path: root/arch/powerpc/platforms/pseries/hotplug-cpu.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * pseries CPU Hotplug infrastructure.
 *
 * Split out from arch/powerpc/platforms/pseries/setup.c
 *  arch/powerpc/kernel/rtas.c, and arch/powerpc/platforms/pseries/smp.c
 *
 * Peter Bergner, IBM	March 2001.
 * Copyright (C) 2001 IBM.
 * Dave Engebretsen, Peter Bergner, and
 * Mike Corrigan {engebret|bergner|mikec}@us.ibm.com
 * Plus various changes from other IBM teams...
 *
 * Copyright (C) 2006 Michael Ellerman, IBM Corporation
 */

#define pr_fmt(fmt)     "pseries-hotplug-cpu: " fmt

#include <linux/kernel.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
#include <linux/sched.h>	/* for idle_task_exit */
#include <linux/sched/hotplug.h>
#include <linux/cpu.h>
#include <linux/of.h>
#include <linux/slab.h>
#include <asm/prom.h>
#include <asm/rtas.h>
#include <asm/firmware.h>
#include <asm/machdep.h>
#include <asm/vdso_datapage.h>
#include <asm/xics.h>
#include <asm/xive.h>
#include <asm/plpar_wrappers.h>
#include <asm/topology.h>

#include "pseries.h"

/* This version can't take the spinlock, because it never returns */
static int rtas_stop_self_token = RTAS_UNKNOWN_SERVICE;

/*
 * Record the CPU ids used on each nodes.
 * Protected by cpu_add_remove_lock.
 */
static cpumask_var_t node_recorded_ids_map[MAX_NUMNODES];

static void rtas_stop_self(void)
{
	static struct rtas_args args;

	local_irq_disable();

	BUG_ON(rtas_stop_self_token == RTAS_UNKNOWN_SERVICE);

	rtas_call_unlocked(&args, rtas_stop_self_token, 0, 1, NULL);

	panic("Alas, I survived.\n");
}

static void pseries_cpu_offline_self(void)
{
	unsigned int hwcpu = hard_smp_processor_id();

	local_irq_disable();
	idle_task_exit();
	if (xive_enabled())
		xive_teardown_cpu();
	else
		xics_teardown_cpu();

	unregister_slb_shadow(hwcpu);
	rtas_stop_self();

	/* Should never get here... */
	BUG();
	for(;;);
}

static int pseries_cpu_disable(void)
{
	int cpu = smp_processor_id();

	set_cpu_online(cpu, false);
	vdso_data->processorCount--;

	/*fix boot_cpuid here*/
	if (cpu == boot_cpuid)
		boot_cpuid = cpumask_any(cpu_online_mask);

	/* FIXME: abstract this to not be platform specific later on */
	if (xive_enabled())
		xive_smp_disable_cpu();
	else
		xics_migrate_irqs_away();

	cleanup_cpu_mmu_context();

	return 0;
}

/*
 * pseries_cpu_die: Wait for the cpu to die.
 * @cpu: logical processor id of the CPU whose death we're awaiting.
 *
 * This function is called from the context of the thread which is performing
 * the cpu-offline. Here we wait for long enough to allow the cpu in question
 * to self-destroy so that the cpu-offline thread can send the CPU_DEAD
 * notifications.
 *
 * OTOH, pseries_cpu_offline_self() is called by the @cpu when it wants to
 * self-destruct.
 */
static void pseries_cpu_die(unsigned int cpu)
{
	int cpu_status = 1;
	unsigned int pcpu = get_hard_smp_processor_id(cpu);
	unsigned long timeout = jiffies + msecs_to_jiffies(120000);

	while (true) {
		cpu_status = smp_query_cpu_stopped(pcpu);
		if (cpu_status == QCSS_STOPPED ||
		    cpu_status == QCSS_HARDWARE_ERROR)
			break;

		if (time_after(jiffies, timeout)) {
			pr_warn("CPU %i (hwid %i) didn't die after 120 seconds\n",
				cpu, pcpu);
			timeout = jiffies + msecs_to_jiffies(120000);
		}

		cond_resched();
	}

	if (cpu_status == QCSS_HARDWARE_ERROR) {
		pr_warn("CPU %i (hwid %i) reported error while dying\n",
			cpu, pcpu);
	}

