[libvirt] [PATCH RESEND v1 1/2] i386: Add Intel Processor Trace feature support
luwei.kang at intel.com
Tue Jan 16 06:10:17 UTC 2018
> > 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. 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,
> > > or it will have no way to find out if a feature is migration-safe or
> > > not.
> > ...
> > >  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.
> Oh, now I see that the x86 code uses
> QEMU_MONITOR_CPU_MODEL_EXPANSION_STATIC_FULL and not just QEMU_MONITOR_CPU_MODEL_EXPANSION_FULL. Nice!
So, I need to add Intel PT feature in "X86CPUDefinition builtin_x86_defs" so that we can get this CPUID in specific CPU model not only "-cpu host". Is that right?
Intel PT is first supported in Intel Core M and 5th generation Intel Core processors that are based on the Intel micro-architecture code name Broadwell but Intel PT use EPT is first supported in Ice Lake. Intel PT virtualization depend on PT use EPT. I will add Intel PT to "Broadwell" CPU model and later to make sure a "Broadwell" guest can use Intel PT if the host is Ice Lake.
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