On AMD CPUs, If the LFENCE serialization MSR bit is already set, then

we don't need to uncondtionally set it.

Worksaround a suspected bug in newer Linux KVM, which may trigger a
#GP fault on writes to this MSR.

ok mlarkin@

diff --git a/sys/arch/amd64/amd64/identcpu.c b/sys/arch/amd64/amd64/identcpu.c
index 6e0aee2..4947ce0 100644 (file)
--- a/sys/arch/amd64/amd64/identcpu.c
+++ b/sys/arch/amd64/amd64/identcpu.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: identcpu.c,v 1.103 2018/07/23 23:25:02 brynet Exp $   */
+/*     $OpenBSD: identcpu.c,v 1.104 2018/08/01 20:33:53 brynet Exp $   */
 /*     $NetBSD: identcpu.c,v 1.1 2003/04/26 18:39:28 fvdl Exp $        */
 
 /*
@@ -656,8 +656,10 @@ identifycpu(struct cpu_info *ci)
                        uint64_t msr;
 
                        msr = rdmsr(MSR_DE_CFG);
-                       msr |= DE_CFG_SERIALIZE_LFENCE;
-                       wrmsr(MSR_DE_CFG, msr);
+                       if ((msr & DE_CFG_SERIALIZE_LFENCE) == 0) {
+                               msr |= DE_CFG_SERIALIZE_LFENCE;
+                               wrmsr(MSR_DE_CFG, msr);
+                       }
                }
        }
 

diff --git a/sys/arch/i386/i386/machdep.c b/sys/arch/i386/i386/machdep.c
index a47f5e7..cf18a1e 100644 (file)
--- a/sys/arch/i386/i386/machdep.c
+++ b/sys/arch/i386/i386/machdep.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: machdep.c,v 1.622 2018/07/30 14:19:12 kettenis Exp $  */
+/*     $OpenBSD: machdep.c,v 1.623 2018/08/01 20:33:53 brynet Exp $    */
 /*     $NetBSD: machdep.c,v 1.214 1996/11/10 03:16:17 thorpej Exp $    */
 
 /*-
@@ -2038,8 +2038,10 @@ identifycpu(struct cpu_info *ci)
                        uint64_t msr;
 
                        msr = rdmsr(MSR_DE_CFG);
-                       msr |= DE_CFG_SERIALIZE_LFENCE;
-                       wrmsr(MSR_DE_CFG, msr);
+                       if ((msr & DE_CFG_SERIALIZE_LFENCE) == 0) {
+                               msr |= DE_CFG_SERIALIZE_LFENCE;
+                               wrmsr(MSR_DE_CFG, msr);
+                       }
                }
        }