[libvirt] [PATCH RESEND v1 1/2] i386: Add Intel Processor Trace feature support

[Jiri Denemark]

On Mon, Jan 15, 2018 at 12:04:55 -0200, Eduardo Habkost wrote:
> CCing libvirt developers.
...
> This case is slightly more problematic, however: the new feature
> is actually migratable (under very controlled circumstances)
> because of patch 2/2, but it is not migration-safe[1].  This
> means libvirt shouldn't include it in "host-model" expansion
> (which uses the query-cpu-model-expansion QMP command) until we
> make the feature migration-safe.
> 
> For QEMU, this means the feature shouldn't be returned by
> "query-cpu-model-expansion type=static model=max" (but it can be
> returned by "query-cpu-model-expansion type=full model=max").
> 
> Jiri, it looks like libvirt uses type=full on
> query-cpu-model-expansion on x86.  It needs to use
> type=static[2], or it will have no way to find out if a feature
> is migration-safe or not.
...
> [2] It looks like libvirt uses type=full because it wants to get
>     all QOM property aliases returned.  In this case, one
>     solution for libvirt is to use:
> 
>     static_expansion = query_cpu_model_expansion(type=static, model)
>     all_props = query_cpu_model_expansion(type=full, static_expansion)

This is exactly what libvirt is doing (with model = "host") ever since
query-cpu-model-expansion support was implemented for x86.

Jirka