4.14-stable review patch. If anyone has any objections, please let me know.
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From: Len Brown len.brown@intel.com
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@intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: peterz@infradead.org Cc: Bin Gao bin.gao@intel.com Link: https://lkml.kernel.org/r/0fe2503aa7d7fc69137141fc705541a78101d2b9.151392041... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- 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