Xen devel - Nov 2011 - xenloop alloc_vm_area crashes domU

I am trying to port Xenloop to Xen 4.0.1 and 2.6.35. It uses the
following piece of code to map a granted page:

	xfc->descriptor_vmarea = alloc_vm_area(PAGE_SIZE);
	xfc->fifo_vmarea = alloc_vm_area( MAX_FIFO_PAGES*PAGE_SIZE );
	if(!xfc->descriptor_vmarea || !xfc->fifo_vmarea) {
		EPRINTK("error: cannot allocate memory for descriptor OR FIFO\n");
		goto err;
	}

	gnttab_set_map_op(&map_op, (unsigned
long)xfc->descriptor_vmarea->addr,
				GNTMAP_host_map, remote_gref, remote_domid);
	ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &map_op, 1);

but alloc_vm_area fails and crashes domU. in_interrupt() returns 256
and I think this is the cause. Any idea about what should I do?
Thanks,
- Mohammad