Patch "x86/tsc: Future-proof native_calibrate_tsc()" has been added to the 4.14-stable tree

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;a=summary

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 <[email protected]> know about it.

From: Len Brown <[email protected]>
Date: Fri, 22 Dec 2017 00:27:54 -0500
Subject: x86/tsc: Future-proof native_calibrate_tsc()

From: Len Brown <[email protected]>

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 ]

---
 arch/x86/kernel/tsc.c |    2 ++
 1 file changed, 2 insertions(+)

@@ -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 [email protected] 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