Re: [PATCH v4 05/27] x86: Replace ist_enter() with nmi_enter()

[Steven Rostedt]

On Mon, 24 Feb 2020 22:31:39 +0100
Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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