Patch "x86/tsc: Fix ART for TSC_KNOWN_FREQ" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

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

    x86/tsc: Fix ART for TSC_KNOWN_FREQ

to the 4.9-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-fix-art-for-tsc_known_freq.patch
and it can be found in the queue-4.9 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 44fee88cea43d3c2cac962e0439cb10a3cabff6d Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Mon, 13 Mar 2017 15:57:12 +0100
Subject: x86/tsc: Fix ART for TSC_KNOWN_FREQ

From: Peter Zijlstra <peterz@infradead.org>

commit 44fee88cea43d3c2cac962e0439cb10a3cabff6d upstream.

Subhransu reported that convert_art_to_tsc() isn't working for him.

The ART to TSC relation is only set up for systems which use the refined
TSC calibration. Systems with known TSC frequency (available via CPUID 15)
are not using the refined calibration and therefor the ART to TSC relation
is never established.

Add the setup to the known frequency init path which skips ART
calibration. The init code needs to be duplicated as for systems which use
refined calibration the ART setup must be delayed until calibration has
been done.

The problem has been there since the ART support was introdduced, but only
detected now because Subhransu tested the first time on hardware which has
TSC frequency enumerated via CPUID 15.

Note for stable: The conditional has changed from TSC_RELIABLE to
     	 	 TSC_KNOWN_FREQUENCY.

[ tglx: Rewrote changelog and identified the proper 'Fixes' commit ]

Fixes: f9677e0f8308 ("x86/tsc: Always Running Timer (ART) correlated clocksource")
Reported-by: "Prusty, Subhransu S" <subhransu.s.prusty@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Cc: christopher.s.hall@intel.com
Cc: kevin.b.stanton@intel.com
Cc: john.stultz@linaro.org
Cc: akataria@vmware.com
Link: http://lkml.kernel.org/r/20170313145712.GI3312@twins.programming.kicks-ass.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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
@@ -1287,6 +1287,8 @@ static int __init init_tsc_clocksource(v
 	 * exporting a reliable TSC.
 	 */
 	if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) {
+		if (boot_cpu_has(X86_FEATURE_ART))
+			art_related_clocksource = &clocksource_tsc;
 		clocksource_register_khz(&clocksource_tsc, tsc_khz);
 		return 0;
 	}


Patches currently in stable-queue which might be from peterz@infradead.org are

queue-4.9/futex-fix-potential-use-after-free-in-futex_requeue_pi.patch
queue-4.9/futex-add-missing-error-handling-to-futex_requeue_pi.patch
queue-4.9/x86-perf-fix-cr4.pce-propagation-to-use-active_mm-instead-of-mm.patch
queue-4.9/locking-rwsem-fix-down_write_killable-for-config_rwsem_generic_spinlock-y.patch
queue-4.9/x86-tsc-fix-art-for-tsc_known_freq.patch