This is a note to let you know that I've just added the patch titled

x86/tsc: Future-proof native_calibrate_tsc()

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-tsc-future-proof-native_calibrate_tsc.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From da4ae6c4a0b8dee5a5377a385545d2250fa8cddb Mon Sep 17 00:00:00 2001

From: Len Brown len.brown@intel.com Date: Fri, 22 Dec 2017 00:27:54 -0500 Subject: x86/tsc: Future-proof native_calibrate_tsc()

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

Patches currently in stable-queue which might be from len.brown@intel.com are

queue-4.14/x86-tsc-fix-erroneous-tsc-rate-on-skylake-xeon.patch queue-4.14/x86-tsc-future-proof-native_calibrate_tsc.patch