	paca_ptrs[cpu]->cpu_start = 0;
}

/**
 * find_cpu_id_range - found a linear ranger of @nthreads free CPU ids.
 * @nthreads : the number of threads (cpu ids)
 * @assigned_node : the node it belongs to or NUMA_NO_NODE if free ids from any
 *                  node can be peek.
 * @cpu_mask: the returned CPU mask.
 *
 * Returns 0 on success.
 */
static int find_cpu_id_range(unsigned int nthreads, int assigned_node,
			     cpumask_var_t *cpu_mask)
{
	cpumask_var_t candidate_mask;
	unsigned int cpu, node;
	int rc = -ENOSPC;

	if (!zalloc_cpumask_var(&candidate_mask, GFP_KERNEL))
		return -ENOMEM;

	cpumask_clear(*cpu_mask);
	for (cpu = 0; cpu < nthreads; cpu++)
		cpumask_set_cpu(cpu, *cpu_mask);

	BUG_ON(!cpumask_subset(cpu_present_mask, cpu_possible_mask));

	/* Get a bitmap of unoccupied slots. */
	cpumask_xor(candidate_mask, cpu_possible_mask, cpu_present_mask);

	if (assigned_node != NUMA_NO_NODE) {
		/*
		 * Remove free ids previously assigned on the other nodes. We
		 * can walk only online nodes because once a node became online
		 * it is not turned offlined back.
		 */
		for_each_online_node(node) {
			if (node == assigned_node)
				continue;
			cpumask_andnot(candidate_mask, candidate_mask,
				       node_recorded_ids_map[node]);
		}
	}

	if (cpumask_empty(candidate_mask))
		goto out;

	while (!cpumask_empty(*cpu_mask)) {
		if (cpumask_subset(*cpu_mask, candidate_mask))
			/* Found a range where we can insert the new cpu(s) */
			break;
		cpumask_shift_left(*cpu_mask, *cpu_mask, nthreads);
	}

	if (!cpumask_empty(*cpu_mask))
		rc = 0;

out:
	free_cpumask_var(candidate_mask);
	return rc;
}

/*
 * Update cpu_present_mask and paca(s) for a new cpu node.  The wrinkle
 * here is that a cpu device node may represent multiple logical cpus
 * in the SMT case.  We must honor the assumption in other code that
 * the logical ids for sibling SMT threads x and y are adjacent, such
 * that x^1 == y and y^1 == x.
 */
static int pseries_add_processor(struct device_node *np)
{
	int len, nthreads, node, cpu, assigned_node;
	int rc = 0;
	cpumask_var_t cpu_mask;
	const __be32 *intserv;

	intserv = of_get_property(np, "ibm,ppc-interrupt-server#s", &len);
	if (!intserv)
		return 0;

	nthreads = len / sizeof(u32);

	if (!alloc_cpumask_var(&cpu_mask, GFP_KERNEL))
		return -ENOMEM;

	/*
	 * Fetch from the DT nodes read by dlpar_configure_connector() the NUMA
	 * node id the added CPU belongs to.
	 */
	node = of_node_to_nid(np);
	if (node < 0 || !node_possible(node))
		node = first_online_node;

	BUG_ON(node == NUMA_NO_NODE);
	assigned_node = node;

	cpu_maps_update_begin();

	rc = find_cpu_id_range(nthreads, node, &cpu_mask);
	if (rc && nr_node_ids > 1) {
		/*
		 * Try again, considering the free CPU ids from the other node.
		 */
		node = NUMA_NO_NODE;
		rc = find_cpu_id_range(nthreads, NUMA_NO_NODE, &cpu_mask);
	}

	if (rc) {
		pr_err("Cannot add cpu %pOF; this system configuration"
		       " supports %d logical cpus.\n", np, num_possible_cpus());
		goto out;
	}

	for_each_cpu(cpu, cpu_mask) {
		BUG_ON(cpu_present(cpu));
		set_cpu_present(cpu, true);
		set_hard_smp_processor_id(cpu, be32_to_cpu(*intserv++));
	}

	/* Record the newly used CPU ids for the associate node. */
	cpumask_or(node_recorded_ids_map[assigned_node],
		   node_recorded_ids_map[assigned_node], cpu_mask);

