Re: [PATCH 3/3] i386: Make sure kvm_arch_set_tsc_khz() succeeds on migration when 'hv-reenlightenment' was exposed

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Vitaly Kuznetsov (vkuznets@redhat.com) wrote:
> KVM doesn't fully support Hyper-V reenlightenment notifications on
> migration. In particular, it doesn't support emulating TSC frequency
> of the source host by trapping all TSC accesses so unless TSC scaling
> is supported on the destination host and KVM_SET_TSC_KHZ succeeds, it
> is unsafe to proceed with migration.
> 
> Normally, we only require KVM_SET_TSC_KHZ to succeed when 'user_tsc_khz'
> was set and just 'try' KVM_SET_TSC_KHZ without otherwise.
> 
> Introduce a new vmstate section (which is added when the guest has
> reenlightenment feature enabled) and add env.tsc_khz to it. We already
> have env.tsc_khz packed in 'cpu/tsc_khz' but we don't want to be dependent
> on the section order.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  target/i386/kvm/hyperv.h |  1 +
>  target/i386/kvm/kvm.c    | 11 +++++++++++
>  target/i386/machine.c    | 37 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 49 insertions(+)
> 
> diff --git a/target/i386/kvm/hyperv.h b/target/i386/kvm/hyperv.h
> index 67543296c3a4..c65e5c85c4d3 100644
> --- a/target/i386/kvm/hyperv.h
> +++ b/target/i386/kvm/hyperv.h
> @@ -20,6 +20,7 @@
>  
>  #ifdef CONFIG_KVM
>  int kvm_hv_handle_exit(X86CPU *cpu, struct kvm_hyperv_exit *exit);
> +int kvm_hv_tsc_frequency_loaded(X86CPU *cpu);
>  #endif
>  
>  int hyperv_x86_synic_add(X86CPU *cpu);
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index 7fe9f527103c..f6c4093778e9 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -1460,6 +1460,17 @@ static int hyperv_init_vcpu(X86CPU *cpu)
>      return 0;
>  }
>  
> +int kvm_hv_tsc_frequency_loaded(X86CPU *cpu)
> +{
> +    CPUState *cs = CPU(cpu);
> +
> +    /*
> +     * KVM doens't fully support re-enlightenment notifications so we need to
                 ^^
tpyo

Dave

> +     * make sure TSC frequency doesn't change upon migration.
> +     */
> +    return kvm_arch_set_tsc_khz(cs);
> +}
> +
>  static Error *invtsc_mig_blocker;
>  
>  #define KVM_MAX_CPUID_ENTRIES  100
> diff --git a/target/i386/machine.c b/target/i386/machine.c
> index 715620c58809..369a8f1e7a7a 100644
> --- a/target/i386/machine.c
> +++ b/target/i386/machine.c
> @@ -896,6 +896,42 @@ static const VMStateDescription vmstate_msr_hyperv_reenlightenment = {
>          VMSTATE_END_OF_LIST()
>      }
>  };
> +
> +static bool hyperv_tsc_frequency_needed(void *opaque)
> +{
> +    X86CPU *cpu = opaque;
> +    CPUX86State *env = &cpu->env;
> +
> +    return env->tsc_khz != 0 && (env->msr_hv_reenlightenment_control ||
> +                                 env->msr_hv_tsc_emulation_control);
> +}
> +
> +static int hyperv_tsc_frequency_post_load(void *opaque, int version_id)
> +{
> +    X86CPU *cpu = opaque;
> +    int r;
> +
> +    r = kvm_hv_tsc_frequency_loaded(cpu);
> +    if (r) {
> +        error_report("Failed to set the desired TSC frequency and "
> +                     "reenlightenment was exposed");
> +        return -EINVAL;
> +    }
> +
> +    return 0;
> +}
> +
> +static const VMStateDescription vmstate_msr_hyperv_tsc_frequency = {
> +    .name = "cpu/msr_hyperv_tsc_frequency",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = hyperv_tsc_frequency_needed,
> +    .post_load = hyperv_tsc_frequency_post_load,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_INT64(env.tsc_khz, X86CPU),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
>  #endif
>  
>  static bool avx512_needed(void *opaque)
> @@ -1495,6 +1531,7 @@ VMStateDescription vmstate_x86_cpu = {
>          &vmstate_msr_hyperv_synic,
>          &vmstate_msr_hyperv_stimer,
>          &vmstate_msr_hyperv_reenlightenment,
> +        &vmstate_msr_hyperv_tsc_frequency,
>  #endif
>          &vmstate_avx512,
>          &vmstate_xss,
> -- 
> 2.30.2
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK