diff --git a/kernel/trampoline.S b/kernel/trampoline.S
index 7fb0b36..d7308cc 100644
--- a/kernel/trampoline.S
+++ b/kernel/trampoline.S
@@ -80,10 +80,18 @@ uservec:
         # load the address of usertrap(), from p->trapframe->kernel_trap
         ld t0, 16(a0)
 
-        # load the kernel page table, from p->trapframe->kernel_satp
+
+        # fetch the kernel page table address, from p->trapframe->kernel_satp.
         ld t1, 0(a0)
+
+        # wait for any previous memory operations to complete, so that
+        # they use the user page table.
         sfence.vma zero, zero
+
+        # install the kernel page table.
         csrw satp, t1
+
+        # flush now-stale user entries from the TLB.
         sfence.vma zero, zero
 
         # jump to usertrap(), which does not return