4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Len Brown <len.brown@xxxxxxxxx> commit da4ae6c4a0b8dee5a5377a385545d2250fa8cddb upstream. If the crystal frequency cannot be determined via CPUID(15).crystal_khz or the built-in table then native_calibrate_tsc() will still set the X86_FEATURE_TSC_KNOWN_FREQ flag which prevents the refined TSC calibration. As a consequence such systems use cpu_khz for the TSC frequency which is incorrect when cpu_khz != tsc_khz resulting in time drift. Return early when the crystal frequency cannot be retrieved without setting the X86_FEATURE_TSC_KNOWN_FREQ flag. This ensures that the refined TSC calibration is invoked. [ tglx: Steam-blastered changelog. Sigh ] Fixes: 4ca4df0b7eb0 ("x86/tsc: Mark TSC frequency determined by CPUID as known") Signed-off-by: Len Brown <len.brown@xxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: peterz@xxxxxxxxxxxxx Cc: Bin Gao <bin.gao@xxxxxxxxx> Link: https://lkml.kernel.org/r/0fe2503aa7d7fc69137141fc705541a78101d2b9.1513920414.git.len.brown@xxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kernel/tsc.c | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -612,6 +612,8 @@ unsigned long native_calibrate_tsc(void) } } + if (crystal_khz == 0) + return 0; /* * TSC frequency determined by CPUID is a "hardware reported" * frequency and is the most accurate one so far we have. This