bernardodemarco commented on PR #10964:
URL: https://github.com/apache/cloudstack/pull/10964#issuecomment-3183688837
@rosi-shapeblue, thanks very much for testing!
Basically, Apache CloudStack allows operators to configure the CPU model
that is exposed to VMs in KVM through three properties that can be defined in
`agent.properties`: `guest.cpu.mode`, `guest.cpu.model` and
`guest.cpu.features`.
The `guest.cpu.mode` property accepts three possible values:
- `custom`: Allows the customization of the CPU model, which should be
defined in the `guest.cpu.model` setting. For instance:
```bash
guest.cpu.mode=custom
guest.cpu.model=Skylake-Server
```
The available models for a given architecture can be listed through the
following command:
```bash
virsh cpu-models <architecture>
```
- `host-model`: Libvirt identifies which model is more similar to the host's
CPU model and adds extra features to approximate the host model as closely as
possible.
- `host-passthrough`: Libvirt will communicate to KVM the exact
characteristics of the host's CPU. The main difference from the `host-model`
mode is that instead of pairing CPU flags, all the CPU details from the host
are paired.
The `guest.cpu.features` setting can be used to add or remove individual CPU
features, for instance:
```bash
guest.cpu.mode=custom
guest.cpu.model=Skylake-Server
guest.cpu.features=aes mmx avx
```
As can be noticed from the Agent logs that have been provided:
```bash
2025-08-13 10:35:56,850 WARN [resource.wrapper.LibvirtStartCommandWrapper]
(AgentRequest-Handler-2:[]) (logid:bfd1c45f) LibvirtException
org.libvirt.LibvirtException: XML error: Non-empty feature list specified
without CPU model
```
Libvirt complains about specifying a list of flags without a CPU model.
Therefore, to apply CPU flags in KVM, it is required to meet one of the
following requirements:
- Define `guest.cpu.mode=host-model` and specify the flags;
- Define `guest.cpu.mode=host-passthrough` and specify the flags; or,
- Define `guest.cpu.mode=custom`, `guest.cpu.model=<cpu-model>` and specify
the flags.
Otherwise, Libvirt will complain that a CPU model has not been specified.
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