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Date:   Sat, 16 May 2020 01:45:51 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [patch V6 04/37] x86: Make hardware latency tracing explicit


The hardware latency tracer calls into trace_sched_clock and ends up in
various instrumentable functions which is problemeatic vs. the kprobe
handling especially the text poke machinery. It's invoked from
nmi_enter/exit(), i.e. non-instrumentable code.

Use nmi_enter/exit_notrace() instead. These variants do not invoke the
hardware latency tracer which avoids chasing down complex callchains to
make them non-instrumentable.

The real interesting measurement is the actual NMI handler. Add an explicit
invocation for the hardware latency tracer to it.

#DB and #BP are uninteresting as they really should not be in use when
analzying hardware induced latencies.

If #DF hits, hardware latency is definitely not interesting anymore and in
case of a machine check the hardware latency is not the most troublesome
issue either.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

---
 arch/x86/kernel/cpu/mce/core.c |    4 ++--
 arch/x86/kernel/nmi.c          |    6 ++++--
 arch/x86/kernel/traps.c        |   12 +++++++-----
 3 files changed, 13 insertions(+), 9 deletions(-)

--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1916,7 +1916,7 @@ static __always_inline void exc_machine_
 	    mce_check_crashing_cpu())
 		return;
 
-	nmi_enter();
+	nmi_enter_notrace();
 	/*
 	 * The call targets are marked noinstr, but objtool can't figure
 	 * that out because it's an indirect call. Annotate it.
@@ -1924,7 +1924,7 @@ static __always_inline void exc_machine_
 	instrumentation_begin();
 	machine_check_vector(regs);
 	instrumentation_end();
-	nmi_exit();
+	nmi_exit_notrace();
 }
 
 static __always_inline void exc_machine_check_user(struct pt_regs *regs)
--- 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();
 }
 
@@ -536,14 +538,14 @@ DEFINE_IDTENTRY_NMI(exc_nmi)
 	}
 #endif
 
-	nmi_enter();
+	nmi_enter_notrace();
 
 	inc_irq_stat(__nmi_count);
 
 	if (!ignore_nmis)
 		default_do_nmi(regs);
 
-	nmi_exit();
+	nmi_exit_notrace();
 
 #ifdef CONFIG_X86_64
 	if (unlikely(this_cpu_read(update_debug_stack))) {
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -387,7 +387,7 @@ DEFINE_IDTENTRY_DF(exc_double_fault)
 	}
 #endif
 
-	nmi_enter();
+	nmi_enter_notrace();
 	instrumentation_begin();
 	notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);
 
@@ -632,12 +632,14 @@ DEFINE_IDTENTRY_RAW(exc_int3)
 		instrumentation_end();
 		idtentry_exit(regs);
 	} else {
-		nmi_enter();
+		nmi_enter_notrace();
 		instrumentation_begin();
+		ftrace_nmi_handler_enter();
 		if (!do_int3(regs))
 			die("int3", regs, 0);
+		ftrace_nmi_handler_exit();
 		instrumentation_end();
-		nmi_exit();
+		nmi_exit_notrace();
 	}
 }
 
@@ -849,7 +851,7 @@ static void noinstr handle_debug(struct
 static __always_inline void exc_debug_kernel(struct pt_regs *regs,
 					     unsigned long dr6)
 {
-	nmi_enter();
+	nmi_enter_notrace();
 	/*
 	 * The SDM says "The processor clears the BTF flag when it
 	 * generates a debug exception."  Clear TIF_BLOCKSTEP to keep
@@ -871,7 +873,7 @@ static __always_inline void exc_debug_ke
 	if (dr6)
 		handle_debug(regs, dr6, false);
 
-	nmi_exit();
+	nmi_exit_notrace();
 }
 
 static __always_inline void exc_debug_user(struct pt_regs *regs,

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