Comment 5 for bug 1978064

2. special answer for MPX

MPX is special as it is not available (other than originally intended) for Icelake and being phased out [1].
The libvirt cpu_map doesn't know about it yet.

For the upstream project or the distribution this isn't as easy as removing the flag (well it might be, but needs to be checked). There are various cross-release and post-upgrade incompatibilities to consider.

Each of them is evaluated separately, this one in fact was already disabled in qemu. So since then mpx is no more really enabled if you use a 4.0 machine type or newer.

Still those issues often have a huge chance for issues hidden underneath and are best resolved consistently across all builds. Therefore one needs to report it upstream which already happened in [3].

Once there is a generally accepted fix to that we will look at its back-portability to different Ubuntu releases.

[1]: https://www.intel.com/content/www/us/en/support/articles/000059823/processors.html
[2]: https://gitlab.com/qemu-project/qemu/-/commit/ecb85fe48cacb2f8740186e81f2f38a2e02bd963
[3]: https://gitlab.com/libvirt/libvirt/-/issues/304