x2apic_cluster.c

// SPDX-License-Identifier: GPL-2.0

#include <linux/cpuhotplug.h>
#include <linux/cpumask.h>
#include <linux/slab.h>
#include <linux/mm.h>

#include <asm/apic.h>

#include "local.h"

#define apic_cluster(apicid) ((apicid) >> 4)

/*
 * __x2apic_send_IPI_mask() possibly needs to read
 * x86_cpu_to_logical_apicid for all online cpus in a sequential way.
 * Using per cpu variable would cost one cache line per cpu.
 */
static u32 *x86_cpu_to_logical_apicid __read_mostly;

static DEFINE_PER_CPU(cpumask_var_t, ipi_mask);
static DEFINE_PER_CPU_READ_MOSTLY(struct cpumask *, cluster_masks);

static int x2apic_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
{
	return x2apic_enabled();
}

static void x2apic_send_IPI(int cpu, int vector)
{
	u32 dest = x86_cpu_to_logical_apicid[cpu];

	/* x2apic MSRs are special and need a special fence: */
	weak_wrmsr_fence();
	__x2apic_send_IPI_dest(dest, vector, APIC_DEST_LOGICAL);
}

static void
__x2apic_send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest)
{
	unsigned int cpu, clustercpu;
	struct cpumask *tmpmsk;
	unsigned long flags;
	u32 dest;

	/* x2apic MSRs are special and need a special fence: */
	weak_wrmsr_fence();
	local_irq_save(flags);

	tmpmsk = this_cpu_cpumask_var_ptr(ipi_mask);
	cpumask_copy(tmpmsk, mask);
	/* If IPI should not be sent to self, clear current CPU */
	if (apic_dest != APIC_DEST_ALLINC)
		__cpumask_clear_cpu(smp_processor_id(), tmpmsk);

	/* Collapse cpus in a cluster so a single IPI per cluster is sent */
	for_each_cpu(cpu, tmpmsk) {
		struct cpumask *cmsk = per_cpu(cluster_masks, cpu);

		dest = 0;
		for_each_cpu_and(clustercpu, tmpmsk, cmsk)
			dest |= x86_cpu_to_logical_apicid[clustercpu];

		if (!dest)
			continue;

		__x2apic_send_IPI_dest(dest, vector, APIC_DEST_LOGICAL);
		/* Remove cluster CPUs from tmpmask */
		cpumask_andnot(tmpmsk, tmpmsk, cmsk);
	}

	local_irq_restore(flags);
}

static void x2apic_send_IPI_mask(const struct cpumask *mask, int vector)
{
	__x2apic_send_IPI_mask(mask, vector, APIC_DEST_ALLINC);
}

static void
x2apic_send_IPI_mask_allbutself(const struct cpumask *mask, int vector)
{
	__x2apic_send_IPI_mask(mask, vector, APIC_DEST_ALLBUT);
}

static u32 x2apic_calc_apicid(unsigned int cpu)
{
	return x86_cpu_to_logical_apicid[cpu];
}

static void init_x2apic_ldr(void)
{
	struct cpumask *cmsk = this_cpu_read(cluster_masks);

	BUG_ON(!cmsk);

	cpumask_set_cpu(smp_processor_id(), cmsk);
}

/*
 * As an optimisation during boot, set the cluster_mask for all present
 * CPUs at once, to prevent each of them having to iterate over the others
 * to find the existing cluster_mask.
 */
static void prefill_clustermask(struct cpumask *cmsk, unsigned int cpu, u32 cluster)
{
	int cpu_i;

	for_each_present_cpu(cpu_i) {
		struct cpumask **cpu_cmsk = &per_cpu(cluster_masks, cpu_i);
		u32 apicid = apic->cpu_present_to_apicid(cpu_i);

		if (apicid == BAD_APICID || cpu_i == cpu || apic_cluster(apicid) != cluster)
			continue;

		if (WARN_ON_ONCE(*cpu_cmsk == cmsk))
			continue;

		BUG_ON(*cpu_cmsk);
		*cpu_cmsk = cmsk;
	}
}

static int alloc_clustermask(unsigned int cpu, u32 cluster, int node)
{
	struct cpumask *cmsk = NULL;
	unsigned int cpu_i;

	/*
	 * At boot time, the CPU present mask is stable. The cluster mask is
	 * allocated for the first CPU in the cluster and propagated to all
	 * present siblings in the cluster. If the cluster mask is already set
	 * on entry to this function for a given CPU, there is nothing to do.
	 */
	if (per_cpu(cluster_masks, cpu))
		return 0;

	if (system_state < SYSTEM_RUNNING)
		goto alloc;

