grant table issue

[Xin Zhao <zhaoxin@eecs.umich.edu>]

Hi,

I am trying to export a memory page of dom0 to a domU in readonly mode. 
In dom0, I grant access permission to that domU. In domU, I did
 HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map, res->nr_pages);

All these functions returned successfully. But when I tried to access 
data in the mapped memory page, all data I got is 0. 

Is there any restriction that preventing dom0 pages from being export to 
other domains? If so, is there any way to relax this restriction?

xin