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Re: [Qemu-devel] [PATCH v4 2/2] i386/kvm: expose Hyper-V frequency MSRs
From: |
Eduardo Habkost |
Subject: |
Re: [Qemu-devel] [PATCH v4 2/2] i386/kvm: expose Hyper-V frequency MSRs with reenlightenment |
Date: |
Thu, 22 Mar 2018 15:49:33 -0300 |
User-agent: |
Mutt/1.9.2 (2017-12-15) |
On Thu, Mar 22, 2018 at 02:13:58PM +0100, Vitaly Kuznetsov wrote:
> We can also expose Hyper-V frequency MSRs when reenlightenment feature is
> enabled and TSC frequency is known, Hyper-V on KVM will provide stable TSC
> page clocksources to its guests.
>
> Signed-off-by: Vitaly Kuznetsov <address@hidden>
> ---
> - Expose frequency MSRs only when either INVTSC or Reenlightenment is
> provided [Paolo Bonzini]
> ---
> target/i386/kvm.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 75f4e1d69e..2c3c19d690 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -651,7 +651,8 @@ static int hyperv_handle_properties(CPUState *cs)
> env->features[FEAT_HYPERV_EAX] |= HV_TIME_REF_COUNT_AVAILABLE;
> env->features[FEAT_HYPERV_EAX] |= HV_REFERENCE_TSC_AVAILABLE;
>
> - if (has_msr_hv_frequencies && tsc_is_stable_and_known(env)) {
> + if (has_msr_hv_frequencies && env->tsc_khz &&
Why is the check for env->tsc_khz necessary?
Are there known circumstances where HV_X64_MSR_TSC_FREQUENCY will be supported
by KVM but ioctl(KVM_GET_TSC_KHZ) will return 0, or this is just for extra
safety?
> + (tsc_is_stable_and_known(env) || cpu->hyperv_reenlightenment)) {
> env->features[FEAT_HYPERV_EAX] |= HV_ACCESS_FREQUENCY_MSRS;
> env->features[FEAT_HYPERV_EDX] |= HV_FREQUENCY_MSRS_AVAILABLE;
> }
> --
> 2.14.3
>
--
Eduardo