Patch "x86/tsc: Provide 'tsc=unstable' boot parameter" has been added to the 3.18-stable tree

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

x86/tsc: Provide 'tsc=unstable' boot parameter

to the 3.18-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-provide-tsc-unstable-boot-parameter.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Peter Zijlstra <[email protected]>
Date: Thu, 13 Apr 2017 14:56:44 +0200
Subject: x86/tsc: Provide 'tsc=unstable' boot parameter

From: Peter Zijlstra <[email protected]>

[ Upstream commit 8309f86cd41e8714526867177facf7a316d9be53 ]

Since the clocksource watchdog will only detect broken TSC after the fact, all TSC based clocks will likely have observed non-continuous values before/when switching away from TSC.

Therefore only thing to fully avoid random clock movement when your BIOS randomly mucks with TSC values from SMI handlers is reporting the TSC as unstable at boot.

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

@@ -356,6 +356,8 @@ static int __init tsc_setup(char *str)
 		tsc_clocksource_reliable = 1;
 	if (!strncmp(str, "noirqtime", 9))
 		no_sched_irq_time = 1;
+	if (!strcmp(str, "unstable"))
+		mark_tsc_unstable("boot parameter");
 	return 1;
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/perf-core-correct-event-creation-with-perf_format_group.patch queue-3.18/x86-tsc-provide-tsc-unstable-boot-parameter.patch