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x86/hyperv: fix for unwanted manipulation of sched_clock when TSC marked unstable

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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>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Tested-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20210713030522.1714803-1-ani@anisinha.ca
Signed-off-by: Wei Liu <wei.liu@kernel.org>
This commit is contained in:
Ani Sinha 2021-07-13 08:35:21 +05:30 committed by Wei Liu
parent ba3f5839fb
commit c445535c3e
1 changed files with 7 additions and 2 deletions
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9
arch/x86/kernel/cpu/mshyperv.c
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@ -375,8 +375,6 @@ 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");
}
/*
@ -437,6 +435,13 @@ 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)