	/*
	 * If node is set to NUMA_NO_NODE, CPU ids have be reused from
	 * another node, remove them from its mask.
	 */
	if (node == NUMA_NO_NODE) {
		cpu = cpumask_first(cpu_mask);
		pr_warn("Reusing free CPU ids %d-%d from another node\n",
			cpu, cpu + nthreads - 1);
		for_each_online_node(node) {
			if (node == assigned_node)
				continue;
			cpumask_andnot(node_recorded_ids_map[node],
				       node_recorded_ids_map[node],
				       cpu_mask);
		}
	}

out:
	cpu_maps_update_done();
	free_cpumask_var(cpu_mask);
	return rc;
}

/*
 * Update the present map for a cpu node which is going away, and set
 * the hard id in the paca(s) to -1 to be consistent with boot time
 * convention for non-present cpus.
 */
static void pseries_remove_processor(struct device_node *np)
{
	unsigned int cpu;
	int len, nthreads, i;
	const __be32 *intserv;
	u32 thread;

	intserv = of_get_property(np, "ibm,ppc-interrupt-server#s", &len);
	if (!intserv)
		return;

	nthreads = len / sizeof(u32);

	cpu_maps_update_begin();
	for (i = 0; i < nthreads; i++) {
		thread = be32_to_cpu(intserv[i]);
		for_each_present_cpu(cpu) {
			if (get_hard_smp_processor_id(cpu) != thread)
				continue;
			BUG_ON(cpu_online(cpu));
			set_cpu_present(cpu, false);
			set_hard_smp_processor_id(cpu, -1);
			update_numa_cpu_lookup_table(cpu, -1);
			break;
		}
		if (cpu >= nr_cpu_ids)
			printk(KERN_WARNING "Could not find cpu to remove "
			       "with physical id 0x%x\n", thread);
	}
	cpu_maps_update_done();
}

static int dlpar_offline_cpu(struct device_node *dn)
{
	int rc = 0;
	unsigned int cpu;
	int len, nthreads, i;
	const __be32 *intserv;
	u32 thread;

	intserv = of_get_property(dn, "ibm,ppc-interrupt-server#s", &len);
	if (!intserv)
		return -EINVAL;

	nthreads = len / sizeof(u32);

	cpu_maps_update_begin();
	for (i = 0; i < nthreads; i++) {
		thread = be32_to_cpu(intserv[i]);
		for_each_present_cpu(cpu) {
			if (get_hard_smp_processor_id(cpu) != thread)
				continue;

			if (!cpu_online(cpu))
				break;

			/*
			 * device_offline() will return -EBUSY (via cpu_down()) if there
			 * is only one CPU left. Check it here to fail earlier and with a
			 * more informative error message, while also retaining the
			 * cpu_add_remove_lock to be sure that no CPUs are being
			 * online/offlined during this check.
			 */
			if (num_online_cpus() == 1) {
				pr_warn("Unable to remove last online CPU %pOFn\n", dn);
				rc = -EBUSY;
				goto out_unlock;
			}

			cpu_maps_update_done();
			rc = device_offline(get_cpu_device(cpu));
			if (rc)
				goto out;
			cpu_maps_update_begin();
			break;
		}
		if (cpu == num_possible_cpus()) {
			pr_warn("Could not find cpu to offline with physical id 0x%x\n",
				thread);
		}
	}
out_unlock:
	cpu_maps_update_done();

out:
	return rc;
}

static int dlpar_online_cpu(struct device_node *dn)
{
	int rc = 0;
	unsigned int cpu;
	int len, nthreads, i;
	const __be32 *intserv;
	u32 thread;

	intserv = of_get_property(dn, "ibm,ppc-interrupt-server#s", &len);
	if (!intserv)
		return -EINVAL;

	nthreads = len / sizeof(u32);

	cpu_maps_update_begin();
	for (i = 0; i < nthreads; i++) {
		thread = be32_to_cpu(intserv[i]);
		for_each_present_cpu(cpu) {
			if (get_hard_smp_processor_id(cpu) != thread)
				continue;
			cpu_maps_update_done();
			find_and_update_cpu_nid(cpu);
			rc = device_online(get_cpu_device(cpu));
			if (rc) {
				dlpar_offline_cpu(dn);
				goto out;
			}
			cpu_maps_update_begin();

			break;
		}
		if (cpu == num_possible_cpus())
			printk(KERN_WARNING "Could not find cpu to online "
			       "with physical id 0x%x\n", thread);
	}
	cpu_maps_update_done();

out:
	return rc;

