From 3da443021fdbd2141faf7651fb8433c80d316d7f Mon Sep 17 00:00:00 2001
From: Peter Grehan <grehan@FreeBSD.org>
Date: Thu, 16 Mar 2017 03:21:42 +0000
Subject: [PATCH] Hide the AMD MONITORX/MWAITX capability. Otherwise, recent
 Linux guests will use these instructions, resulting in #UD exceptions since
 bhyve doesn't implement MONITOR/MWAIT exits.

This fixes boot-time hangs in recent Linux guests on Ryzen CPUs
(and probably Bulldozer aka AMD FX as well).

Reviewed by:	kib
MFC after:	1 week
---
 sys/amd64/vmm/x86.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/sys/amd64/vmm/x86.c b/sys/amd64/vmm/x86.c
index 525e1d9b912f..61d99d502ac2 100644
--- a/sys/amd64/vmm/x86.c
+++ b/sys/amd64/vmm/x86.c
@@ -176,6 +176,9 @@ x86_emulate_cpuid(struct vm *vm, int vcpu_id,
 			/* Don't advertise the OS visible workaround feature */
 			regs[2] &= ~AMDID2_OSVW;
 
+			/* Hide mwaitx/monitorx capability from the guest */
+			regs[2] &= ~AMDID2_MWAITX;
+
 			/*
 			 * Hide rdtscp/ia32_tsc_aux until we know how
 			 * to deal with them.