[PATCH v6 29/29] x86/tsc: Switch to perf-based hardlockup detector if TSC become unstable

[Ricardo Neri]

The HPET-based hardlockup detector relies on the TSC to determine if an
observed NMI interrupt was originated by HPET timer. Hence, this detector
can no longer be used with an unstable TSC.

In such case, permanently stop the HPET-based hardlockup detector and
start the perf-based detector.

Cc: Andi Kleen <ak at linux.intel.com>
Cc: Stephane Eranian <eranian at google.com>
Cc: "Ravi V. Shankar" <ravi.v.shankar at intel.com>
Cc: iommu at lists.linux-foundation.org
Cc: linuxppc-dev at lists.ozlabs.org
Cc: x86 at kernel.org
Suggested-by: Thomas Gleixner <tglx at linutronix.de>
Reviewed-by: Tony Luck <tony.luck at intel.com>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon at linux.intel.com>
---
Changes since v5:
 * Relocated the delcaration of hardlockup_detector_switch_to_perf() to
   x86/nmi.h It does not depend on HPET.
 * Removed function stub. The shim hardlockup detector is always for x86.

Changes since v4:
 * Added a stub version of hardlockup_detector_switch_to_perf() for
   !CONFIG_HPET_TIMER. (lkp)
 * Reconfigure the whole lockup detector instead of unconditionally
   starting the perf-based hardlockup detector.

Changes since v3:
 * None

Changes since v2:
 * Introduced this patch.

Changes since v1:
 * N/A
---
 arch/x86/include/asm/nmi.h     | 6 ++++++
 arch/x86/kernel/tsc.c          | 2 ++
 arch/x86/kernel/watchdog_hld.c | 6 ++++++
 3 files changed, 14 insertions(+)

diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h
index 4a0d5b562c91..47752ff67d8b 100644
--- a/arch/x86/include/asm/nmi.h
+++ b/arch/x86/include/asm/nmi.h
@@ -63,4 +63,10 @@ void stop_nmi(void);
 void restart_nmi(void);
 void local_touch_nmi(void);
 
+#ifdef CONFIG_X86_HARDLOCKUP_DETECTOR
+void hardlockup_detector_switch_to_perf(void);
+#else
+static inline void hardlockup_detector_switch_to_perf(void) { }
+#endif
+
 #endif /* _ASM_X86_NMI_H */
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index cc1843044d88..74772ffc79d1 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1176,6 +1176,8 @@ void mark_tsc_unstable(char *reason)
 
 	clocksource_mark_unstable(&clocksource_tsc_early);
 	clocksource_mark_unstable(&clocksource_tsc);
+
+	hardlockup_detector_switch_to_perf();
 }
 
 EXPORT_SYMBOL_GPL(mark_tsc_unstable);
diff --git a/arch/x86/kernel/watchdog_hld.c b/arch/x86/kernel/watchdog_hld.c
index ef11f0af4ef5..7940977c6312 100644
--- a/arch/x86/kernel/watchdog_hld.c
+++ b/arch/x86/kernel/watchdog_hld.c
@@ -83,3 +83,9 @@ void watchdog_nmi_start(void)
 	if (detector_type == X86_HARDLOCKUP_DETECTOR_HPET)
 		hardlockup_detector_hpet_start();
 }
+
+void hardlockup_detector_switch_to_perf(void)
+{
+	detector_type = X86_HARDLOCKUP_DETECTOR_PERF;
+	lockup_detector_reconfigure();
+}
-- 
2.17.1