TO_PHYS(oldl2))) {
 				CTR2(KTR_PMAP, "pmap_enter_l2:"
 				    " failed to replace existing mapping"
 				    " for va %#lx in pmap %p", va, pmap);