diff -r a1fcb77b2ccb xen/arch/x86/hvm/svm/nestedsvm.c
--- a/xen/arch/x86/hvm/svm/nestedsvm.c	Fri Sep 09 10:22:40 2011 +0200
+++ b/xen/arch/x86/hvm/svm/nestedsvm.c	Tue Oct 11 15:56:44 2011 +0200
@@ -51,7 +51,8 @@ nestedsvm_vcpu_stgi(struct vcpu *v)
 static int
 nestedsvm_vmcb_isvalid(struct vcpu *v, uint64_t vmcxaddr)
 {
-    if ( !hvm_svm_enabled(v) || hvm_guest_x86_mode(v) < 2 )
+    /* Address must be 4k aligned */
+    if ( (vmcxaddr & ~PAGE_MASK) != 0 )
         return 0;
 
     /* Maximum valid physical address.