I've configured xen 4.6.0 with xsm enabled and use the
default flask policy to boot the dom0.
For issues like this, please always use the latest stable branch, in
this case making that Xen 4.6.1+. It is entirely possible that
bugfixes have been backported.
In this case, can you try current master (or 4.7.0-rc2)? Some of
these errors have definitely been fixed in the 4.7 dev period.