[PATCH] arm64: implement arm64 specific cpu_to_node

[Huang Shijie]

After setting the right NUMA node for VMAP stack,
  https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?id=75b5e0bf90bf

I found there are at least four places in the common code where
the cpu_to_node() is called before it is initialized:
   0.) early_trace_init()         in kernel/trace/trace.c
   1.) sched_init()               in kernel/sched/core.c
   2.) init_sched_fair_class()    in kernel/sched/fair.c
   3.) workqueue_init_early()     in kernel/workqueue.c

We cannot use early_cpu_to_node() for them, since early_cpu_to_node()
does not work for some ARCHs, such as x86, riscv, etc.

So we have to implement the arm64 specific cpu_to_node().
This patch
   0.) introduces the __cpu_to_node function pointer,
       and exports it for kernel modules.

   1.) defines a macro cpu_to_node to override the
       generic percpu implementation of cpu_to_node.

   2.) __cpu_to_node is initialized with early_cpu_to_node() before
       numa_node is initialized.

   3.) __cpu_to_node is set to arm64_cpu_to_node() when numa_node is ready.
      arm64_cpu_to_node() is a clone of the generic cpu_to_node().

Signed-off-by: Huang Shijie <shijie at os.amperecomputing.com>
---
 arch/arm64/include/asm/topology.h |  4 ++++
 arch/arm64/kernel/smp.c           | 21 ++++++++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/topology.h b/arch/arm64/include/asm/topology.h
index a323b109b9c4..3e99b40b5f9f 100644
--- a/arch/arm64/include/asm/topology.h
+++ b/arch/arm64/include/asm/topology.h
@@ -12,6 +12,10 @@ int pcibus_to_node(struct pci_bus *bus);
 				 cpu_all_mask :				\
 				 cpumask_of_node(pcibus_to_node(bus)))
 
+/* override generic percpu implementation of cpu_to_node */
+extern int (*__cpu_to_node)(int cpu);
+#define cpu_to_node(cpu) __cpu_to_node(cpu)
+
 #endif /* CONFIG_NUMA */
 
 #include <linux/arch_topology.h>
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 4ced34f62dab..8a3bc101eaed 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -90,6 +90,21 @@ static struct irq_desc *ipi_desc[MAX_IPI] __ro_after_init;
 
 static void ipi_setup(int cpu);
 
+int (*__cpu_to_node)(int cpu);
+EXPORT_SYMBOL(__cpu_to_node);
+
+#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
+static int arm64_cpu_to_node(int cpu)
+{
+	return per_cpu(numa_node, cpu);
+}
+#else
+static int arm64_cpu_to_node(int cpu)
+{
+	return 0;
+}
+#endif
+
 #ifdef CONFIG_HOTPLUG_CPU
 static void ipi_teardown(int cpu);
 static int op_cpu_kill(unsigned int cpu);
@@ -613,6 +628,7 @@ static void __init acpi_parse_and_init_cpus(void)
 
 	for (i = 0; i < nr_cpu_ids; i++)
 		early_map_cpu_to_node(i, acpi_numa_get_nid(i));
+	__cpu_to_node = early_cpu_to_node;
 }
 #else
 #define acpi_parse_and_init_cpus(...)	do { } while (0)
@@ -674,6 +690,7 @@ static void __init of_parse_and_init_cpus(void)
 next:
 		cpu_count++;
 	}
+	__cpu_to_node = early_cpu_to_node;
 }
 
 /*
@@ -733,7 +750,7 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 	 * secondary CPUs present.
 	 */
 	if (max_cpus == 0)
-		return;
+		goto out;
 
 	/*
 	 * Initialise the present map (which describes the set of CPUs
@@ -758,6 +775,8 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 		set_cpu_present(cpu, true);
 		numa_store_cpu_info(cpu);
 	}
+out:
+	__cpu_to_node = arm64_cpu_to_node;
 }
 
 static const char *ipi_types[NR_IPI] __tracepoint_string = {
-- 
2.40.1