x86/cpu/topology: Assign hotpluggable CPUIDs during init

There is no point in assigning the CPU numbers during ACPI physical
hotplug. The number of possible hotplug CPUs is known when the possible map
is initialized, so the CPU numbers can be associated to the registered
non-present APIC IDs right there.

This allows to put more code into the __init section and makes the related
data __ro_after_init.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Link: https://lore.kernel.org/r/20240213210252.517339971@linutronix.de

diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
index a6d045b15ebdc066e1fd26ae009dbaf921532ccd..07124da9df717494d4aff994f6c7351fb18bd4aa 100644 (file)
--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -45,7 +45,7 @@ EXPORT_EARLY_PER_CPU_SYMBOL(x86_cpu_to_acpiid);
 DECLARE_BITMAP(phys_cpu_present_map, MAX_LOCAL_APIC) __read_mostly;
 
 /* Used for CPU number allocation and parallel CPU bringup */
-u32 cpuid_to_apicid[] __read_mostly = { [0 ... NR_CPUS - 1] = BAD_APICID, };
+u32 cpuid_to_apicid[] __ro_after_init = { [0 ... NR_CPUS - 1] = BAD_APICID, };
 
 /* Bitmaps to mark registered APICs at each topology domain */
 static struct { DECLARE_BITMAP(map, MAX_LOCAL_APIC); } apic_maps[TOPO_MAX_DOMAIN] __ro_after_init;
@@ -60,7 +60,7 @@ static struct {
        unsigned int            nr_rejected_cpus;
        u32                     boot_cpu_apic_id;
        u32                     real_bsp_apic_id;
-} topo_info __read_mostly = {
+} topo_info __ro_after_init = {
        .nr_assigned_cpus       = 1,
        .boot_cpu_apic_id       = BAD_APICID,
        .real_bsp_apic_id       = BAD_APICID,
@@ -133,7 +133,7 @@ static int topo_lookup_cpuid(u32 apic_id)
        return -ENODEV;
 }
 
-static int topo_get_cpunr(u32 apic_id)
+static __init int topo_get_cpunr(u32 apic_id)
 {
        int cpu = topo_lookup_cpuid(apic_id);
 
@@ -149,8 +149,6 @@ static void topo_set_cpuids(unsigned int cpu, u32 apic_id, u32 acpi_id)
        early_per_cpu(x86_cpu_to_apicid, cpu) = apic_id;
        early_per_cpu(x86_cpu_to_acpiid, cpu) = acpi_id;
 #endif
-       cpuid_to_apicid[cpu] = apic_id;
-
        set_cpu_possible(cpu, true);
        set_cpu_present(cpu, true);
 
@@ -206,6 +204,8 @@ static __init void topo_register_apic(u32 apic_id, u32 acpi_id, bool present)
                        cpu = 0;
                else
                        cpu = topo_get_cpunr(apic_id);
+
+               cpuid_to_apicid[cpu] = apic_id;
                topo_set_cpuids(cpu, apic_id, acpi_id);
        } else {
                topo_info.nr_disabled_cpus++;
@@ -277,12 +277,9 @@ int topology_hotplug_apic(u32 apic_id, u32 acpi_id)
                return -ENODEV;
 
        cpu = topo_lookup_cpuid(apic_id);
-       if (cpu < 0) {
-               if (topo_info.nr_assigned_cpus >= nr_cpu_ids)
-                       return -ENOSPC;
+       if (cpu < 0)
+               return -ENOSPC;
 
-               cpu = topo_assign_cpunr(apic_id);
-       }
        set_bit(apic_id, phys_cpu_present_map);
        topo_set_cpuids(cpu, apic_id, acpi_id);
        return cpu;
@@ -353,6 +350,7 @@ void __init topology_init_possible_cpus(void)
        unsigned int disabled = topo_info.nr_disabled_cpus;
        unsigned int total = assigned + disabled;
        unsigned int cpu, allowed = 1;
+       u32 apicid;
 
        if (!restrict_to_up()) {
                if (WARN_ON_ONCE(assigned > nr_cpu_ids)) {
@@ -381,8 +379,17 @@ void __init topology_init_possible_cpus(void)
        init_cpu_present(cpumask_of(0));
        init_cpu_possible(cpumask_of(0));
 
+       /* Assign CPU numbers to non-present CPUs */
+       for (apicid = 0; disabled; disabled--, apicid++) {
+               apicid = find_next_andnot_bit(apic_maps[TOPO_SMT_DOMAIN].map, phys_cpu_present_map,
+                                             MAX_LOCAL_APIC, apicid);
+               if (apicid >= MAX_LOCAL_APIC)
+                       break;
+               cpuid_to_apicid[topo_info.nr_assigned_cpus++] = apicid;
+       }
+
        for (cpu = 0; cpu < allowed; cpu++) {
-               u32 apicid = cpuid_to_apicid[cpu];
+               apicid = cpuid_to_apicid[cpu];
 
                set_cpu_possible(cpu, true);