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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <cd71ecd6-7a3c-05e5-7854-d71763cbc4c2@redhat.com>
Date: Fri, 16 Mar 2018 16:28:20 +0100
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Subject: Re: [Qemu-devel] [PATCH 2/2] i386/kvm: lower requirements for
 Hyper-V frequency MSRs exposure
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To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>, Eduardo Habkost <ehabkost@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, Roman Kagan <rkagan@virtuozzo.com>, qemu-devel@nongnu.org

On 16/03/2018 16:05, Vitaly Kuznetsov wrote:
>>>  
>>> -        if (has_msr_hv_frequencies && tsc_is_stable_and_known(env)) {
>>> +        if (has_msr_hv_frequencies && env->tsc_khz) {
>> Should this be
>>
>> ((env->tsc_khz && has_msr_hv_reenlightenment) ||
>>  tsc_is_stable_and_known(env))
>>
>> so that you don't regress on older kernels?
>>
> I don't actually see where the regression might come from: frequency
> MSRs are supported regardless or reenlightenment/invtsc and there's
> nothing wrong with exposing them but I may be missing something..

On older kernel without re-enlightenment support, you don't want to
expose the frequency MSRs unless invtsc is on, right?

Paolo