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author | Ani Sinha <ani@anisinha.ca> | 2021-07-13 08:35:21 +0530 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-09-18 13:40:17 +0200 |
commit | 871abd1e6185fa0e066ced9ef8b7a517388f18e8 (patch) | |
tree | fe3b623b555a6bf6a7c5dd51cbb600eb45666a35 /arch | |
parent | c327b69e96b0d17b56ebf15ebdf3262148f7e7af (diff) | |
download | linux-stable-871abd1e6185fa0e066ced9ef8b7a517388f18e8.tar.gz linux-stable-871abd1e6185fa0e066ced9ef8b7a517388f18e8.tar.bz2 linux-stable-871abd1e6185fa0e066ced9ef8b7a517388f18e8.zip |
x86/hyperv: fix for unwanted manipulation of sched_clock when TSC marked unstable
[ 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>
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 6cc50ab07bde..65d11711cd7b 100644 --- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -322,8 +322,6 @@ 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"); } /* @@ -382,6 +380,13 @@ 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"); } const __initconst struct hypervisor_x86 x86_hyper_ms_hyperv = { |