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Re: [Qemu-devel] [PATCH v2 1/2] i386/kvm: add support for Hyper-V reenli


From: Roman Kagan
Subject: Re: [Qemu-devel] [PATCH v2 1/2] i386/kvm: add support for Hyper-V reenlightenment MSRs
Date: Mon, 19 Mar 2018 20:06:03 +0300
User-agent: Mutt/1.9.2 (2017-12-15)

On Fri, Mar 16, 2018 at 06:00:19PM +0100, Vitaly Kuznetsov wrote:
> KVM recently gained support for Hyper-V Reenlightenment MSRs which are
> required to make KVM-on-Hyper-V enable TSC page clocksource to its guests
> when INVTSC is not passed to it (and it is not passed by default in Qemu
> as it effectively blocks migration).
> 
> Signed-off-by: Vitaly Kuznetsov <address@hidden>
> ---
> Changes since v1:
> - add vmstate_msr_hyperv_reenlightenment subsection to vmstate_x86_cpu
>   [Paolo Bonzini]
> ---
>  target/i386/cpu.h          |  3 +++
>  target/i386/hyperv-proto.h |  9 ++++++++-
>  target/i386/kvm.c          | 33 +++++++++++++++++++++++++++++++++
>  target/i386/machine.c      | 24 ++++++++++++++++++++++++
>  4 files changed, 68 insertions(+), 1 deletion(-)
> 
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 2e2bab5ff3..0b1b556a56 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -1174,6 +1174,9 @@ typedef struct CPUX86State {
>      uint64_t msr_hv_synic_sint[HV_SINT_COUNT];
>      uint64_t msr_hv_stimer_config[HV_STIMER_COUNT];
>      uint64_t msr_hv_stimer_count[HV_STIMER_COUNT];
> +    uint64_t msr_hv_reenlightenment_control;
> +    uint64_t msr_hv_tsc_emulation_control;
> +    uint64_t msr_hv_tsc_emulation_status;
>  
>      uint64_t msr_rtit_ctrl;
>      uint64_t msr_rtit_status;
> diff --git a/target/i386/hyperv-proto.h b/target/i386/hyperv-proto.h
> index cb4d7f2b7a..93352ebd2a 100644
> --- a/target/i386/hyperv-proto.h
> +++ b/target/i386/hyperv-proto.h
> @@ -35,7 +35,7 @@
>  #define HV_RESET_AVAILABLE           (1u << 7)
>  #define HV_REFERENCE_TSC_AVAILABLE   (1u << 9)
>  #define HV_ACCESS_FREQUENCY_MSRS     (1u << 11)
> -
> +#define HV_ACCESS_REENLIGHTENMENTS_CONTROL  (1u << 13)
>  
>  /*
>   * HV_CPUID_FEATURES.EDX bits
> @@ -129,6 +129,13 @@
>  #define HV_X64_MSR_CRASH_CTL                    0x40000105
>  #define HV_CRASH_CTL_NOTIFY                     (1ull << 63)
>  
> +/*
> + * Reenlightenment notification MSRs
> + */
> +#define HV_X64_MSR_REENLIGHTENMENT_CONTROL      0x40000106
> +#define HV_X64_MSR_TSC_EMULATION_CONTROL        0x40000107
> +#define HV_X64_MSR_TSC_EMULATION_STATUS         0x40000108
> +
>  /*
>   * Hypercall status code
>   */
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index d23fff12f5..accf50eac3 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -90,6 +90,7 @@ static bool has_msr_hv_runtime;
>  static bool has_msr_hv_synic;
>  static bool has_msr_hv_stimer;
>  static bool has_msr_hv_frequencies;
> +static bool has_msr_hv_reenlightenment;
>  static bool has_msr_xss;
>  static bool has_msr_spec_ctrl;
>  static bool has_msr_smi_count;
> @@ -653,6 +654,11 @@ static int hyperv_handle_properties(CPUState *cs)
>              env->features[FEAT_HYPERV_EAX] |= HV_ACCESS_FREQUENCY_MSRS;
>              env->features[FEAT_HYPERV_EDX] |= HV_FREQUENCY_MSRS_AVAILABLE;
>          }
> +
> +        if (has_msr_hv_reenlightenment) {
> +            env->features[FEAT_HYPERV_EAX] |=
> +                HV_ACCESS_REENLIGHTENMENTS_CONTROL;
> +        }

Can you please add a matching comment to the definition of
feature_word_info[FEAT_HYPERV_EAX].feat_names[]?

Also there appears to be no cpu property to turn this on/off, does it?
It's enabled based only on the support in the KVM it's running against.
So I guess we may have a problem migrating between the hosts with
different KVM versions, one supporting it and the other not.
(This is also a problem with has_msr_hv_frequencies, and is in general a
long-standing issue of hv_* properties being done differently from the
rest of CPUID features.)

Thanks,
Roman.



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