Re: [Qemu-devel] [PATCH] target-i386: fix losing XCR0 processor state component bits

[Paolo Bonzini]

On 28/09/2016 17:05, Eduardo Habkost wrote:
> > Hmm, right.  Even though XSAVE could be migrated as a blob, QEMU
> > marshals and unmarshals the registers out and back into the xsave data,
> > so that unknown features are indeed unmigratable.
> > 
> > But are the property names necessary?  It makes no sense to
> > enable/disable XSAVE components separately from the other CPUID bits
> > that enable them.  Could we just mark all unknown features as
> > unmigratable without giving them names?
>
> We could, as we don't really need to make them configurable. But
> giving them names will also allow us to return more useful data
> to libvirt in case GET_SUPPORTED_CPUID returns some bits as
> unsupported. The new CPU runnability/comparison APIs are all
> based on property names.

The names could, or perhaps should, be obtained also from
x86_ext_save_areas (apart from the legacy x87 and sse components which
are guaranteed to be there).  Basically property names such as "avx"
trigger both the regular CPUID bits and the XSAVE components.

Paolo