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Re: [Qemu-devel] [PATCH] i386/kvm: expose HV_CPUID_ENLIGHTMENT_INFO.EAX
From: |
Vitaly Kuznetsov |
Subject: |
Re: [Qemu-devel] [PATCH] i386/kvm: expose HV_CPUID_ENLIGHTMENT_INFO.EAX and HV_CPUID_NESTED_FEATURES.EAX as feature words |
Date: |
Thu, 29 Nov 2018 12:51:55 +0100 |
Paolo Bonzini <address@hidden> writes:
> On 26/11/18 14:59, Vitaly Kuznetsov wrote:
>> It was found that QMP users of QEMU (e.g. libvirt) may need
>> HV_CPUID_ENLIGHTMENT_INFO.EAX/HV_CPUID_NESTED_FEATURES.EAX information. In
>> particular, 'hv_tlbflush' and 'hv_evmcs' enlightenments are only exposed in
>> HV_CPUID_ENLIGHTMENT_INFO.EAX.
>>
>> HV_CPUID_NESTED_FEATURES.EAX is exposed for two reasons: convenience
>> (we don't need to export it from hyperv_handle_properties() and as
>> future-proof for Enlightened MSR-Bitmap, PV EPT invalidation and
>> direct virtual flush features.
>>
>> Signed-off-by: Vitaly Kuznetsov <address@hidden>
>
> Can you add a comment to feature_word_info, explaining why the
> feat_names are not set?
I had to do some code archeology to make sure I understand, I think it
goes back to
http://lists.gnu.org/archive/html/qemu-devel/2016-06/msg06579.html
So the comment (probably added before FEAT_HYPERV_EAX definition) would
be
".feat_names are commented out for Hyper-V enlightenments because we
don't want to have two different ways for enabling them on QEMU command
line. Some features (e.g. "hyperv_time", "hyperv_vapic", ...) require
enabling several feature bits simultaneously, exposing these bits
individually may just confuse guests."
Would do?
--
Vitaly