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| author | Ani Sinha <ani@anisinha.ca> | 2021-07-13 08:35:21 +0530 |
|---|---|---|
| committer | Wei Liu <wei.liu@kernel.org> | 2021-07-13 17:40:23 +0000 |
| commit | c445535c3efbfb8cb42d098e624d46ab149664b7 (patch) | |
| tree | 55dc142d1c0f20ceab0b84540b11bf9d3285eeb0 /arch | |
| parent | ba3f5839fbeb3f9e65070d90aa4e66008bbea80f (diff) | |
| download | linux-c445535c3efbfb8cb42d098e624d46ab149664b7.tar.bz2 | |
x86/hyperv: fix for unwanted manipulation of sched_clock when TSC marked unstable
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>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/cpu/mshyperv.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c index cc8f1773deca..8bd1c01c3310 100644 --- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -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) |