Allow cpu_mode to be set to none

It may be desirable to omit the cpu mode altogether. For instance if there
is an emulation bug in one of the cpu features. The previous default of
host-model causes all compatible CPU features to be enabled.

Author: jovial

README.md

@@ -25,6 +25,9 @@ Role Variables
 - `libvirt_vm_emulator`: path to emulator binary. If not set, the role will
   attempt to auto-detect the correct emulator to use.
 
+- `libvirt_cpu_mode_default`: The default CPU mode if `libvirt_cpu_mode` or
+  `vm.cpu_mode` is undefined.
+
 - `libvirt_vm_arch`: CPU architecture, default is `x86_64`.
 
 - `libvirt_vm_uri`: Override the libvirt connection URI. See the
@@ -49,7 +52,8 @@ Role Variables
       `libvirt_vm_engine` is `kvm`, otherwise `pc-1.0`.
 
     - `cpu_mode`: Virtual machine CPU mode. Default is `host-passthrough` if
-      `libvirt_vm_engine` is `kvm`, otherwise `host-model`.
+      `libvirt_vm_engine` is `kvm`, otherwise `host-model`. Can be set to none
+      to not configure a cpu mode.
 
     - `volumes`: a list of volumes to attach to the VM.  Each volume is
       defined with the following dict:

defaults/main.yml

@@ -50,7 +50,7 @@ libvirt_vms:
       machine: "{{ libvirt_vm_machine }}"
 
       # Virtual machine CPU mode.
-      cpu_mode: "{{ libvirt_vm_cpu_mode }}"
+      cpu_mode: "{{ libvirt_vm_cpu_mode | default(libvirt_cpu_mode_default, true) }}"
 
       # List of volumes.
       volumes: "{{ libvirt_vm_volumes }}"
@@ -70,6 +70,9 @@ libvirt_vm_virsh_default_env: "{{  { 'LIBVIRT_DEFAULT_URI': libvirt_vm_uri } if
 # Override for the libvirt connection uri. Leave unset to use the default.
 libvirt_vm_uri: ""
 
+# Default CPU mode if libvirt_vm_cpu_mode or vm.cpu_mode is undefined
+libvirt_cpu_mode_default: "{{ 'host-passthrough' if libvirt_vm_engine == 'kvm' else 'host-model' }}"
+
 ### DEPRECATED ###
 # Use the above settings for each item within `libvirt_vms`, instead of the
 # below deprecated variables.

tasks/main.yml

@@ -31,8 +31,7 @@
          default(libvirt_vm_default_console_log_dir + '/' +  vm.name + '-console.log', true) }}
     machine_default: "{{ none if libvirt_vm_engine == 'kvm' else 'pc-1.0' }}"
     machine: "{{ vm.machine | default(machine_default, true) }}"
-    cpu_mode_default: "{{ 'host-passthrough' if libvirt_vm_engine == 'kvm' else 'host-model' }}"
-    cpu_mode: "{{ vm.cpu_mode | default(cpu_mode_default, true) }}"
+    cpu_mode: "{{ vm.cpu_mode | default(libvirt_cpu_mode_default) }}"
     volumes: "{{ vm.volumes | default([], true) }}"
     interfaces: "{{ vm.interfaces | default([], true) }}"
     start: "{{ vm.start | default(true) }}"