[PATCH 07/17] stop_machine: Add stop_cluster_cpuslocked() for per-cluster operations

[Ehab Ababneh]

From: Qiuxu Zhuo <qiuxu.zhuo@xxxxxxxxx>

There is already stop_core_cpuslocked() for hardware core-level testing
features, which requires near-simultaneous execution of the WRMSR
instruction on all threads of a core to initiate a test. However, some
hardware requires this simultaneous execution of WRMSR at the cluster
level.

Add stop_cluster_cpuslocked(), a customized version of
stop_machine_cpuslocked() for operating solely on the threads of a
single cluster.

Suggested-by: Tony Luck <tony.luck@xxxxxxxxx>
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@xxxxxxxxx>
Signed-off-by: Ehab Ababneh <ehab.ababneh@xxxxxxxxx>
---
 include/linux/stop_machine.h | 15 +++++++++++++++
 kernel/stop_machine.c        | 35 ++++++++++++++++++++++-------------
 2 files changed, 37 insertions(+), 13 deletions(-)

diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h
index 84e7fb627ba4..a189f405a4f2 100644
--- a/include/linux/stop_machine.h
+++ b/include/linux/stop_machine.h
@@ -157,6 +157,21 @@ int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data, const struct cpumask *
  */
 int stop_core_cpuslocked(unsigned int cpu, cpu_stop_fn_t fn, void *data);
 
+/**
+ * stop_cluster_cpuslocked: - stop all threads on a CPU cluster
+ * @cpu: any CPU in the targeted cluster
+ * @fn: the function to run
+ * @data: the data ptr for @fn()
+ *
+ * Same as above, only the CPUs associated with a single CPU cluster are affected.
+ *
+ * Context: Must be called from within a cpus_read_lock() protected region.
+ *
+ * Return: 0 if all executions of @fn returned 0, any non zero return
+ * value if any returned non zero.
+ */
+int stop_cluster_cpuslocked(unsigned int cpu, cpu_stop_fn_t fn, void *data);
+
 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
 				   const struct cpumask *cpus);
 #else	/* CONFIG_SMP || CONFIG_HOTPLUG_CPU */
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index d085ba1f4b44..1afda0ddfb90 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -630,32 +630,41 @@ int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
 }
 EXPORT_SYMBOL_GPL(stop_machine);
 
-#ifdef CONFIG_SCHED_SMT
-/*
- * INTEL_IFS is the only user of this API. That selftest can
- * only be compiled if SMP=y. On x86 it selects SCHED_SMT.
- * Keep the ifdefs for now.
- */
-int stop_core_cpuslocked(unsigned int cpu, cpu_stop_fn_t fn, void *data)
+static int stop_cpus_cpuslocked(const struct cpumask *cpus, cpu_stop_fn_t fn, void *data)
 {
-	const struct cpumask *smt_mask = cpu_smt_mask(cpu);
-
 	struct multi_stop_data msdata = {
 		.fn = fn,
 		.data = data,
-		.num_threads = cpumask_weight(smt_mask),
-		.active_cpus = smt_mask,
+		.num_threads = cpumask_weight(cpus),
+		.active_cpus = cpus,
 	};
 
 	lockdep_assert_cpus_held();
 
-	/* Set the initial state and stop all online cpus. */
+	/* Set the initial state and stop all online @cpus. */
 	set_state(&msdata, MULTI_STOP_PREPARE);
-	return stop_cpus(smt_mask, multi_cpu_stop, &msdata);
+	return stop_cpus(cpus, multi_cpu_stop, &msdata);
+}
+
+#ifdef CONFIG_SCHED_SMT
+/*
+ * INTEL_IFS is the only user of this API. That selftest can
+ * only be compiled if SMP=y. On x86 it selects SCHED_SMT.
+ * Keep the ifdefs for now.
+ */
+int stop_core_cpuslocked(unsigned int cpu, cpu_stop_fn_t fn, void *data)
+{
+	return stop_cpus_cpuslocked(cpu_smt_mask(cpu), fn, data);
 }
 EXPORT_SYMBOL_GPL(stop_core_cpuslocked);
 #endif
 
+int stop_cluster_cpuslocked(unsigned int cpu, cpu_stop_fn_t fn, void *data)
+{
+	return stop_cpus_cpuslocked(topology_cluster_cpumask(cpu), fn, data);
+}
+EXPORT_SYMBOL_GPL(stop_cluster_cpuslocked);
+
 /**
  * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
  * @fn: the function to run
-- 
2.43.0