[tip:perf/urgent] perf/x86/intel: Fix regression by default disabling perfmon v4 interrupt handling

[tip-bot for Peter Zijlstra]

Commit-ID:  2a5bf23d5b795d5df33dc284e8f5cf8b6a5b4042
Gitweb:     https://git.kernel.org/tip/2a5bf23d5b795d5df33dc284e8f5cf8b6a5b4042
Author:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Tue, 20 Nov 2018 18:08:42 +0100
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 20 Nov 2018 18:57:48 +0100

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:

  af3bdb991a5c ("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@xxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Robert O'Callahan <robert@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Cc: acme@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20181120170842.GZ2131@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 Documentation/admin-guide/kernel-parameters.txt |  3 ++-
 arch/x86/events/intel/core.c                    | 12 ++++++++----
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 81d1d5a74728..5463d5a4d85c 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/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).
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 273c62e81546..af8bea9d4006 100644
--- a/arch/x86/events/intel/core.c
+++ b/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: