Messages in this thread Patch in this message | | | Date | Sun, 14 Jan 2018 03:43:19 -0800 | From | tip-bot for Len Brown <> | Subject | [tip:x86/urgent] x86/tsc: Future-proof native_calibrate_tsc() |
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Commit-ID: da4ae6c4a0b8dee5a5377a385545d2250fa8cddb Gitweb: https://git.kernel.org/tip/da4ae6c4a0b8dee5a5377a385545d2250fa8cddb Author: Len Brown <len.brown@intel.com> AuthorDate: Fri, 22 Dec 2017 00:27:54 -0500 Committer: Thomas Gleixner <tglx@linutronix.de> CommitDate: Sun, 14 Jan 2018 12:14:50 +0100
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
--- arch/x86/kernel/tsc.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 8ea117f..ce4b711 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
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