machine: introduce convenience MachineState::ram

the new field will be used by boards to get access to main
RAM memory region and will help to save boiler plate in
boards which often introduce a field or variable just for
this purpose.

Memory region will be equivalent to what currently used
memory_region_allocate_system_memory() is returning apart
from that it will come from hostmem backend.
Followup patches will incrementally switch boards to using
RAM from MachineState::ram.

Patch takes care of non-NUMA case and follow up patch will
initialize MachineState::ram for NUMA case.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200219160953.13771-5-imammedo@redhat.com>

hw/core/machine.c

@@ -26,6 +26,7 @@
 #include "sysemu/qtest.h"
 #include "hw/pci/pci.h"
 #include "hw/mem/nvdimm.h"
+#include "migration/vmstate.h"
 
 GlobalProperty hw_compat_4_2[] = {
     { "virtio-blk-device", "x-enable-wce-if-config-wce", "off" },
@@ -1059,10 +1060,33 @@ static void machine_numa_finish_cpu_init(MachineState *machine)
     g_string_free(s, true);
 }
 
+MemoryRegion *machine_consume_memdev(MachineState *machine,
+                                     HostMemoryBackend *backend)
+{
+    MemoryRegion *ret = host_memory_backend_get_memory(backend);
+
+    if (memory_region_is_mapped(ret)) {
+        char *path = object_get_canonical_path_component(OBJECT(backend));
+        error_report("memory backend %s can't be used multiple times.", path);
+        g_free(path);
+        exit(EXIT_FAILURE);
+    }
+    host_memory_backend_set_mapped(backend, true);
+    vmstate_register_ram_global(ret);
+    return ret;
+}
+
 void machine_run_board_init(MachineState *machine)
 {
     MachineClass *machine_class = MACHINE_GET_CLASS(machine);
 
+    if (machine->ram_memdev_id) {
+        Object *o;
+        o = object_resolve_path_type(machine->ram_memdev_id,
+                                     TYPE_MEMORY_BACKEND, NULL);
+        machine->ram = machine_consume_memdev(machine, MEMORY_BACKEND(o));
+    }
+
     if (machine->numa_state) {
         numa_complete_configuration(machine);
         if (machine->numa_state->num_nodes) {

hw/core/numa.c

@@ -817,20 +817,8 @@ void memory_region_allocate_system_memory(MemoryRegion *mr, Object *owner,
         if (!backend) {
             continue;
         }
-        MemoryRegion *seg = host_memory_backend_get_memory(backend);
+        MemoryRegion *seg = machine_consume_memdev(ms, backend);
-
-        if (memory_region_is_mapped(seg)) {
-            char *path = object_get_canonical_path_component(OBJECT(backend));
-            error_report("memory backend %s is used multiple times. Each "
-                         "-numa option must use a different memdev value.",
-                         path);
-            g_free(path);
-            exit(1);
-        }
-
-        host_memory_backend_set_mapped(backend, true);
         memory_region_add_subregion(mr, addr, seg);
-        vmstate_register_ram_global(seg);
         addr += size;
     }
 }

include/hw/boards.h

@@ -73,7 +73,12 @@ void machine_set_cpu_numa_node(MachineState *machine,
                                Error **errp);
 
 void machine_class_allow_dynamic_sysbus_dev(MachineClass *mc, const char *type);
-
+/*
+ * Checks that backend isn't used, preps it for exclusive usage and
+ * returns migratable MemoryRegion provided by backend.
+ */
+MemoryRegion *machine_consume_memdev(MachineState *machine,
+                                     HostMemoryBackend *backend);
 
 /**
  * CPUArchId:
@@ -295,6 +300,11 @@ struct MachineState {
     bool enable_graphics;
     char *memory_encryption;
     char *ram_memdev_id;
+    /*
+     * convenience alias to ram_memdev_id backend memory region
+     * or to numa container memory region
+     */
+    MemoryRegion *ram;
     DeviceMemoryState *device_memory;
 
     ram_addr_t ram_size;