x86/tsc: Verify TSC_ADJUST from idle
When entering idle, it's a good oportunity to verify that the TSC_ADJUST MSR has not been tampered with (BIOS hiding SMM cycles). If tampering is detected, emit a warning and restore it to the previous value. This is especially important for machines, which mark the TSC reliable because there is no watchdog clocksource available (SoCs). This is not sufficient for HPC (NOHZ_FULL) situations where a CPU never goes idle, but adding a timer to do the check periodically is not an option either. On a machine, which has this issue, the check triggeres right during boot, so there is a decent chance that the sysadmin will notice. Rate limit the check to once per second and warn only once per cpu. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Reviewed-by: NIngo Molnar <mingo@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Yinghai Lu <yinghai@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Link: http://lkml.kernel.org/r/20161119134017.732180441@linutronix.deSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
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