1GB Page Table Support for HVM Guest

Keir,

Could you apply this patch set to Xen tree? These patches are sync-ed with Xen tree.

These three patches enable 1GB host page table support for HVM guests running under HAP mode. They are similar to patches submitted several days ago, but with fixes based on the comments from Tim and Keir. We provide an option ("hap_1gb") to turn this feature on/off. The patches have been tested on AMD and Intel platforms (live migration, domain save and restore, etc.).

Thanks,
-Wei