	/*
	 * On post boot hotplug for a CPU which was not present at boot time,
	 * iterate over all possible CPUs (even those which are not present
	 * any more) to find any existing cluster mask.
	 */
	for_each_possible_cpu(cpu_i) {
		u32 apicid = apic->cpu_present_to_apicid(cpu_i);

		if (apicid != BAD_APICID && apic_cluster(apicid) == cluster) {
			cmsk = per_cpu(cluster_masks, cpu_i);
			/*
			 * If the cluster is already initialized, just store
			 * the mask and return. There's no need to propagate.
			 */
			if (cmsk) {
				per_cpu(cluster_masks, cpu) = cmsk;
				return 0;
			}
		}
	}
	/*
	 * No CPU in the cluster has ever been initialized, so fall through to
	 * the boot time code which will also populate the cluster mask for any
	 * other CPU in the cluster which is (now) present.
	 */
alloc:
	cmsk = kzalloc_node(sizeof(*cmsk), GFP_KERNEL, node);
	if (!cmsk)
		return -ENOMEM;
	per_cpu(cluster_masks, cpu) = cmsk;
	prefill_clustermask(cmsk, cpu, cluster);

	return 0;
}

static int x2apic_prepare_cpu(unsigned int cpu)
{
	u32 phys_apicid = apic->cpu_present_to_apicid(cpu);
	u32 cluster = apic_cluster(phys_apicid);
	u32 logical_apicid = (cluster << 16) | (1 << (phys_apicid & 0xf));
	int node = cpu_to_node(cpu);

	x86_cpu_to_logical_apicid[cpu] = logical_apicid;

	if (alloc_clustermask(cpu, cluster, node) < 0)
		return -ENOMEM;

	if (!zalloc_cpumask_var_node(&per_cpu(ipi_mask, cpu), GFP_KERNEL, node))
		return -ENOMEM;

	return 0;
}

static int x2apic_dead_cpu(unsigned int dead_cpu)
{
	struct cpumask *cmsk = per_cpu(cluster_masks, dead_cpu);

	if (cmsk)
		cpumask_clear_cpu(dead_cpu, cmsk);
	free_cpumask_var(per_cpu(ipi_mask, dead_cpu));
	return 0;
}

static int x2apic_cluster_probe(void)
{
	u32 slots;

	if (!x2apic_mode)
		return 0;

	slots = max_t(u32, L1_CACHE_BYTES/sizeof(u32), nr_cpu_ids);
	x86_cpu_to_logical_apicid = kcalloc(slots, sizeof(u32), GFP_KERNEL);
	if (!x86_cpu_to_logical_apicid)
		return 0;

	if (cpuhp_setup_state(CPUHP_X2APIC_PREPARE, "x86/x2apic:prepare",
			      x2apic_prepare_cpu, x2apic_dead_cpu) < 0) {
		pr_err("Failed to register X2APIC_PREPARE\n");
		kfree(x86_cpu_to_logical_apicid);
		x86_cpu_to_logical_apicid = NULL;
		return 0;
	}
	init_x2apic_ldr();
	return 1;
}

static struct apic apic_x2apic_cluster __ro_after_init = {

	.name				= "cluster x2apic",
	.probe				= x2apic_cluster_probe,
	.acpi_madt_oem_check		= x2apic_acpi_madt_oem_check,

	.dest_mode_logical		= true,

	.disable_esr			= 0,

	.init_apic_ldr			= init_x2apic_ldr,
	.cpu_present_to_apicid		= default_cpu_present_to_apicid,

	.max_apic_id			= UINT_MAX,
	.x2apic_set_max_apicid		= true,
	.get_apic_id			= x2apic_get_apic_id,

	.calc_dest_apicid		= x2apic_calc_apicid,

	.send_IPI			= x2apic_send_IPI,
	.send_IPI_mask			= x2apic_send_IPI_mask,
	.send_IPI_mask_allbutself	= x2apic_send_IPI_mask_allbutself,
	.send_IPI_allbutself		= x2apic_send_IPI_allbutself,
	.send_IPI_all			= x2apic_send_IPI_all,
	.send_IPI_self			= x2apic_send_IPI_self,
	.nmi_to_offline_cpu		= true,

	.read				= native_apic_msr_read,
	.write				= native_apic_msr_write,
	.eoi				= native_apic_msr_eoi,
	.icr_read			= native_x2apic_icr_read,
	.icr_write			= native_x2apic_icr_write,
};

apic_driver(apic_x2apic_cluster);