This bug has been copied from bug #633028 and has been proposed to be backported to 5.5 z-stream (EUS).
in kernel 2.6.18-194.21.1.el5 xen-hvm-correct-accuracy-of-pmtimer.patch
I've tested the reproducer in the tracked bug. Issue reproduced on all the 3 guests - RHEL4, RHEL5, RHEL6 HVM with the specific kernels. I performed the test on kernel-xen-2.6.18-194.15.1.el5, selecting the PM timer in the guest, then running the constantly gettimeofday() code. At the beginning, I confirmed that the time difference between host and guest is no more than 2 seconds, simply using the date command. After running the program about 10 minutes, the difference has increased to about 50 to 60 seconds. Then I updated the kernel-xen package to kernel-xen-2.6.18-194.24.1.el5 from the errata link, rebooted the host and performed the test again. This time the time difference between host and guest has no noticeable change after running the program in the guest for more than 20 minutes. I also did this test on the 3 different guests simultaneously. Again the time drift issue does not occur on the new hypervisor, no matter how long the program runs. As a result I believe this bug could be put into VERIFIED.
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 therefore 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/RHSA-2010-0839.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: A Red Hat Enterprise Linux 4, 5, and 6 Xen HVM guest that uses PM timer for time keeping had the time drift backwards about 5 seconds per minute. This was caused by small inaccuracies in truncating in the pmt_update_time() function. With this update, time is kept accurately and no longer drifts backwards.