Sean Christopherson <seanjc@xxxxxxxxxx> writes:
> +Vitaly
>
> On Thu, Apr 14, 2022, Anton Romanov wrote:
...
>> @@ -8646,9 +8659,12 @@ static void tsc_khz_changed(void *data)
>> struct cpufreq_freqs *freq = data;
>> unsigned long khz = 0;
>>
>> + if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
>> + return;
>
> Vitaly,
>
> The Hyper-V guest code also sets cpu_tsc_khz, should we WARN if that notifier is
> invoked and Hyper-V told us there's a constant TSC?
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ab336f7c82e4..ca8e20f5ffc0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8701,6 +8701,8 @@ static void kvm_hyperv_tsc_notifier(void)
> struct kvm *kvm;
> int cpu;
>
> + WARN_ON_ONCE(boot_cpu_has(X86_FEATURE_CONSTANT_TSC));
> +
> mutex_lock(&kvm_lock);
> list_for_each_entry(kvm, &vm_list, vm_list)
> kvm_make_mclock_inprogress_request(kvm);
>
(apologies for the delayed reply)
No, I think Hyper-V's "Reenlightenment" feature overrides (re-defines?)
X86_FEATURE_CONSTANT_TSC. E.g. I've checked a VM on E5-2667 v4
(Broadwell) CPU with no TSC scaling. This VM has 'constant_tsc' and will
certainly get reenlightenment irq on migration.
Note, Hyper-V has its own 'Invariant TSC control', see commit
dce7cd62754b5 ("x86/hyperv: Allow guests to enable InvariantTSC"). When
enabled, X86_FEATURE_TSC_RELIABLE is forced. I *think* (haven't checked
as I don't have two suitable hosts to test migration handy) this will
suppress reenlightenment so the check should be
WARN_ON_ONCE(boot_cpu_has(X86_FEATURE_TSC_RELIABLE));
instead. There is a chance that reenlightenment notifications still
arrive but the reported 'new' TSC frequency remains unchanged (silly,
but possible), I'll need to check.
--
Vitaly
