diff -r 01e178f7ec6d xen/arch/x86/hvm/vmx/realmode.c
--- a/xen/arch/x86/hvm/vmx/realmode.c	Mon Jan 28 12:58:57 2008 +0000
+++ b/xen/arch/x86/hvm/vmx/realmode.c	Wed Jan 30 09:36:29 2008 -0800
@@ -410,6 +410,44 @@ realmode_write_cr(
     return X86EMUL_OKAY;
 }
 
+static int
+realmode_read_msr(
+    unsigned long reg,
+    uint64_t *val,
+    struct x86_emulate_ctxt *ctxt)
+{
+    switch ( reg )
+    {
+    case 0xc0000080L: /* IA32_EFER */
+        rdmsrl(reg, *val);
+        break;
+    default:
+        gdprintk(XENLOG_ERR, "reading of msr 0x%lx by guest not allowed\n", reg);
+        return X86EMUL_UNHANDLEABLE;
+    }
+
+    return X86EMUL_OKAY;
+}
+
+static int
+realmode_write_msr(
+    unsigned long reg,
+    uint64_t val,
+    struct x86_emulate_ctxt *ctxt)
+{
+    switch ( reg )
+    {
+    case 0xc0000080L: /* IA32_EFER */
+        wrmsrl(reg, val);
+        break;
+    default:
+        gdprintk(XENLOG_ERR, "writing of msr 0x%lx by guest not allowed\n", reg);
+        return X86EMUL_UNHANDLEABLE;
+    }
+
+    return X86EMUL_OKAY;
+}
+
 static int realmode_write_rflags(
     unsigned long val,
     struct x86_emulate_ctxt *ctxt)
@@ -495,6 +533,8 @@ static struct x86_emulate_ops realmode_e
     .write_io      = realmode_write_io,
     .read_cr       = realmode_read_cr,
     .write_cr      = realmode_write_cr,
+    .read_msr      = realmode_read_msr,
+    .write_msr     = realmode_write_msr,
     .write_rflags  = realmode_write_rflags,
     .wbinvd        = realmode_wbinvd,
     .cpuid         = realmode_cpuid,