perf/x86/intel: Fix regression by default disabling perfmon v4 interrupt handling

Kyle Huey reported that 'rr', a replay debugger, broke due to the following commit:

  af3bdb99 ("perf/x86/intel: Add a separate Arch Perfmon v4 PMI handler")

Rework the 'disable_counter_freezing' __setup() parameter such that we
can explicitly enable/disable it and switch to default disabled.

To this purpose, rename the parameter to "perf_v4_pmi=" which is a much
better description and allows requiring a bool argument.

[ mingo: Improved the changelog some more. ]
Reported-by: Kyle Huey <me@kylehuey.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert O'Callahan <robert@ocallahan.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: acme@kernel.org
Link: http://lkml.kernel.org/r/20181120170842.GZ2131@hirez.programming.kicks-ass.netSigned-off-by: Ingo Molnar <mingo@kernel.org>

Documentation/admin-guide/kernel-parameters.txt

@@ -856,7 +856,8 @@
 			causing system reset or hang due to sending
 			INIT from AP to BSP.
 
-	disable_counter_freezing [HW]
+	perf_v4_pmi=	[X86,INTEL]
+			Format: <bool>
 			Disable Intel PMU counter freezing feature.
 			The feature only exists starting from
 			Arch Perfmon v4 (Skylake and newer).

arch/x86/events/intel/core.c

@@ -2306,14 +2306,18 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
 	return handled;
 }
 
-static bool disable_counter_freezing;
+static bool disable_counter_freezing = true;
 static int __init intel_perf_counter_freezing_setup(char *s)
 {
-	disable_counter_freezing = true;
-	pr_info("Intel PMU Counter freezing feature disabled\n");
+	bool res;
+
+	if (kstrtobool(s, &res))
+		return -EINVAL;
+
+	disable_counter_freezing = !res;
 	return 1;
 }
-__setup("disable_counter_freezing", intel_perf_counter_freezing_setup);
+__setup("perf_v4_pmi=", intel_perf_counter_freezing_setup);
 
 /*
  * Simplified handler for Arch Perfmon v4: