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 <stable@xxxxxxxxxxxxxxx> know about it.
>From da4ae6c4a0b8dee5a5377a385545d2250fa8cddb Mon Sep 17 00:00:00 2001
From: Len Brown <len.brown@xxxxxxxxx>
Date: Fri, 22 Dec 2017 00:27:54 -0500
Subject: x86/tsc: Future-proof native_calibrate_tsc()
From: Len Brown <len.brown@xxxxxxxxx>
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@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: peterz@xxxxxxxxxxxxx
Cc: Bin Gao <bin.gao@xxxxxxxxx>
Link: https://lkml.kernel.org/r/0fe2503aa7d7fc69137141fc705541a78101d2b9.1513920414.git.len.brown@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxx 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