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authorLen Brown <len.brown@intel.com>2017-12-22 08:27:54 +0300
committerThomas Gleixner <tglx@linutronix.de>2018-01-14 14:14:50 +0300
commitda4ae6c4a0b8dee5a5377a385545d2250fa8cddb (patch)
tree89ea6b232881a8a4238229e08194f33ca841390a /arch/x86/kernel/tsc.c
parent9f15b9120f562ae0bf0a836c96f4dafb33ae426a (diff)
downloadlinux-da4ae6c4a0b8dee5a5377a385545d2250fa8cddb.tar.xz
x86/tsc: Future-proof native_calibrate_tsc()
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> Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/0fe2503aa7d7fc69137141fc705541a78101d2b9.1513920414.git.len.brown@intel.com
Diffstat (limited to 'arch/x86/kernel/tsc.c')
-rw-r--r--arch/x86/kernel/tsc.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 8ea117f8142e..ce4b71119c36 100644
--- 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