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

Eduardo Habkost
2016-09-28T15:06:01Z

On Wed, Sep 28, 2016 at 05:01:01PM +0200, Paolo Bonzini wrote:
>
>
> On 28/09/2016 16:57, Eduardo Habkost wrote:\
> > This can be fixed by adding actual property names to the
> > FEAT_XSAVE_COMP_* bits. This way we will be able to report
> > meaningful names to management in case GET_SUPPORTED_CPUID says a
> > given xsave component is not supported yet, and will ensure we
> > correctly treat still-unknown xsave components as unmigratable.
>
> 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.

--
Eduardo