}

static bool dlpar_cpu_exists(struct device_node *parent, u32 drc_index)
{
	struct device_node *child = NULL;
	u32 my_drc_index;
	bool found;
	int rc;

	/* Assume cpu doesn't exist */
	found = false;

	for_each_child_of_node(parent, child) {
		rc = of_property_read_u32(child, "ibm,my-drc-index",
					  &my_drc_index);
		if (rc)
			continue;

		if (my_drc_index == drc_index) {
			of_node_put(child);
			found = true;
			break;
		}
	}

	return found;
}

static bool drc_info_valid_index(struct device_node *parent, u32 drc_index)
{
	struct property *info;
	struct of_drc_info drc;
	const __be32 *value;
	u32 index;
	int count, i, j;

	info = of_find_property(parent, "ibm,drc-info", NULL);
	if (!info)
		return false;

	value = of_prop_next_u32(info, NULL, &count);

	/* First value of ibm,drc-info is number of drc-info records */
	if (value)
		value++;
	else
		return false;

	for (i = 0; i < count; i++) {
		if (of_read_drc_info_cell(&info, &value, &drc))
			return false;

		if (strncmp(drc.drc_type, "CPU", 3))
			break;

		if (drc_index > drc.last_drc_index)
			continue;

		index = drc.drc_index_start;
		for (j = 0; j < drc.num_sequential_elems; j++) {
			if (drc_index == index)
				return true;

			index += drc.sequential_inc;
		}
	}

	return false;
}

static bool valid_cpu_drc_index(struct device_node *parent, u32 drc_index)
{
	bool found = false;
	int rc, index;

	if (of_find_property(parent, "ibm,drc-info", NULL))
		return drc_info_valid_index(parent, drc_index);

	/* Note that the format of the ibm,drc-indexes array is
	 * the number of entries in the array followed by the array
	 * of drc values so we start looking at index = 1.
	 */
	index = 1;
	while (!found) {
		u32 drc;

		rc = of_property_read_u32_index(parent, "ibm,drc-indexes",
						index++, &drc);

		if (rc)
			break;

		if (drc == drc_index)
			found = true;
	}

	return found;
}

static int pseries_cpuhp_attach_nodes(struct device_node *dn)
{
	struct of_changeset cs;
	int ret;

	/*
	 * This device node is unattached but may have siblings; open-code the
	 * traversal.
	 */
	for (of_changeset_init(&cs); dn != NULL; dn = dn->sibling) {
		ret = of_changeset_attach_node(&cs, dn);
		if (ret)
			goto out;
	}

	ret = of_changeset_apply(&cs);
out:
	of_changeset_destroy(&cs);
	return ret;
}

static ssize_t dlpar_cpu_add(u32 drc_index)
{
	struct device_node *dn, *parent;
	int rc, saved_rc;

	pr_debug("Attempting to add CPU, drc index: %x\n", drc_index);

	parent = of_find_node_by_path("/cpus");
	if (!parent) {
		pr_warn("Failed to find CPU root node \"/cpus\"\n");
		return -ENODEV;
	}

	if (dlpar_cpu_exists(parent, drc_index)) {
		of_node_put(parent);
		pr_warn("CPU with drc index %x already exists\n", drc_index);
		return -EINVAL;
	}

	if (!valid_cpu_drc_index(parent, drc_index)) {
		of_node_put(parent);
		pr_warn("Cannot find CPU (drc index %x) to add.\n", drc_index);
		return -EINVAL;
	}

	rc = dlpar_acquire_drc(drc_index);
	if (rc) {
		pr_warn("Failed to acquire DRC, rc: %d, drc index: %x\n",
			rc, drc_index);
		of_node_put(parent);
		return -EINVAL;
	}

	dn = dlpar_configure_connector(cpu_to_be32(drc_index), parent);
	if (!dn) {
		pr_warn("Failed call to configure-connector, drc index: %x\n",
			drc_index);
		dlpar_release_drc(drc_index);
		of_node_put(parent);
		return -EINVAL;
	}

	rc = pseries_cpuhp_attach_nodes(dn);

