From ed101befeefe470e49bec32b9f4efd600bdbda46 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Wed, 24 Aug 2022 13:47:47 -0400
Subject: [PATCH] comment the sfences
---
kernel/trampoline.S | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
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