Hi Vitaly,
I believe, it is responsibility of each guest code to set X86_FEATURE_TSC_KNOWN_FREQ cap.
Regarding VMware guest, there is a case where vmware_tsc_khz is zero (not provided by hypervisor)
and TSC frequency should be calculated.
Sorry for late response.
Regards,
—Alexey
> On Jan 5, 2021, at 5:06 AM, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote:
>
> Alexey Makhalov <amakhalov@xxxxxxxxxx> writes:
>
>> When TSC frequency is known (retrieved from hypervisor), we should skip
>> TSC refined calibration by setting X86_FEATURE_TSC_KNOWN_FREQ.
>>
>> Signed-off-by: Alexey Makhalov <amakhalov@xxxxxxxxxx>
>> ---
>> arch/x86/kernel/cpu/vmware.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
>> index c6ede3b3d302..83164110ccc5 100644
>> --- a/arch/x86/kernel/cpu/vmware.c
>> +++ b/arch/x86/kernel/cpu/vmware.c
>> @@ -378,6 +378,8 @@ static void __init vmware_set_capabilities(void)
>> {
>> setup_force_cpu_cap(X86_FEATURE_CONSTANT_TSC);
>> setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
>> + if (vmware_tsc_khz)
>> + setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
>> if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMCALL)
>> setup_force_cpu_cap(X86_FEATURE_VMCALL);
>> else if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMMCALL)
>
> The same trick is being used in Xen/Jailhouse/KVM code already and
> Hyper-V overwrites x86_platform.calibrate_tsc/x86_platform.calibrate_cpu
> hooks to basically achive the same goal. Should we maybe introduce a
> flag in 'struct hypervisor_x86' or something like that to unify all
> this?
>
> Just a suggestion.
>
> --
> Vitaly
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