Index: xen-4.0.0-testing/xen/arch/x86/hvm/hvm.c
===================================================================
--- xen-4.0.0-testing.orig/xen/arch/x86/hvm/hvm.c
+++ xen-4.0.0-testing/xen/arch/x86/hvm/hvm.c
@@ -629,11 +629,12 @@ static int hvm_load_cpu_ctxt(struct doma
         return -EINVAL;
     }
 
-    if ( (ctxt.msr_efer & ~(EFER_FFXSE | EFER_LME | EFER_LMA |
+    if ( (ctxt.msr_efer & ~(EFER_FFXSE | EFER_LMSLE | EFER_LME | EFER_LMA |
                             EFER_NX | EFER_SCE)) ||
          ((sizeof(long) != 8) && (ctxt.msr_efer & EFER_LME)) ||
          (!cpu_has_nx && (ctxt.msr_efer & EFER_NX)) ||
          (!cpu_has_syscall && (ctxt.msr_efer & EFER_SCE)) ||
+         (!cpu_has_lmsl && (ctxt.msr_efer & EFER_LMSLE)) ||
          (!cpu_has_ffxsr && (ctxt.msr_efer & EFER_FFXSE)) ||
          ((ctxt.msr_efer & (EFER_LME|EFER_LMA)) == EFER_LMA) )
     {
@@ -984,10 +985,11 @@ int hvm_set_efer(uint64_t value)
 
     value &= ~EFER_LMA;
 
-    if ( (value & ~(EFER_FFXSE | EFER_LME | EFER_NX | EFER_SCE)) ||
+    if ( (value & ~(EFER_FFXSE | EFER_LMSLE | EFER_LME | EFER_NX | EFER_SCE)) ||
          ((sizeof(long) != 8) && (value & EFER_LME)) ||
          (!cpu_has_nx && (value & EFER_NX)) ||
          (!cpu_has_syscall && (value & EFER_SCE)) ||
+         (!cpu_has_lmsl && (value & EFER_LMSLE)) ||
          (!cpu_has_ffxsr && (value & EFER_FFXSE)) )
     {
         gdprintk(XENLOG_WARNING, "Trying to set reserved bit in "
Index: xen-4.0.0-testing/xen/arch/x86/hvm/svm/svm.c
===================================================================
--- xen-4.0.0-testing.orig/xen/arch/x86/hvm/svm/svm.c
+++ xen-4.0.0-testing/xen/arch/x86/hvm/svm/svm.c
@@ -56,6 +56,11 @@
 
 u32 svm_feature_flags;
 
+#ifdef __x86_64__
+/* indicate whether guest may use EFER.LMSLE */
+unsigned char cpu_has_lmsl = 0;
+#endif
+
 #define set_segment_register(name, value)  \
     asm volatile ( "movw %%ax ,%%" STR(name) "" : : "a" (value) )
 
@@ -847,6 +852,29 @@ static int svm_cpu_up(struct cpuinfo_x86
     /* Initialize core's ASID handling. */
     svm_asid_init(c);
 
+#ifdef __x86_64__
+    /*
+     * Check whether EFER.LMSLE can be written.
+     * Unfortunately there's no feature bit defined for this.
+     */
+    eax = read_efer();
+    edx = read_efer() >> 32;
+    if ( wrmsr_safe(MSR_EFER, eax | EFER_LMSLE, edx) == 0 )
+        rdmsr(MSR_EFER, eax, edx);
+    if ( eax & EFER_LMSLE )
+    {
+        if ( c == &boot_cpu_data )
+            cpu_has_lmsl = 1;
+        wrmsr(MSR_EFER, eax ^ EFER_LMSLE, edx);
+    }
+    else
+    {
+        if ( cpu_has_lmsl )
+            printk(XENLOG_WARNING "Inconsistent LMLSE support across CPUs!\n");
+        cpu_has_lmsl = 0;
+    }
+#endif
+
     return 1;
 }
 
Index: xen-4.0.0-testing/xen/include/asm-x86/hvm/hvm.h
===================================================================
--- xen-4.0.0-testing.orig/xen/include/asm-x86/hvm/hvm.h
+++ xen-4.0.0-testing/xen/include/asm-x86/hvm/hvm.h
@@ -132,6 +132,12 @@ struct hvm_function_table {
 extern struct hvm_function_table hvm_funcs;
 extern int hvm_enabled;
 
+#ifdef __i386__
+# define cpu_has_lmsl 0
+#else
+extern unsigned char cpu_has_lmsl;
+#endif
+
 int hvm_domain_initialise(struct domain *d);
 void hvm_domain_relinquish_resources(struct domain *d);
 void hvm_domain_destroy(struct domain *d);