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References: <20180312151233.16565-1-vkuznets@redhat.com>
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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <7d1afa27-9653-75dc-ebfe-8633b93f1ce6@redhat.com>
Date: Fri, 16 Mar 2018 15:49:30 +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>, Richard Henderson <rth@twiddle.net>, Eduardo Habkost <ehabkost@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>
Cc: Roman Kagan <rkagan@virtuozzo.com>, qemu-devel@nongnu.org

On 12/03/2018 16:12, 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?

Paolo

>              env->features[FEAT_HYPERV_EAX] |= HV_ACCESS_FREQUENCY_MSRS;
>              env->features[FEAT_HYPERV_EDX] |= HV_FREQUENCY_MSRS_AVAILABLE;
>          }