This bug has been copied from bug #723755 and has been proposed to be backported to 5.7 z-stream (EUS).
in kernel-2.6.18-274.4.1.el5 xen-hvm-support-more-opcodes-for-mmio.patch
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. http://rhn.redhat.com/errata/RHSA-2011-1386.html
Technical note added. If any revisions are required, please edit the "Technical Notes" field accordingly. All revisions will be proofread by the Engineering Content Services team. New Contents: Prior to this update, Xen did not implement certain ALU opcodes. As a result, when a driver used the missing opcodes on memory-mapped I/O areas, it caused the guest to crash. This update adds all the missing opcodes. In particular, this fixes a BSOD crash from the Windows e1000 driver.