	/* Regardless we are done with parent now */
	of_node_put(parent);

	if (rc) {
		saved_rc = rc;
		pr_warn("Failed to attach node %pOFn, rc: %d, drc index: %x\n",
			dn, rc, drc_index);

		rc = dlpar_release_drc(drc_index);
		if (!rc)
			dlpar_free_cc_nodes(dn);

		return saved_rc;
	}

	update_numa_distance(dn);

	rc = dlpar_online_cpu(dn);
	if (rc) {
		saved_rc = rc;
		pr_warn("Failed to online cpu %pOFn, rc: %d, drc index: %x\n",
			dn, rc, drc_index);

		rc = dlpar_detach_node(dn);
		if (!rc)
			dlpar_release_drc(drc_index);

		return saved_rc;
	}

	pr_debug("Successfully added CPU %pOFn, drc index: %x\n", dn,
		 drc_index);
	return rc;
}

static unsigned int pseries_cpuhp_cache_use_count(const struct device_node *cachedn)
{
	unsigned int use_count = 0;
	struct device_node *dn, *tn;

	WARN_ON(!of_node_is_type(cachedn, "cache"));

	for_each_of_cpu_node(dn) {
		tn = of_find_next_cache_node(dn);
		of_node_put(tn);
		if (tn == cachedn)
			use_count++;
	}

	for_each_node_by_type(dn, "cache") {
		tn = of_find_next_cache_node(dn);
		of_node_put(tn);
		if (tn == cachedn)
			use_count++;
	}

	return use_count;
}

static int pseries_cpuhp_detach_nodes(struct device_node *cpudn)
{
	struct device_node *dn;
	struct of_changeset cs;
	int ret = 0;

	of_changeset_init(&cs);
	ret = of_changeset_detach_node(&cs, cpudn);
	if (ret)
		goto out;

	dn = cpudn;
	while ((dn = of_find_next_cache_node(dn))) {
		if (pseries_cpuhp_cache_use_count(dn) > 1) {
			of_node_put(dn);
			break;
		}

		ret = of_changeset_detach_node(&cs, dn);
		of_node_put(dn);
		if (ret)
			goto out;
	}

	ret = of_changeset_apply(&cs);
out:
	of_changeset_destroy(&cs);
	return ret;
}

static ssize_t dlpar_cpu_remove(struct device_node *dn, u32 drc_index)
{
	int rc;

	pr_debug("Attempting to remove CPU %pOFn, drc index: %x\n",
		 dn, drc_index);

	rc = dlpar_offline_cpu(dn);
	if (rc) {
		pr_warn("Failed to offline CPU %pOFn, rc: %d\n", dn, rc);
		return -EINVAL;
	}

	rc = dlpar_release_drc(drc_index);
	if (rc) {
		pr_warn("Failed to release drc (%x) for CPU %pOFn, rc: %d\n",
			drc_index, dn, rc);
		dlpar_online_cpu(dn);
		return rc;
	}

	rc = pseries_cpuhp_detach_nodes(dn);
	if (rc) {
		int saved_rc = rc;

		pr_warn("Failed to detach CPU %pOFn, rc: %d", dn, rc);

		rc = dlpar_acquire_drc(drc_index);
		if (!rc)
			dlpar_online_cpu(dn);

		return saved_rc;
	}

	pr_debug("Successfully removed CPU, drc index: %x\n", drc_index);
	return 0;
}

static struct device_node *cpu_drc_index_to_dn(u32 drc_index)
{
	struct device_node *dn;
	u32 my_index;
	int rc;

	for_each_node_by_type(dn, "cpu") {
		rc = of_property_read_u32(dn, "ibm,my-drc-index", &my_index);
		if (rc)
			continue;

		if (my_index == drc_index)
			break;
	}

	return dn;
}

static int dlpar_cpu_remove_by_index(u32 drc_index)
{
	struct device_node *dn;
	int rc;

	dn = cpu_drc_index_to_dn(drc_index);
	if (!dn) {
		pr_warn("Cannot find CPU (drc index %x) to remove\n",
			drc_index);
		return -ENODEV;
	}

	rc = dlpar_cpu_remove(dn, drc_index);
	of_node_put(dn);
	return rc;
}

int dlpar_cpu(struct pseries_hp_errorlog *hp_elog)
{
	u32 drc_index;
	int rc;

	drc_index = hp_elog->_drc_u.drc_index;

