libvirt: check for AMD SEV only on x86-64

"kernel doesn't support AMD SEV" message on aarch64 does not make sense

Closes-bug: #1873012
Change-Id: I1ae22197dc68751938f524d823f39e5c89cec7b0

nova/tests/unit/virt/libvirt/test_host.py

@@ -1342,6 +1342,21 @@ class TestLibvirtSEVUnsupported(TestLibvirtSEV):
     def test_unsupported_with_feature(self, fake_exists):
         self.assertFalse(self.host.supports_amd_sev)
 
+    def test_non_x86_architecture(self):
+        fake_caps_xml = '''
+<capabilities>
+  <host>
+    <uuid>cef19ce0-0ca2-11df-855d-b19fbce37686</uuid>
+    <cpu>
+      <arch>aarch64</arch>
+    </cpu>
+  </host>
+</capabilities>'''
+        with mock.patch.object(fakelibvirt.virConnect, 'getCapabilities',
+                               return_value=fake_caps_xml):
+            self.host._set_amd_sev_support()
+            self.assertFalse(self.host.supports_amd_sev)
+
 
 class TestLibvirtSEVSupported(TestLibvirtSEV):
     """Libvirt driver tests for when AMD SEV support is present."""

nova/virt/libvirt/host.py

@@ -51,6 +51,7 @@ import nova.conf
 from nova import context as nova_context
 from nova import exception
 from nova.i18n import _
+from nova.objects import fields
 from nova import rpc
 from nova import utils
 from nova.virt import event as virtevent
@@ -1273,6 +1274,10 @@ class Host(object):
     def _set_amd_sev_support(self):
         self._supports_amd_sev = False
 
+        caps = self.get_capabilities()
+        if caps.host.cpu.arch != fields.Architecture.X86_64:
+            return
+
         if not self._kernel_supports_amd_sev():
             LOG.info("kernel doesn't support AMD SEV")
             self._supports_amd_sev = False