Xend will do a hypercall to destory domain when creating VTI guest fail. if "is_vti" 
not be set at this point, HV will call relinquish_vcpu_resource() which belong
to domU. It may try to free a NULL pointer, so dom0 crash. 
This patch fix it.

Signed-off-by, Xu Anthony < Anthony.xu@intel.com >
Signed-off-by, Zhang Xin < xing.z.zhang@intel.com >
diff -r 43115ffc6635 xen/arch/ia64/xen/vhpt.c
--- a/xen/arch/ia64/xen/vhpt.c	Tue Jan 16 12:01:03 2007 -0700
+++ b/xen/arch/ia64/xen/vhpt.c	Fri Jan 19 06:36:31 2007 +0800
@@ -177,7 +177,8 @@ void
 void
 pervcpu_vhpt_free(struct vcpu *v)
 {
-	free_domheap_pages(v->arch.vhpt_page, VHPT_SIZE_LOG2 - PAGE_SHIFT);
+    if ( likely(v->arch.vhpt_page != NULL) )
+        free_domheap_pages(v->arch.vhpt_page, VHPT_SIZE_LOG2 - PAGE_SHIFT);
 }
 #endif