From fc0f08c65112e50a75d77042d8249b6bd15a3b76 Mon Sep 17 00:00:00 2001
From: cinap_lenrek <cinap_lenrek@felloff.net>
Date: Fri, 11 Dec 2020 15:23:03 +0100
Subject: [PATCH] pc, pc64: make sure write combining is supported in MTRR's
 before setting it

---
 sys/src/9/pc/mtrr.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sys/src/9/pc/mtrr.c b/sys/src/9/pc/mtrr.c
index 7601ef543..f840b159d 100644
--- a/sys/src/9/pc/mtrr.c
+++ b/sys/src/9/pc/mtrr.c
@@ -678,6 +678,10 @@ mtrr(uvlong base, uvlong size, char *tstr)
 	if((new.type = str2type(tstr)) < 0)
 		return "bad cache type";
 
+	if(new.type == Writecomb
+	&& (cpu0state.cap & Capwc) == 0)
+		return "write combining not supported";
+
 	qlock(&mtrrlk);
 	newstate = cpu0state;
 	nr = getranges(&newstate, ranges, Nranges, &new);