Fedora xen - Mar 2009 - Need help for thesis on Xen - disabling HAP for benchmarking purposes

Hi,

I''m a German student, writing my thesis on "Virtualization with
Xen.
Analysis and Comparision of Different Techniques such as 
Paravirtualization, Full Virtualization, and Utilization of Hardware 
Support Provided by the Processor".

I''d like to know how I can disable HAP/RVI/Nested Paging for 
benchmarking purposes. I read somewhere 
(http://markmail.org/message/bbnivuqx6vjz7jg4) that Xen developers 
decided to disable the global grub parameter introducing a per domain 
flag for HAP instead (hap=0/1).

I used virt-manager built in CentOS for setting up all domUs; 
virt-manager uses libvirt so that no "old-style" configuration files
are
stored in /etc/xen. I actually don''t know how if libvirt-XML-files 
already support something like <hap>0</hap>. How would you proceed 
to
modify an already existing domain using libvirt/virt-manager?

I really do apologize for my "newbie ignorance". Thanks in advance for
any useful help.

- Alex