pc: ACPI BIOS: use highest NUMA node for hotplug mem hole SRAT entry

For reasons unknown, Windows won't online all memory, both at command
line and hot-plugged later, unless the hotplug mem hole SRAT entry
specifies a node greater than or equal to the ones where memory is
added.

Using the highest node on the machine makes recent versions of Windows
happy.

With this example command line:
  ... \
  -m 1024,slots=4,maxmem=32G \
  -numa node,nodeid=0 \
  -numa node,nodeid=1 \
  -numa node,nodeid=2 \
  -numa node,nodeid=3 \
  -object memory-backend-ram,size=1G,id=mem-mem1 \
  -device pc-dimm,id=dimm-mem1,memdev=mem-mem1,node=1

Windows reports a total of 1G of RAM without this commit and the expected
2G with this commit.
Signed-off-by: NLadi Prosek <lprosek@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>
Acked-by: NLaszlo Ersek <lersek@redhat.com>

hw/i386/acpi-build.c

@@ -2404,14 +2404,17 @@ build_srat(GArray *table_data, BIOSLinker *linker, MachineState *machine)
     }
 
     /*
-     * Entry is required for Windows to enable memory hotplug in OS.
+     * Entry is required for Windows to enable memory hotplug in OS
+     * and for Linux to enable SWIOTLB when booted with less than
+     * 4G of RAM. Windows works better if the entry sets proximity
+     * to the highest NUMA node in the machine.
      * Memory devices may override proximity set by this entry,
      * providing _PXM method if necessary.
      */
     if (hotplugabble_address_space_size) {
         numamem = acpi_data_push(table_data, sizeof *numamem);
         build_srat_memory(numamem, pcms->hotplug_memory.base,
-                          hotplugabble_address_space_size, 0,
+                          hotplugabble_address_space_size, pcms->numa_nodes - 1,
                           MEM_AFFINITY_HOTPLUGGABLE | MEM_AFFINITY_ENABLED);
     }