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Date: Thu, 10 Dec 2020 00:18:21 +0100
From: cinap_lenrek@felloff.net
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Subject: Re: [9front] kernel crash in bhyve
Reply-To: 9front@9front.org
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The following diff should fix it.

--
cinap

diff -r dcd57f411618 sys/src/9/pc/memory.c
--- a/sys/src/9/pc/memory.c	Wed Dec 09 01:05:14 2020 +0100
+++ b/sys/src/9/pc/memory.c	Thu Dec 10 00:16:49 2020 +0100
@@ -383,8 +383,16 @@
 		}
 	}
 
-	/* RAM needs to be writeback */
-	mtrrexclude(MemRAM, "wb");
+	/*
+	 * Make sure RAM is set to writeback,
+	 * but do a sanity check first checking
+	 * that the kernel text is writeback.
+	 * This is needed as some emulators (bhyve)
+	 * set everything to uncached.
+	 */
+	s = mtrrattr(KTZERO, nil);
+	if(s != nil && strcmp(s, "wb") == 0)
+		mtrrexclude(MemRAM, "wb");
 
 	for(base = memmapnext(-1, MemRAM); base != -1; base = memmapnext(base, MemRAM)){
 		size = memmapsize(base, BY2PG) & ~(BY2PG-1);