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Date:   Mon, 18 May 2020 10:08:14 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Brian Gerst <brgerst@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Will Deacon <will@kernel.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Wei Liu <wei.liu@kernel.org>,
        Michael Kelley <mikelley@microsoft.com>,
        Jason Chen CJ <jason.cj.chen@intel.com>,
        Zhao Yakui <yakui.zhao@intel.com>
Subject: Re: [patch V6 04/37] x86: Make hardware latency tracing explicit
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On Mon, May 18, 2020 at 10:05:56AM +0200, Thomas Gleixner wrote:
> Peter Zijlstra <peterz@infradead.org> writes:
> > On Sat, May 16, 2020 at 01:45:51AM +0200, Thomas Gleixner wrote:
> >> --- a/arch/x86/kernel/nmi.c
> >> +++ b/arch/x86/kernel/nmi.c
> >> @@ -334,6 +334,7 @@ static noinstr void default_do_nmi(struc
> >>  	__this_cpu_write(last_nmi_rip, regs->ip);
> >>  
> >>  	instrumentation_begin();
> >> +	ftrace_nmi_handler_enter();
> >>  
> >>  	handled = nmi_handle(NMI_LOCAL, regs);
> >>  	__this_cpu_add(nmi_stats.normal, handled);
> >> @@ -420,6 +421,7 @@ static noinstr void default_do_nmi(struc
> >>  		unknown_nmi_error(reason, regs);
> >>  
> >>  out:
> >> +	ftrace_nmi_handler_exit();
> >>  	instrumentation_end();
> >>  }
> >
> > Yeah, so I'm confused about this and the previous patch too. Why not
> > do just this? Remove that ftrace_nmi_handler.* crud from
> > nmi_{enter,exit}() and stick it here? Why do we needs the
> > nmi_{enter,exit}_notrace() thing?
> 
> Because you then have to fixup _all_ architectures which use
> nmi_enter/exit().

We probably have to anyway. But I can do that later I suppose.