From 121ce20c06a79987648bc65d09b992cec3a5c265 Mon Sep 17 00:00:00 2001 From: Len Brown Date: Fri, 22 Dec 2017 00:27:54 -0500 Subject: [PATCH] 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: 66bd0156b8ab ("x86/tsc: Mark TSC frequency determined by CPUID as known") Signed-off-by: Len Brown Signed-off-by: Thomas Gleixner Cc: peterz@infradead.org Cc: Bin Gao 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 8ea117f8142e1..ce4b71119c362 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 -- 2.39.5