linux-kernel - [RFC PATCH v5 13/16] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter

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Message-Id: <20210504190526.22347-14-ricardo.neri-calderon@linux.intel.com>
Date:   Tue,  4 May 2021 12:05:23 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>
Cc:     "H. Peter Anvin" <hpa@...or.com>, Ashok Raj <ashok.raj@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Nicholas Piggin <npiggin@...il.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephane Eranian <eranian@...gle.com>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Andi Kleen <andi.kleen@...el.com>
Subject: [RFC PATCH v5 13/16] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter

Keep the HPET-based hardlockup detector disabled unless explicitly enabled
via a command-line argument. If such parameter is not given, the
initialization of the hpet-based hardlockup detector fails and the NMI
watchdog will fall back to use the perf-based implementation.

Implement the command-line parsing using an early_param, as
__setup("nmi_watchdog=") only parses generic options.

Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ashok Raj <ashok.raj@...el.com>
Cc: Andi Kleen <andi.kleen@...el.com>
Cc: Tony Luck <tony.luck@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: "Ravi V. Shankar" <ravi.v.shankar@...el.com>
Cc: x86@...nel.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
--
Changes since v4:
 * None

Changes since v3:
 * None

Changes since v2:
 * Do not imply that using nmi_watchdog=hpet means the detector is
   enabled. Instead, print a warning in such case.

Changes since v1:
 * Added documentation to the function handing the nmi_watchdog
   kernel command-line argument.
---
 .../admin-guide/kernel-parameters.txt         |  8 ++++++-
 arch/x86/kernel/watchdog_hld_hpet.c           | 22 +++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 74db44ce4d9a..eafa38867270 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3136,7 +3136,7 @@
 			Format: [state][,regs][,debounce][,die]
 
 	nmi_watchdog=	[KNL,BUGS=X86] Debugging features for SMP kernels
-			Format: [panic,][nopanic,][num]
+			Format: [panic,][nopanic,][num,][hpet]
 			Valid num: 0 or 1
 			0 - turn hardlockup detector in nmi_watchdog off
 			1 - turn hardlockup detector in nmi_watchdog on
@@ -3147,6 +3147,12 @@
 			please see 'nowatchdog'.
 			This is useful when you use a panic=... timeout and
 			need the box quickly up again.
+			When hpet is specified, the NMI watchdog will be driven
+			by an HPET timer, if available in the system. Otherwise,
+			it falls back to the default implementation (perf or
+			architecture-specific). Specifying hpet has no effect
+			if the NMI watchdog is not enabled (either at build time
+			or via the command line).
 
 			These settings can be accessed at runtime via
 			the nmi_watchdog and hardlockup_panic sysctls.
diff --git a/arch/x86/kernel/watchdog_hld_hpet.c b/arch/x86/kernel/watchdog_hld_hpet.c
index cd5f59b7c01b..3fd2405b31fa 100644
--- a/arch/x86/kernel/watchdog_hld_hpet.c
+++ b/arch/x86/kernel/watchdog_hld_hpet.c
@@ -548,6 +548,28 @@ void hardlockup_detector_hpet_stop(void)
 	disable_timer(hld_data);
 }
 
+/**
+ * hardlockup_detector_hpet_setup() - Parse command-line parameters
+ * @str:	A string containing the kernel command line
+ *
+ * Parse the nmi_watchdog parameter from the kernel command line. If
+ * selected by the user, use this implementation to detect hardlockups.
+ */
+static int __init hardlockup_detector_hpet_setup(char *str)
+{
+	if (!str)
+		return -EINVAL;
+
+	if (parse_option_str(str, "hpet"))
+		hardlockup_use_hpet = true;
+
+	if (!nmi_watchdog_user_enabled && hardlockup_use_hpet)
+		pr_err("Selecting HPET NMI watchdog has no effect with NMI watchdog disabled\n");
+
+	return 0;
+}
+early_param("nmi_watchdog", hardlockup_detector_hpet_setup);
+
 /**
  * hardlockup_detector_hpet_init() - Initialize the hardlockup detector
  *
-- 
2.17.1