3.18-stable review patch. If anyone has any objections, please let me know.
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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; }