From 9655f71758003f93294e82926783024a7e4bcdde Mon Sep 17 00:00:00 2001
From: Jonathan Behrens <fintelia@gmail.com>
Date: Mon, 30 Aug 2021 16:27:52 -0400
Subject: [PATCH] Configure PMP at boot

---
 kernel/riscv.h | 12 ++++++++++++
 kernel/start.c |  5 +++++
 2 files changed, 17 insertions(+)

diff --git a/kernel/riscv.h b/kernel/riscv.h
index 0aec003..33b4335 100644
--- a/kernel/riscv.h
+++ b/kernel/riscv.h
@@ -181,6 +181,18 @@ w_mtvec(uint64 x)
   asm volatile("csrw mtvec, %0" : : "r" (x));
 }
 
+static inline void
+w_pmpcfg0(uint64 x)
+{
+  asm volatile("csrw pmpcfg0, %0" : : "r" (x));
+}
+
+static inline void
+w_pmpaddr0(uint64 x)
+{
+  asm volatile("csrw pmpaddr0, %0" : : "r" (x));
+}
+
 // use riscv's sv39 page table scheme.
 #define SATP_SV39 (8L << 60)
 
diff --git a/kernel/start.c b/kernel/start.c
index 1876680..938e837 100644
--- a/kernel/start.c
+++ b/kernel/start.c
@@ -38,6 +38,11 @@ start()
   w_mideleg(0xffff);
   w_sie(r_sie() | SIE_SEIE | SIE_STIE | SIE_SSIE);
 
+  // configure Physical Memory Protection to give supervisor mode
+  // access to all of physical memory.
+  w_pmpaddr0(0x3fffffffffffffull);
+  w_pmpcfg0(0xf);
+
   // ask for clock interrupts.
   timerinit();