diff -r ba2dc1c221fe xen/arch/x86/hvm/hvm.c
--- a/xen/arch/x86/hvm/hvm.c	Wed Feb 04 16:37:30 2009 +0000
+++ b/xen/arch/x86/hvm/hvm.c	Thu Feb 12 13:43:33 2009 +0000
@@ -541,6 +541,22 @@
                  ctxt.msr_efer);
         return -EINVAL;
     }
+
+    /* Older Xen versions used to save the segment arbytes directly 
+     * from the VMCS on Intel hosts.  Detect this and rearrange them
+     * into the struct segment_register format. */
+#define UNFOLD_ARBYTES(_r)                          \
+    if ( (_r & 0xf000) && !(_r & 0x0f00) )          \
+        _r = ((_r & 0xff) | ((_r >> 4) & 0xf00))
+    UNFOLD_ARBYTES(ctxt.cs_arbytes);
+    UNFOLD_ARBYTES(ctxt.ds_arbytes);
+    UNFOLD_ARBYTES(ctxt.es_arbytes);
+    UNFOLD_ARBYTES(ctxt.fs_arbytes);
+    UNFOLD_ARBYTES(ctxt.gs_arbytes);
+    UNFOLD_ARBYTES(ctxt.ss_arbytes);
+    UNFOLD_ARBYTES(ctxt.tr_arbytes);
+    UNFOLD_ARBYTES(ctxt.ldtr_arbytes);
+#undef UNFOLD_ARBYTES
 
     /* Architecture-specific vmcs/vmcb bits */
     if ( hvm_funcs.load_cpu_ctxt(v, &ctxt) < 0 )