4.14-stable review patch. If anyone has any objections, please let me know.
------------------
From: Len Brown <len.br...@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.br...@intel.com>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Cc: pet...@infradead.org
Cc: Bin Gao <bin....@intel.com>
Link:
https://lkml.kernel.org/r/0fe2503aa7d7fc69137141fc705541a78101d2b9.1513920414.git.len.br...@intel.com
Signed-off-by: Greg Kroah-Hartman <gre...@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
