diff --git a/nova/tests/unit/virt/libvirt/fake_libvirt_utils.py b/nova/tests/unit/virt/libvirt/fake_libvirt_utils.py
index 3e1ea8083f7b..7dbc14c2d144 100644
--- a/nova/tests/unit/virt/libvirt/fake_libvirt_utils.py
+++ b/nova/tests/unit/virt/libvirt/fake_libvirt_utils.py
@@ -179,6 +179,10 @@ def cpu_features_to_traits(features):
     return libvirt_utils.cpu_features_to_traits(features)
 
 
+def get_default_machine_type(arch):
+    return libvirt_utils.get_default_machine_type(arch)
+
+
 def mdev_name2uuid(mdev_name):
     return libvirt_utils.mdev_name2uuid(mdev_name)
 
diff --git a/nova/tests/unit/virt/libvirt/test_utils.py b/nova/tests/unit/virt/libvirt/test_utils.py
index 8aeb4af2e074..674b66f0cbc1 100644
--- a/nova/tests/unit/virt/libvirt/test_utils.py
+++ b/nova/tests/unit/virt/libvirt/test_utils.py
@@ -32,6 +32,7 @@ from nova import objects
 from nova.objects import fields as obj_fields
 import nova.privsep.fs
 from nova import test
+from nova.tests import fixtures as nova_fixtures
 from nova.tests.unit import fake_instance
 from nova.tests.unit.virt.libvirt import fakelibvirt
 from nova.virt.disk import api as disk
@@ -969,3 +970,29 @@ sunrpc /var/lib/nfs/rpc_pipefs rpc_pipefs rw,relatime 0 0
         disk_path, format = libvirt_utils.find_disk(guest)
         self.assertEqual('/test/disk', disk_path)
         self.assertEqual('ploop', format)
+
+    def test_machine_type_mappings(self):
+        self.useFixture(nova_fixtures.ConfPatcher(
+            group="libvirt", hw_machine_type=['x86_64=q35', 'i686=legacy']))
+        self.assertDictEqual({'x86_64': 'q35', 'i686': 'legacy'},
+                             libvirt_utils.machine_type_mappings())
+
+    def test_invalid_machine_type_mappings(self):
+        self.useFixture(nova_fixtures.ConfPatcher(
+            group="libvirt", hw_machine_type=['x86_64=q35', 'foo']))
+        self.assertDictEqual({'x86_64': 'q35'},
+                             libvirt_utils.machine_type_mappings())
+
+    def test_get_default_machine_type(self):
+        self.useFixture(nova_fixtures.ConfPatcher(
+            group="libvirt", hw_machine_type=['x86_64=q35', 'i686=legacy']))
+        self.assertEqual('q35',
+                         libvirt_utils.get_default_machine_type('x86_64'))
+
+    def test_get_default_machine_type_empty(self):
+        self.assertIsNone(libvirt_utils.get_default_machine_type('sparc'))
+
+    def test_get_default_machine_type_missing(self):
+        self.useFixture(nova_fixtures.ConfPatcher(
+            group="libvirt", hw_machine_type=['x86_64=q35', 'i686=legacy']))
+        self.assertIsNone(libvirt_utils.get_default_machine_type('sparc'))
diff --git a/nova/virt/libvirt/driver.py b/nova/virt/libvirt/driver.py
index a23b56362427..608ac874296c 100644
--- a/nova/virt/libvirt/driver.py
+++ b/nova/virt/libvirt/driver.py
@@ -4227,13 +4227,6 @@ class LibvirtDriver(driver.ComputeDriver):
 
         return meta
 
-    def _machine_type_mappings(self):
-        mappings = {}
-        for mapping in CONF.libvirt.hw_machine_type:
-            host_arch, _, machine_type = mapping.partition('=')
-            mappings[host_arch] = machine_type
-        return mappings
-
     def _get_machine_type(self, image_meta, caps):
         # The guest machine type can be set as an image metadata
         # property, or otherwise based on architecture-specific
@@ -4257,9 +4250,10 @@ class LibvirtDriver(driver.ComputeDriver):
                 mach_type = 's390-ccw-virtio'
 
             # If set in the config, use that as the default.
-            if CONF.libvirt.hw_machine_type:
-                mappings = self._machine_type_mappings()
-                mach_type = mappings.get(caps.host.cpu.arch)
+            mach_type = (
+                libvirt_utils.get_default_machine_type(caps.host.cpu.arch)
+                or mach_type
+            )
 
         return mach_type
 
diff --git a/nova/virt/libvirt/utils.py b/nova/virt/libvirt/utils.py
index 59bb982caee6..10759f136a7f 100644
--- a/nova/virt/libvirt/utils.py
+++ b/nova/virt/libvirt/utils.py
@@ -541,6 +541,21 @@ def get_cpu_model_from_arch(arch):
     return mode
 
 
+def machine_type_mappings():
+    mappings = {}
+    for mapping in CONF.libvirt.hw_machine_type or {}:
+        host_arch, _, machine_type = mapping.partition('=')
+        if machine_type == '':
+            LOG.warning("Invalid hw_machine_type config value %s", mapping)
+        else:
+            mappings[host_arch] = machine_type
+    return mappings
+
+
+def get_default_machine_type(arch):
+    return machine_type_mappings().get(arch)
+
+
 def mdev_name2uuid(mdev_name):
     """Convert an mdev name (of the form mdev_<uuid_with_underscores>) to a
     uuid (of the form 8-4-4-4-12).