Fixed by http://xenbits.xensource.com/staging/linux-2.6.18-xen.hg?rev/877c2e42a701 This affects the RHEL5 and RHEL45 kernels.
in 2.6.18-40.el5 You can download this test kernel from http://people.redhat.com/dzickus/el5
An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on the solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHBA-2007-0959.html