git: 17d214c2ca9f - main - bhyve: implement rdmsr for MSR_IA32_FEATURE_CONTROL

[Peter Grehan]

The branch main has been updated by grehan:

URL: https://cgit.FreeBSD.org/src/commit/?id=17d214c2ca9f110db3fa2a10d6b448d624e87774

commit 17d214c2ca9f110db3fa2a10d6b448d624e87774
Author:     Corvin Köhne <C.Koehne at beckhoff.com>
AuthorDate: 2021-04-15 03:49:19 +0000
Commit:     Peter Grehan <grehan at FreeBSD.org>
CommitDate: 2021-04-15 03:49:19 +0000

    bhyve: implement rdmsr for MSR_IA32_FEATURE_CONTROL
    
    Without the -w option, Windows guests crash on boot. This is caused by a rdmsr
    of MSR_IA32_FEATURE_CONTROL. Windows checks this MSR to determine enabled VMX
    features. This MSR isn't emulated in bhyve, so a #GP exception is injected
    which causes Windows to crash.
    
    Fix by returning a rdmsr of MSR_IA32_FEATURE_CONTROL with Lock Bit set and
    VMX disabled to informWindows that VMX isn't available.
    
    Reviewed by:    jhb, grehan (bhyve)
    MFC after:      1 week
    Differential Revision:  https://reviews.freebsd.org/D29665
---
 usr.sbin/bhyve/xmsr.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/usr.sbin/bhyve/xmsr.c b/usr.sbin/bhyve/xmsr.c
index 0b87821836b7..1a7f98ee222a 100644
--- a/usr.sbin/bhyve/xmsr.c
+++ b/usr.sbin/bhyve/xmsr.c
@@ -124,6 +124,14 @@ emulate_rdmsr(struct vmctx *ctx, int vcpu, uint32_t num, uint64_t *val)
 			 */
 			*val = 0x000a1003;
 			break;
+		case MSR_IA32_FEATURE_CONTROL:
+			/*
+			 * Windows guests check this MSR.
+			 * Set the lock bit to avoid writes
+			 * to this MSR.
+			 */
+			*val = IA32_FEATURE_CONTROL_LOCK;
+			break;
 		default:
 			error = -1;
 			break;