libxl/PCI: align reserved device memory boundary for HAP guests

As the code comment says, this will allow use of a 2Mb super page
mapping at the end of "low" memory.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Wei Liu <wl@xen.org>

tools/libxl/libxl_dm.c

@@ -562,6 +562,13 @@ int libxl__domain_device_construct_rdm(libxl__gc *gc,
 
         /* Just check if RDM > our memory boundary. */
         if (rdm_start > rdm_mem_boundary) {
+            /*
+             * For HAP guests round down to a 2Mb boundary to allow use
+             * of large page mappings.
+             */
+            if (libxl_defbool_val(d_config->c_info.hap)
+                && rdm_start > MB(2))
+                rdm_start &= ~(MB(2) - 1);
             /*
              * We will move downwards lowmem_end so we have to expand
              * highmem_end.