From mboxrd@z Thu Jan  1 00:00:00 1970
From: Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH v4 05/27] x86: Replace ist_enter() with nmi_enter()
Date: Mon, 24 Feb 2020 17:02:31 -0500
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>, LKML <linux-kernel@vger.kernel.org>, linux-arch <linux-arch@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>, Joel Fernandes <joel@joelfernandes.org>, Greg KH <gregkh@linuxfoundation.org>, gustavo@embeddedor.com, Thomas Gleixner <tglx@linutronix.de>, paulmck@kernel.org, Josh Triplett <josh@joshtriplett.org>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Lai Jiangshan <jiangshanlai@gmail.com>, Tony Luck <tony.luck@intel.com>, Frederic Weisbecker <frederic@kernel.org>, Dan Carpenter <dan.carpenter@oracle.com>, Masami Hiramatsu <mhiramat@kernel.org>

On Mon, 24 Feb 2020 22:31:39 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> > Just want to confirm that printk_nmi_enter(), lockdep_off(),
> > and ftrace_nmi_enter() are all marked fully with NOKPROBE.  
> 
> *sigh*, right you are, I only looked at notrace, not nokprobe.
> 
> In particular the ftrace one is a bit off a mess, let me sort through
> that.

ftrace_nmi_enter() has two purposes. One, for archs that need to deal with
NMIs while they still use stop machine. Although, it appears sh is the only
arch that does that. I can look to see if it can be ripped out.

The other is for the hwlat detector that measures the time it was in an
NMI, as NMIs appear as a hardware latency too.

-- Steve