Date:   Wed, 01 Dec 2021 23:47:04 -0000
From:   "tip-bot2 for Feng Tang" <tip-bot2@linutronix.de>
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To:     linux-tip-commits@vger.kernel.org
Subject: [tip: x86/urgent] x86/tsc: Add a timer to make sure TSC_adjust is
 always checked
Cc:     Feng Tang <feng.tang@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Paul E. McKenney" <paulmck@kernel.org>, stable@vger.kernel.org,
        x86@kernel.org, linux-kernel@vger.kernel.org
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The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     c7719e79347803b8e3b6b50da8c6db410a3012b5
Gitweb:        https://git.kernel.org/tip/c7719e79347803b8e3b6b50da8c6db410a3012b5
Author:        Feng Tang <feng.tang@intel.com>
AuthorDate:    Wed, 17 Nov 2021 10:37:50 +08:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 02 Dec 2021 00:40:35 +01:00

x86/tsc: Add a timer to make sure TSC_adjust is always checked

The TSC_ADJUST register is checked every time a CPU enters idle state, but
Thomas Gleixner mentioned there is still a caveat that a system won't enter
idle [1], either because it's too busy or configured purposely to not enter
idle.

Setup a periodic timer (every 10 minutes) to make sure the check is
happening on a regular base.

[1] https://lore.kernel.org/lkml/875z286xtk.fsf@nanos.tec.linutronix.de/

Fixes: 6e3cd95234dc ("x86/hpet: Use another crystalball to evaluate HPET usability")
Requested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211117023751.24190-1-feng.tang@intel.com

---
 arch/x86/kernel/tsc_sync.c | 41 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+)

diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c
index 50a4515..9452dc9 100644
--- a/arch/x86/kernel/tsc_sync.c
+++ b/arch/x86/kernel/tsc_sync.c
@@ -30,6 +30,7 @@ struct tsc_adjust {
 };
 
 static DEFINE_PER_CPU(struct tsc_adjust, tsc_adjust);
+static struct timer_list tsc_sync_check_timer;
 
 /*
  * TSC's on different sockets may be reset asynchronously.
@@ -77,6 +78,46 @@ void tsc_verify_tsc_adjust(bool resume)
 	}
 }
 
+/*
+ * Normally the tsc_sync will be checked every time system enters idle
+ * state, but there is still caveat that a system won't enter idle,
+ * either because it's too busy or configured purposely to not enter
+ * idle.
+ *
+ * So setup a periodic timer (every 10 minutes) to make sure the check
+ * is always on.
+ */
+
+#define SYNC_CHECK_INTERVAL		(HZ * 600)
+
+static void tsc_sync_check_timer_fn(struct timer_list *unused)
+{
+	int next_cpu;
+
+	tsc_verify_tsc_adjust(false);
+
+	/* Run the check for all onlined CPUs in turn */
+	next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
+	if (next_cpu >= nr_cpu_ids)
+		next_cpu = cpumask_first(cpu_online_mask);
+
+	tsc_sync_check_timer.expires += SYNC_CHECK_INTERVAL;
+	add_timer_on(&tsc_sync_check_timer, next_cpu);
+}
+
+static int __init start_sync_check_timer(void)
+{
+	if (!cpu_feature_enabled(X86_FEATURE_TSC_ADJUST) || tsc_clocksource_reliable)
+		return 0;
+
+	timer_setup(&tsc_sync_check_timer, tsc_sync_check_timer_fn, 0);
+	tsc_sync_check_timer.expires = jiffies + SYNC_CHECK_INTERVAL;
+	add_timer(&tsc_sync_check_timer);
+
+	return 0;
+}
+late_initcall(start_sync_check_timer);
+
 static void tsc_sanitize_first_cpu(struct tsc_adjust *cur, s64 bootval,
 				   unsigned int cpu, bool bootcpu)
 {