Without it a PVH dom0 is mostly useless, as it would balloon down huge
amounts of RAM in order get physical address space to map foreign
memory and grants, ultimately leading to an out of memory situation.

Such option is also needed for HVM or PVH driver domains, since they
also require mapping grants into physical memory regions.
Suggested-by: NIan Jackson <ian.jackson@eu.citrix.com>
Signed-off-by: NRoger Pau Monné <roger.pau@citrix.com>
Link: https://lore.kernel.org/r/20200324150015.50496-2-roger.pau@citrix.comReviewed-by: NJuergen Gross <jgross@suse.com>
Signed-off-by: NBoris Ostrovsky <boris.ostrovsky@oracle.com>