Re: [Qemu-devel] [PATCH v3 1/2] i386/kvm: add support for Hyper-V reenlightenment MSRs

[Marcelo Tosatti <mtosatti@redhat.com>]

On Tue, Mar 20, 2018 at 06:34:59PM +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).

Hi Vitaly,

>From Microsoft's documentation:

"An L1 hypervisor can request to be notified when its partition is
migrated. This capability is enumerated in CPUID as
AccessReenlightenmentControls privilege (see 2.4.10)."

The L0 hypervisor exposes a synthetic MSR
(HV_X64_MSR_REENLIGHTENMENT_CONTROL) that may be used by the L1
hypervisor to configure an interrupt vector and target processor. The L0
hypervisor will inject an interrupt with the specified vector after each
migration.

What prevents a guest from setting the enable bit, and expect
to receive an interrupt, if the reenlightenment MSRs are exposed ?

> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> Changes since v2:
> - add hv-reenlightenment CPU property [Roman Kagan, Paolo Bonzini]
> - add a comment to feature_word_info [Roman Kagan]
> ---
>  target/i386/cpu.c          |  4 +++-
>  target/i386/cpu.h          |  4 ++++
>  target/i386/hyperv-proto.h |  9 ++++++++-
>  target/i386/kvm.c          | 39 ++++++++++++++++++++++++++++++++++++++-
>  target/i386/machine.c      | 24 ++++++++++++++++++++++++
>  5 files changed, 77 insertions(+), 3 deletions(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 6bb4ce8719..02579f8234 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -407,7 +407,8 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
>              NULL /* hv_vpindex_access */, NULL /* hv_msr_reset_access */,
>              NULL /* hv_msr_stats_access */, NULL /* hv_reftsc_access */,
>              NULL /* hv_msr_idle_access */, NULL /* hv_msr_frequency_access */,
> -            NULL, NULL, NULL, NULL,
> +            NULL /* hv_msr_debug_access */, NULL /* hv_msr_reenlightenment_access */,
> +            NULL, NULL,
>              NULL, NULL, NULL, NULL,
>              NULL, NULL, NULL, NULL,
>              NULL, NULL, NULL, NULL,
> @@ -4764,6 +4765,7 @@ static Property x86_cpu_properties[] = {
>      DEFINE_PROP_BOOL("hv-runtime", X86CPU, hyperv_runtime, false),
>      DEFINE_PROP_BOOL("hv-synic", X86CPU, hyperv_synic, false),
>      DEFINE_PROP_BOOL("hv-stimer", X86CPU, hyperv_stimer, false),
> +    DEFINE_PROP_BOOL("hv-reenlightenment", X86CPU, hyperv_reenlightenment, false),
>      DEFINE_PROP_BOOL("check", X86CPU, check_cpuid, true),
>      DEFINE_PROP_BOOL("enforce", X86CPU, enforce_cpuid, false),
>      DEFINE_PROP_BOOL("kvm", X86CPU, expose_kvm, true),
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 2e2bab5ff3..98eed72937 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;
> @@ -1296,6 +1299,7 @@ struct X86CPU {
>      bool hyperv_runtime;
>      bool hyperv_synic;
>      bool hyperv_stimer;
> +    bool hyperv_reenlightenment;
>      bool check_cpuid;
>      bool enforce_cpuid;
>      bool expose_kvm;
> 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..7d9f9ca0b1 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;
> @@ -583,7 +584,8 @@ static bool hyperv_enabled(X86CPU *cpu)
>              cpu->hyperv_vpindex ||
>              cpu->hyperv_runtime ||
>              cpu->hyperv_synic ||
> -            cpu->hyperv_stimer);
> +            cpu->hyperv_stimer ||
> +            cpu->hyperv_reenlightenment);
>  }
>  
>  static int kvm_arch_set_tsc_khz(CPUState *cs)
> @@ -654,6 +656,14 @@ static int hyperv_handle_properties(CPUState *cs)
>              env->features[FEAT_HYPERV_EDX] |= HV_FREQUENCY_MSRS_AVAILABLE;
>          }
>      }
> +    if (cpu->hyperv_reenlightenment) {
> +        if (!has_msr_hv_reenlightenment) {
> +            fprintf(stderr,
> +                    "Hyper-V Reenlightenment is not supported by kernel\n");
> +            return -ENOSYS;
> +        }
> +        env->features[FEAT_HYPERV_EAX] |= HV_ACCESS_REENLIGHTENMENTS_CONTROL;
> +    }
>      if (cpu->hyperv_crash && has_msr_hv_crash) {
>          env->features[FEAT_HYPERV_EDX] |= HV_GUEST_CRASH_MSR_AVAILABLE;
