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

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.