On Fri, Aug 4, 2017 at 3:39 PM, David Hildenbrand <david@xxxxxxxxxx> wrote:
> On 04.08.2017 11:14, Ladi Prosek wrote:
>> As of kernel commit eb82feea59d6 ("KVM: hyperv: support HV_X64_MSR_TSC_FREQUENCY
>> and HV_X64_MSR_APIC_FREQUENCY"), KVM supports two new MSRs which are required
>> for nested Hyper-V to read timestamps with RDTSC + TSC page.
>>
>> This commit makes QEMU advertise the MSRs with CPUID.40000003H:EAX[11] and
>> CPUID.40000003H:EDX[8] as specified in the Hyper-V TLFS and experimentally
>> verified on a Hyper-V host. The feature is enabled with the existing hv-time CPU
>> flag, and only if the TSC frequency is stable across migration and known.
>>
>> Signed-off-by: Ladi Prosek <lprosek@xxxxxxxxxx>
>> ---
>> target/i386/kvm.c | 16 +++++++++++++++-
>> 1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
>> index 77b6373..7e484a7 100644
>> --- a/target/i386/kvm.c
>> +++ b/target/i386/kvm.c
>> @@ -89,6 +89,7 @@ static bool has_msr_hv_vpindex;
>> 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_xss;
>>
>> static bool has_msr_architectural_pmu;
>> @@ -631,7 +632,17 @@ static int hyperv_handle_properties(CPUState *cs)
>> if (cpu->hyperv_time) {
>> env->features[FEAT_HYPERV_EAX] |= HV_X64_MSR_HYPERCALL_AVAILABLE;
>> env->features[FEAT_HYPERV_EAX] |= HV_X64_MSR_TIME_REF_COUNT_AVAILABLE;
>> - env->features[FEAT_HYPERV_EAX] |= 0x200;
>> + env->features[FEAT_HYPERV_EAX] |= HV_X64_MSR_REFERENCE_TSC_AVAILABLE;
>> + if (has_msr_hv_frequencies> + /* TSC clock must be stable and known for this feature. */
>> + && ((env->features[FEAT_8000_0007_EDX] & CPUID_APM_INVTSC)
>> + || env->user_tsc_khz != 0)
>> + && env->tsc_khz != 0) {
>
> I'd drop the != 0 in both cases and move the env->tsc_khz check up to
> has_msr_hv_frequencies.
>
> if (has_msr_hv_frequencies && env->tsc_khz && ...
>
> Wonder if it even would make sense to move some parts of this check into
> a helper function, to beautify this a bit. tsc_stable(env)
> tsc_known(env) ...
Yup, especially since I copied these conditions from "if
(cpu->vmware_cpuid_freq .." further down in the file. So maybe one
helper called by both would be the best. Thanks!
>> +
>> + env->features[FEAT_HYPERV_EAX] |= HV_X64_ACCESS_FREQUENCY_MSRS;
>> + env->features[FEAT_HYPERV_EDX] |=
>> + HV_FEATURE_FREQUENCY_MSRS_AVAILABLE;
>> + }
>> }
>> if (cpu->hyperv_crash && has_msr_hv_crash) {
>> env->features[FEAT_HYPERV_EDX] |= HV_X64_GUEST_CRASH_MSR_AVAILABLE;
>> @@ -1127,6 +1138,9 @@ static int kvm_get_supported_msrs(KVMState *s)
>> case HV_X64_MSR_STIMER0_CONFIG:
>> has_msr_hv_stimer = true;
>> break;
>> + case HV_X64_MSR_TSC_FREQUENCY:
>> + has_msr_hv_frequencies = true;
>> + break;
>> }
>>
>> }
>>
>
>
> --
>
> Thanks,
>
> David
