[patch 36/53] x86/cpu/topology: Rework possible CPU management

Thomas Gleixner
2023-08-07T13:54:57Z

Managing possible CPUs is an unreadable and uncomprehensible maze. Aside of
that it's backwards because it applies command line limits after
registering all APICs.

Rewrite it so that it:

- Applies the command line limits upfront so that only the allowed amount
of APIC IDs can be registered.

- Applies eventual late restrictions in an understandable way

- Uses simple min_t() calculations which are trivial to follow.

- Provides a separate function for resetting to UP mode late in the
bringup process.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/include/asm/apic.h | 5 +
arch/x86/include/asm/topology.h | 4
arch/x86/kernel/cpu/topology.c | 176 ++++++++++++++++++++++++----------------
arch/x86/kernel/setup.c | 9 --
arch/x86/kernel/smpboot.c | 6 -
5 files changed, 120 insertions(+), 80 deletions(-)

--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -175,6 +175,9 @@ extern void topology_register_apic(u32 a
extern void topology_register_boot_apic(u32 apic_id);
extern int topology_hotplug_apic(u32 apic_id, u32 acpi_id);
extern void topology_hotunplug_apic(unsigned int cpu);
+extern void topology_apply_cmdline_limits_early(void);
+extern void topology_init_possible_cpus(void);
+extern void topology_reset_possible_cpus_up(void);

#else /* !CONFIG_X86_LOCAL_APIC */
static inline void lapic_shutdown(void) { }
@@ -190,6 +193,8 @@ static inline void apic_intr_mode_init(v
static inline void lapic_assign_system_vectors(void) { }
static inline void lapic_assign_legacy_vector(unsigned int i, bool r) { }
static inline bool apic_needs_pit(void) { return true; }
+static inline void topology_apply_cmdline_limits_early(void) { }
+static inline void topology_init_possible_cpus(void) { }
#endif /* !CONFIG_X86_LOCAL_APIC */

#ifdef CONFIG_X86_X2APIC
--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -190,6 +190,9 @@ static inline bool topology_is_primary_t
{
return cpumask_test_cpu(cpu, cpu_primary_thread_mask);
}
+
+void topology_apply_cmdline_limits_early(void);
+
#else /* CONFIG_SMP */
#define topology_max_packages() (1)
static inline int
@@ -202,6 +205,7 @@ static inline int topology_max_smt_threa
static inline bool topology_is_primary_thread(unsigned int cpu) { return true; }
static inline bool topology_smt_supported(void) { return false; }
static inline unsigned int topology_amd_nodes_per_pkg(void) { return 0; };
+static inline void topology_apply_cmdline_limits_early(void) { }
#endif /* !CONFIG_SMP */

static inline void arch_fix_phys_package_id(int num, u32 slot)
--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -5,6 +5,7 @@
#include <xen/xen.h>

#include <asm/apic.h>
+#include <asm/io_apic.h>
#include <asm/mpspec.h>
#include <asm/smp.h>

@@ -85,73 +86,6 @@ early_initcall(smp_init_primary_thread_m
static inline void cpu_mark_primary_thread(unsigned int cpu, unsigned int apicid) { }
#endif