>      }
> @@ -1185,6 +1195,9 @@ static int kvm_get_supported_msrs(KVMState *s)
>                  case HV_X64_MSR_TSC_FREQUENCY:
>                      has_msr_hv_frequencies = true;
>                      break;
> +                case HV_X64_MSR_REENLIGHTENMENT_CONTROL:
> +                    has_msr_hv_reenlightenment = true;
> +                    break;
>                  case MSR_IA32_SPEC_CTRL:
>                      has_msr_spec_ctrl = true;
>                      break;
> @@ -1747,6 +1760,15 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
>              if (cpu->hyperv_time) {
>                  kvm_msr_entry_add(cpu, HV_X64_MSR_REFERENCE_TSC,
>                                    env->msr_hv_tsc);
> +
> +                if (has_msr_hv_reenlightenment) {
> +                    kvm_msr_entry_add(cpu, HV_X64_MSR_REENLIGHTENMENT_CONTROL,
> +                                      env->msr_hv_reenlightenment_control);
> +                    kvm_msr_entry_add(cpu, HV_X64_MSR_TSC_EMULATION_CONTROL,
> +                                      env->msr_hv_tsc_emulation_control);
> +                    kvm_msr_entry_add(cpu, HV_X64_MSR_TSC_EMULATION_STATUS,
> +                                      env->msr_hv_tsc_emulation_status);
> +                }
>              }
>          }
>          if (cpu->hyperv_vapic) {
> @@ -2109,6 +2131,12 @@ static int kvm_get_msrs(X86CPU *cpu)
>      }
>      if (cpu->hyperv_time) {
>          kvm_msr_entry_add(cpu, HV_X64_MSR_REFERENCE_TSC, 0);
> +
> +        if (has_msr_hv_reenlightenment) {
> +            kvm_msr_entry_add(cpu, HV_X64_MSR_REENLIGHTENMENT_CONTROL, 0);
> +            kvm_msr_entry_add(cpu, HV_X64_MSR_TSC_EMULATION_CONTROL, 0);
> +            kvm_msr_entry_add(cpu, HV_X64_MSR_TSC_EMULATION_STATUS, 0);
> +        }
>      }
>      if (has_msr_hv_crash) {
>          int j;
> @@ -2367,6 +2395,15 @@ static int kvm_get_msrs(X86CPU *cpu)
>              env->msr_hv_stimer_count[(index - HV_X64_MSR_STIMER0_COUNT)/2] =
>                                  msrs[i].data;
>              break;
> +        case HV_X64_MSR_REENLIGHTENMENT_CONTROL:
> +            env->msr_hv_reenlightenment_control = msrs[i].data;
> +            break;
> +        case HV_X64_MSR_TSC_EMULATION_CONTROL:
> +            env->msr_hv_tsc_emulation_control = msrs[i].data;
> +            break;
> +        case HV_X64_MSR_TSC_EMULATION_STATUS:
> +            env->msr_hv_tsc_emulation_status = msrs[i].data;
> +            break;
>          case MSR_MTRRdefType:
>              env->mtrr_deftype = msrs[i].data;
>              break;
> diff --git a/target/i386/machine.c b/target/i386/machine.c
> index bd2d82e91b..fd99c0bbb4 100644
> --- a/target/i386/machine.c
> +++ b/target/i386/machine.c
> @@ -713,6 +713,29 @@ static const VMStateDescription vmstate_msr_hyperv_stimer = {
>      }
>  };
>  
> +static bool hyperv_reenlightenment_enable_needed(void *opaque)
> +{
> +    X86CPU *cpu = opaque;
> +    CPUX86State *env = &cpu->env;
> +
> +    return env->msr_hv_reenlightenment_control != 0 ||
> +        env->msr_hv_tsc_emulation_control != 0 ||
> +        env->msr_hv_tsc_emulation_status != 0;
> +}
> +
> +static const VMStateDescription vmstate_msr_hyperv_reenlightenment = {
> +    .name = "cpu/msr_hyperv_reenlightenment",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = hyperv_reenlightenment_enable_needed,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UINT64(env.msr_hv_reenlightenment_control, X86CPU),
> +        VMSTATE_UINT64(env.msr_hv_tsc_emulation_control, X86CPU),
> +        VMSTATE_UINT64(env.msr_hv_tsc_emulation_status, X86CPU),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
>  static bool avx512_needed(void *opaque)
>  {
>      X86CPU *cpu = opaque;
> @@ -1005,6 +1028,7 @@ VMStateDescription vmstate_x86_cpu = {
>          &vmstate_msr_hyperv_runtime,
>          &vmstate_msr_hyperv_synic,
>          &vmstate_msr_hyperv_stimer,
> +        &vmstate_msr_hyperv_reenlightenment,
>          &vmstate_avx512,
>          &vmstate_xss,
>          &vmstate_tsc_khz,
> -- 
> 2.14.3