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

Paolo Bonzini
2016-09-28T16:07:17Z

On 28/09/2016 17:59, Eduardo Habkost wrote:
> On Wed, Sep 28, 2016 at 05:09:46PM +0200, Paolo Bonzini wrote:
>>
>>
>> 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.
>
> Yes, this makes sense. If XSTATE_YMM_BIT is missing, for example,
> it is more useful to say "avx" is unsupported by the host, than
> something like "xsave-component-ymm".

So instead of looking at wi->feat_names[i] we could have a wrapper that
returns the name and special cases xsave components words? This should
be used in both x86_cpu_get_migratable_flags and
report_unavailable_features, but not elsewhere as far as I could see.

Paolo