From dd1d7e22237203965bf0d8e1f8e5d9b06169e3b1 Mon Sep 17 00:00:00 2001
From: brynet <brynet@openbsd.org>
Date: Tue, 24 Jul 2018 17:31:23 +0000
Subject: [PATCH] Do the same for i386 as amd64:

Add "Mitigation G-2" per AMD's Whitepaper "Software Techniques for
Managing Speculation on AMD Processors"

By setting MSR C001_1029[1]=1, LFENCE becomes a dispatch serializing
instruction.

ok deraadt@
---
 sys/arch/i386/i386/machdep.c       | 22 +++++++++++++++++++++-
 sys/arch/i386/include/specialreg.h |  3 ++-
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/sys/arch/i386/i386/machdep.c b/sys/arch/i386/i386/machdep.c
index 350c7d65ed6..e44bc0fd544 100644
--- a/sys/arch/i386/i386/machdep.c
+++ b/sys/arch/i386/i386/machdep.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: machdep.c,v 1.620 2018/07/10 04:19:59 guenther Exp $	*/
+/*	$OpenBSD: machdep.c,v 1.621 2018/07/24 17:31:23 brynet Exp $	*/
 /*	$NetBSD: machdep.c,v 1.214 1996/11/10 03:16:17 thorpej Exp $	*/
 
 /*-
@@ -2023,6 +2023,26 @@ identifycpu(struct cpu_info *ci)
 		printf("\n");
 	}
 
+	/*
+	 * "Mitigation G-2" per AMD's Whitepaper "Software Techniques
+	 * for Managing Speculation on AMD Processors"
+	 *
+	 * By setting MSR C001_1029[1]=1, LFENCE becomes a dispatch
+	 * serializing instruction.
+	 *
+	 * This MSR is available on all AMD families >= 10h, except 11h
+ 	 * where LFENCE is always serializing.
+	 */
+	if (!strcmp(cpu_vendor, "AuthenticAMD")) {
+		if (ci->ci_family >= 0x10 && ci->ci_family != 0x11) {
+			uint64_t msr;
+
+			msr = rdmsr(MSR_DE_CFG);
+			msr |= DE_CFG_SERIALIZE_LFENCE;
+			wrmsr(MSR_DE_CFG, msr);
+		}
+	}
+
 	/*
 	 * Attempt to disable Silicon Debug and lock the configuration
 	 * if it's enabled and unlocked.
diff --git a/sys/arch/i386/include/specialreg.h b/sys/arch/i386/include/specialreg.h
index 3c5de81b402..ad4668bbb4b 100644
--- a/sys/arch/i386/include/specialreg.h
+++ b/sys/arch/i386/include/specialreg.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: specialreg.h,v 1.66 2018/05/28 20:52:44 bluhm Exp $	*/
+/*	$OpenBSD: specialreg.h,v 1.67 2018/07/24 17:31:23 brynet Exp $	*/
 /*	$NetBSD: specialreg.h,v 1.7 1994/10/27 04:16:26 cgd Exp $	*/
 
 /*-
@@ -484,6 +484,7 @@
 
 #define MSR_DE_CFG	0xc0011029		/* Decode Configuration */
 #define	DE_CFG_721	0x00000001	/* errata 721 */
+#define	DE_CFG_SERIALIZE_LFENCE	(1 << 1)	/* Enable serializing lfence */
 
 #define IPM_C1E_CMP_HLT	0x10000000
 #define IPM_SMI_CMP_HLT	0x08000000
-- 
2.20.1