Improve default machine type selection

[Jim Fehlig]

On 3/16/23 11:56, Jim Fehlig wrote:
> On 3/15/23 08:40, Ján Tomko wrote:
>> On a Monday in 2023, Jim Fehlig wrote:
>>> If an explicit machine type is not specified in the VM config, the qemu 
>>> driver will select the first machine type in the list of machine types for 
>>> the specified accelerator. See virQEMUCapsGetPreferredMachine
>>>
>>> https://gitlab.com/libvirt/libvirt/-/blob/master/src/qemu/qemu_capabilities.c#L6133
>>>
>>> On my test machines, this works reasonably well for x86_64 where the first 
>>> machine type is pc-i440fx-7.1. But for aarch64, the first machine is 
>>> integratorcp, which is not very useful with maxCpus=1 and other limitations. 
>>
>> Is it possible to run such machine with libvirt?
> 
> I just did a quick check with libvirt 9.1.0 (qemu is a bit older, at 7.1.0):
> 
> # cat test.xml
> <domain type='kvm'>
>    <name>test</name>
>    <memory unit='KiB'>2097152</memory>
>    <vcpu placement='static'>1</vcpu>
>    <os>
>      <type>hvm</type>
>      <loader readonly='yes' 
> type='pflash'>/usr/share/qemu/aavmf-aarch64-code.bin</loader>
>      <nvram template='/usr/share/qemu/aavmf-aarch64-vars.bin'/>
>      <boot dev='hd'/>
>    </os>
>    <clock offset='utc'/>
>    <on_poweroff>destroy</on_poweroff>
>    <on_reboot>restart</on_reboot>
>    <on_crash>destroy</on_crash>
>    <devices>
>      <emulator>/usr/bin/qemu-system-aarch64</emulator>
>      <disk type='file' device='disk'>
>        <driver name='qemu' type='qcow2' discard='unmap'/>
>        <source file='/var/lib/libvirt/images/test.qcow2'/>
>        <target dev='vda' bus='virtio'/>
>      </disk>
>    </devices>
> </domain>

To be fair, this config does not work when specifying machine='virt'

# virsh create test.xml
error: Failed to create domain from test.xml
error: internal error: process exited while connecting to monitor: 
2023-03-16T21:37:30.895916Z qemu-system-aarch64: KVM is not supported for this 
guest CPU type
2023-03-16T21:37:30.895989Z qemu-system-aarch64: kvm_init_vcpu: 
kvm_arch_init_vcpu failed (0): Invalid argument

It worked after adding

<cpu mode='host-passthrough'/>

> # virsh create test.xml
> error: Failed to create domain from test.xml
> error: internal error: Unexpected enum value 0 for virDomainDeviceAddressType
> 

The same error occurs with host-passthrough CPU and default machine type.

Regards,
Jim