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

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

[gregkh]

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 <stable@vger.kernel.org> know about it.


>From foo@baz Tue Apr 10 13:58:07 CEST 2018
From: Peter Zijlstra <peterz@infradead.org>
Date: Thu, 13 Apr 2017 14:56:44 +0200
Subject: x86/tsc: Provide 'tsc=unstable' boot parameter

From: Peter Zijlstra <peterz@infradead.org>


[ 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.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
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
@@ -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 peterz@infradead.org 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