Messages in this thread Patch in this message | | | From | Ani Sinha <> | Subject | [PATCH] Hyper-V: fix for unwanted manipulation of sched_clock when TSC marked unstable | Date | Tue, 13 Jul 2021 08:35:21 +0530 |
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Marking TSC as unstable has a side effect of marking sched_clock as unstable when TSC is still being used as the sched_clock. This is not desirable. Hyper-V ultimately uses a paravirtualized clock source that provides a stable scheduler clock even on systems without TscInvariant CPU capability. Hence, mark_tsc_unstable() call should be called _after_ scheduler clock has been changed to the paravirtualized clocksource. This will prevent any unwanted manipulation of the sched_clock. Only TSC will be correctly marked as unstable.
Signed-off-by: Ani Sinha <ani@anisinha.ca> --- arch/x86/kernel/cpu/mshyperv.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c index 22f13343b5da..715458b7729a 100644 --- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -370,8 +370,6 @@ static void __init ms_hyperv_init_platform(void) if (ms_hyperv.features & HV_ACCESS_TSC_INVARIANT) { wrmsrl(HV_X64_MSR_TSC_INVARIANT_CONTROL, 0x1); setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE); - } else { - mark_tsc_unstable("running on Hyper-V"); } /* @@ -432,6 +430,12 @@ static void __init ms_hyperv_init_platform(void) /* Register Hyper-V specific clocksource */ hv_init_clocksource(); #endif + /* TSC should be marked as unstable only after Hyper-V + * clocksource has been initialized. This ensures that the + * stability of the sched_clock is not altered. + */ + if (!(ms_hyperv.features & HV_ACCESS_TSC_INVARIANT)) + mark_tsc_unstable("running on Hyper-V"); } static bool __init ms_hyperv_x2apic_available(void) -- 2.25.1
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