	lock_device_hotplug();

	switch (hp_elog->action) {
	case PSERIES_HP_ELOG_ACTION_REMOVE:
		if (hp_elog->id_type == PSERIES_HP_ELOG_ID_DRC_INDEX) {
			rc = dlpar_cpu_remove_by_index(drc_index);
			/*
			 * Setting the isolation state of an UNISOLATED/CONFIGURED
			 * device to UNISOLATE is a no-op, but the hypervisor can
			 * use it as a hint that the CPU removal failed.
			 */
			if (rc)
				dlpar_unisolate_drc(drc_index);
		}
		else
			rc = -EINVAL;
		break;
	case PSERIES_HP_ELOG_ACTION_ADD:
		if (hp_elog->id_type == PSERIES_HP_ELOG_ID_DRC_INDEX)
			rc = dlpar_cpu_add(drc_index);
		else
			rc = -EINVAL;
		break;
	default:
		pr_err("Invalid action (%d) specified\n", hp_elog->action);
		rc = -EINVAL;
		break;
	}

	unlock_device_hotplug();
	return rc;
}

#ifdef CONFIG_ARCH_CPU_PROBE_RELEASE

static ssize_t dlpar_cpu_probe(const char *buf, size_t count)
{
	u32 drc_index;
	int rc;

	rc = kstrtou32(buf, 0, &drc_index);
	if (rc)
		return -EINVAL;

	rc = dlpar_cpu_add(drc_index);

	return rc ? rc : count;
}

static ssize_t dlpar_cpu_release(const char *buf, size_t count)
{
	struct device_node *dn;
	u32 drc_index;
	int rc;

	dn = of_find_node_by_path(buf);
	if (!dn)
		return -EINVAL;

	rc = of_property_read_u32(dn, "ibm,my-drc-index", &drc_index);
	if (rc) {
		of_node_put(dn);
		return -EINVAL;
	}

	rc = dlpar_cpu_remove(dn, drc_index);
	of_node_put(dn);

	return rc ? rc : count;
}

#endif /* CONFIG_ARCH_CPU_PROBE_RELEASE */

static int pseries_smp_notifier(struct notifier_block *nb,
				unsigned long action, void *data)
{
	struct of_reconfig_data *rd = data;
	int err = 0;

	switch (action) {
	case OF_RECONFIG_ATTACH_NODE:
		err = pseries_add_processor(rd->dn);
		break;
	case OF_RECONFIG_DETACH_NODE:
		pseries_remove_processor(rd->dn);
		break;
	}
	return notifier_from_errno(err);
}

static struct notifier_block pseries_smp_nb = {
	.notifier_call = pseries_smp_notifier,
};

static int __init pseries_cpu_hotplug_init(void)
{
	int qcss_tok;
	unsigned int node;

#ifdef CONFIG_ARCH_CPU_PROBE_RELEASE
	ppc_md.cpu_probe = dlpar_cpu_probe;
	ppc_md.cpu_release = dlpar_cpu_release;
#endif /* CONFIG_ARCH_CPU_PROBE_RELEASE */

	rtas_stop_self_token = rtas_token("stop-self");
	qcss_tok = rtas_token("query-cpu-stopped-state");

	if (rtas_stop_self_token == RTAS_UNKNOWN_SERVICE ||
			qcss_tok == RTAS_UNKNOWN_SERVICE) {
		printk(KERN_INFO "CPU Hotplug not supported by firmware "
				"- disabling.\n");
		return 0;
	}

	smp_ops->cpu_offline_self = pseries_cpu_offline_self;
	smp_ops->cpu_disable = pseries_cpu_disable;
	smp_ops->cpu_die = pseries_cpu_die;

	/* Processors can be added/removed only on LPAR */
	if (firmware_has_feature(FW_FEATURE_LPAR)) {
		for_each_node(node) {
			if (!alloc_cpumask_var_node(&node_recorded_ids_map[node],
						    GFP_KERNEL, node))
				return -ENOMEM;

			/* Record ids of CPU added at boot time */
			cpumask_copy(node_recorded_ids_map[node],
				     cpumask_of_node(node));
		}

		of_reconfig_notifier_register(&pseries_smp_nb);
	}

	return 0;
}
machine_arch_initcall(pseries, pseries_cpu_hotplug_init);