[PATCH v6 26/29] x86/watchdog: Add a shim hardlockup detector

[Ricardo Neri]

The generic hardlockup detector is based on perf. It also provides a set
of weak functions that CPU architectures can override. Add a shim
hardlockup detector for x86 that overrides such functions and can
select between perf and HPET implementations of the detector.

For clarity, add the intermediate Kconfig symbol X86_HARDLOCKUP_DETECTOR
that is selected whenever the core of the hardlockup detector is
selected.

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: Nicholas Piggin <npiggin at gmail.com>
Reviewed-by: Tony Luck <tony.luck at intel.com>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon at linux.intel.com>
---
Changes since v5:
 * Added watchdog_nmi_start() to be used when tsc_khz is recalibrated.
 * Always build the x86-specific hardlockup detector shim; not only
   when the HPET-based detector is selected.
 * Corrected a typo in comment in watchdog_nmi_probe() (Ani)
 * Removed useless local ret variable in watchdog_nmi_enable(). (Ani)

Changes since v4:
 * Use a switch to enable and disable the various available detectors.
   (Andi)

Changes since v3:
 * Fixed style in multi-line comment. (Randy Dunlap)

Changes since v2:
 * Pass cpu number as argument to hardlockup_detector_[enable|disable].
   (Thomas Gleixner)

Changes since v1:
 * Introduced this patch: Added an x86-specific shim hardlockup
   detector. (Nicholas Piggin)
---
 arch/x86/Kconfig.debug         |  3 ++
 arch/x86/kernel/Makefile       |  2 +
 arch/x86/kernel/watchdog_hld.c | 85 ++++++++++++++++++++++++++++++++++
 3 files changed, 90 insertions(+)
 create mode 100644 arch/x86/kernel/watchdog_hld.c

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index bc34239589db..599001157847 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -6,6 +6,9 @@ config TRACE_IRQFLAGS_NMI_SUPPORT
 config EARLY_PRINTK_USB
 	bool
 
+config X86_HARDLOCKUP_DETECTOR
+	def_bool y if HARDLOCKUP_DETECTOR_CORE
+
 config X86_VERBOSE_BOOTUP
 	bool "Enable verbose x86 bootup info messages"
 	default y
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index c700b00a2d86..af3d54e4c836 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -114,6 +114,8 @@ obj-$(CONFIG_KGDB)		+= kgdb.o
 obj-$(CONFIG_VM86)		+= vm86_32.o
 obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
 
+obj-$(CONFIG_X86_HARDLOCKUP_DETECTOR) += watchdog_hld.o
+
 obj-$(CONFIG_HPET_TIMER) 	+= hpet.o
 obj-$(CONFIG_X86_HARDLOCKUP_DETECTOR_HPET) += watchdog_hld_hpet.o
 
diff --git a/arch/x86/kernel/watchdog_hld.c b/arch/x86/kernel/watchdog_hld.c
new file mode 100644
index 000000000000..ef11f0af4ef5
--- /dev/null
+++ b/arch/x86/kernel/watchdog_hld.c
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * A shim hardlockup detector. It overrides the weak stubs of the generic
+ * implementation to select between the perf- or the hpet-based implementation.
+ *
+ * Copyright (C) Intel Corporation 2022
+ */
+
+#include <linux/nmi.h>
+#include <asm/hpet.h>
+
+enum x86_hardlockup_detector {
+	X86_HARDLOCKUP_DETECTOR_PERF,
+	X86_HARDLOCKUP_DETECTOR_HPET,
+};
+
+static enum __read_mostly x86_hardlockup_detector detector_type;
+
+int watchdog_nmi_enable(unsigned int cpu)
+{
+	switch (detector_type) {
+	case X86_HARDLOCKUP_DETECTOR_PERF:
+		hardlockup_detector_perf_enable();
+		break;
+	case X86_HARDLOCKUP_DETECTOR_HPET:
+		hardlockup_detector_hpet_enable(cpu);
+		break;
+	default:
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+void watchdog_nmi_disable(unsigned int cpu)
+{
+	switch (detector_type) {
+	case X86_HARDLOCKUP_DETECTOR_PERF:
+		hardlockup_detector_perf_disable();
+		break;
+	case X86_HARDLOCKUP_DETECTOR_HPET:
+		hardlockup_detector_hpet_disable(cpu);
+		break;
+	}
+}
+
+int __init watchdog_nmi_probe(void)
+{
+	int ret;
+
+	/*
+	 * Try first with the HPET hardlockup detector. It will only
+	 * succeed if selected at build time and requested in the
+	 * nmi_watchdog command-line parameter. This ensures that the
+	 * perf-based detector is used by default, if selected at
+	 * build time.
+	 */
+	ret = hardlockup_detector_hpet_init();
+	if (!ret) {
+		detector_type = X86_HARDLOCKUP_DETECTOR_HPET;
+		return ret;
+	}
+
+	ret = hardlockup_detector_perf_init();
+	if (!ret) {
+		detector_type = X86_HARDLOCKUP_DETECTOR_PERF;
+		return ret;
+	}
+
+	return 0;
+}
+
+void watchdog_nmi_stop(void)
+{
+	/* Only the HPET lockup detector defines a stop function. */
+	if (detector_type == X86_HARDLOCKUP_DETECTOR_HPET)
+		hardlockup_detector_hpet_stop();
+}
+
+void watchdog_nmi_start(void)
+{
+	/* Only the HPET lockup detector defines a start function. */
+	if (detector_type == X86_HARDLOCKUP_DETECTOR_HPET)
+		hardlockup_detector_hpet_start();
+}
-- 
2.17.1