24 lines
1.2 KiB
YAML
24 lines
1.2 KiB
YAML
---
|
|
features:
|
|
- |
|
|
The libvirt driver now allows specifying individual CPU feature
|
|
flags for guests, via a new configuration attribute
|
|
``[libvirt]/cpu_model_extra_flags`` -- this is valid in combination
|
|
with all the three possible values for ``[libvirt]/cpu_mode``:
|
|
``custom``, ``host-model``, or ``host-passthrough``. The
|
|
``cpu_model_extra_flags`` also allows specifying multiple CPU flags.
|
|
Refer to its documentation in ``nova.conf`` for usage details.
|
|
|
|
One of the motivations for this is to alleviate the performance
|
|
degradation (caused as a result of applying the "Meltdown" CVE
|
|
fixes) for guests running with certain Intel-based virtual CPU
|
|
models. This guest performance impact is reduced by exposing the
|
|
CPU feature flag 'PCID' ("Process-Context ID") to the *guest* CPU,
|
|
assuming that it is available in the physical hardware itself.
|
|
|
|
Note that besides ``custom``, Nova's libvirt driver has two other
|
|
CPU modes: ``host-model`` (which is the default), and
|
|
``host-passthrough``. Refer to the
|
|
``[libvirt]/cpu_model_extra_flags`` documentation for what to do
|
|
when you are using either of those CPU modes in context of 'PCID'.
|