xen: add the direct mapping area for ISA bus access

add the direct mapping area for ISA bus access when running as initial
domain

Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index c413132702f7..62ceb7864017 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -119,6 +119,9 @@ char * __init xen_memory_setup(void)
          * Even though this is normal, usable memory under Xen, reserve
          * ISA memory anyway because too many things think they can poke
          * about in there.
+         *
+         * In a dom0 kernel, this region is identity mapped with the
+         * hardware ISA area, so it really is out of bounds.
          */
         e820_add_region(ISA_START_ADDRESS, ISA_END_ADDRESS - ISA_START_ADDRESS,
                         E820_RESERVED);