From: Ani Sinha ani@anisinha.ca
[ Upstream commit c445535c3efbfb8cb42d098e624d46ab149664b7 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/cpu/mshyperv.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c index c890d67a64ad..ba54c44a64e2 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)