-static int __initdata setup_possible_cpus = -1;
-
-/*
- * cpu_possible_mask should be static, it cannot change as cpu's
- * are onlined, or offlined. The reason is per-cpu data-structures
- * are allocated by some modules at init time, and don't expect to
- * do this dynamically on cpu arrival/departure.
- * cpu_present_mask on the other hand can change dynamically.
- * In case when cpu_hotplug is not compiled, then we resort to current
- * behaviour, which is cpu_possible == cpu_present.
- * - Ashok Raj
- *
- * Three ways to find out the number of additional hotplug CPUs:
- * - If the BIOS specified disabled CPUs in ACPI/mptables use that.
- * - The user can overwrite it with possible_cpus=NUM
- * - Otherwise don't reserve additional CPUs.
- * We do this because additional CPUs waste a lot of memory.
- * -AK
- */
-__init void prefill_possible_map(void)
-{
- unsigned int num_processors = topo_info.nr_assigned_cpus;
- unsigned int disabled_cpus = topo_info.nr_disabled_cpus;
- int i, possible;
-
- i = setup_max_cpus ?: 1;
- if (setup_possible_cpus == -1) {
- possible = topo_info.nr_assigned_cpus;
-#ifdef CONFIG_HOTPLUG_CPU
- if (setup_max_cpus)
- possible += num_processors;
-#else
- if (possible > i)
- possible = i;
-#endif
- } else
- possible = setup_possible_cpus;
-
- total_cpus = max_t(int, possible, num_processors + disabled_cpus);
-
- /* nr_cpu_ids could be reduced via nr_cpus= */
- if (possible > nr_cpu_ids) {
- pr_warn("%d Processors exceeds NR_CPUS limit of %u\n",
- possible, nr_cpu_ids);
- possible = nr_cpu_ids;
- }
-
-#ifdef CONFIG_HOTPLUG_CPU
- if (!setup_max_cpus)
-#endif
- if (possible > i) {
- pr_warn("%d Processors exceeds max_cpus limit of %u\n",
- possible, setup_max_cpus);
- possible = i;
- }
-
- set_nr_cpu_ids(possible);
-
- pr_info("Allowing %d CPUs, %d hotplug CPUs\n",
- possible, max_t(int, possible - num_processors, 0));
-
- reset_cpu_possible_mask();
-
- for (i = 0; i < possible; i++)
- set_cpu_possible(i, true);
-}
-
static int topo_lookup_cpuid(u32 apic_id)
{
int i;
@@ -294,12 +228,114 @@ void topology_hotunplug_apic(unsigned in
}
#endif

-static int __init _setup_possible_cpus(char *str)
+#ifdef CONFIG_SMP
+static unsigned int max_possible_cpus __initdata = NR_CPUS;
+
+/**
+ * topology_apply_cmdline_limits_early - Apply topology command line limits early
+ *
+ * Ensure that command line limits are in effect before firmware parsing
+ * takes place.
+ */
+void __init topology_apply_cmdline_limits_early(void)
+{
+ unsigned int possible = nr_cpu_ids;
+
+ /* 'maxcpus=0' 'nosmp' 'nolapic' 'disableapic' 'noapic' */
+ if (!setup_max_cpus || ioapic_is_disabled || apic_is_disabled)
+ possible = 1;
+
+ /* 'possible_cpus=N' */
+ possible = min_t(unsigned int, max_possible_cpus, possible);
+
+ if (possible < nr_cpu_ids) {
+ pr_info("Limiting to %u possible CPUs\n", possible);
+ set_nr_cpu_ids(possible);
+ }
+}
+
+static __init bool restrict_to_up(void)
+{
+ if (!smp_found_config || ioapic_is_disabled)
+ return true;
+ /*
+ * XEN PV is special as it does not advertise the local APIC
+ * properly, but provides a fake topology for it so that the
+ * infrastructure works. So don't apply the restrictions vs. APIC
+ * here.
+ */
+ if (xen_pv_domain())
+ return false;
+
+ return apic_is_disabled;
+}
+
+void __init topology_init_possible_cpus(void)
+{
+ unsigned int assigned = topo_info.nr_assigned_cpus;
+ unsigned int disabled = topo_info.nr_disabled_cpus;
+ unsigned int total = assigned + disabled;
+ unsigned int cpu, allowed = 1;
+
+ if (!restrict_to_up()) {
+ if (WARN_ON_ONCE(assigned > nr_cpu_ids)) {
+ disabled += assigned - nr_cpu_ids;
+ assigned = nr_cpu_ids;
+ }
+ allowed = min_t(unsigned int, total, nr_cpu_ids);
+ }
+
+ if (total > allowed)
+ pr_warn("%u possible CPUs exceed the limit of %u\n", total, allowed);
+
+ assigned = min_t(unsigned int, allowed, assigned);
+ disabled = allowed - assigned;
+
+ topo_info.nr_assigned_cpus = assigned;
+ topo_info.nr_disabled_cpus = disabled;
+
+ total_cpus = allowed;
+ set_nr_cpu_ids(allowed);
+
+ pr_info("Allowing %u present CPUs plus %u hotplug CPUs\n", assigned, disabled);
+ if (topo_info.nr_rejected_cpus)
+ pr_info("Rejected CPUs %u\n", topo_info.nr_rejected_cpus);
+
+ init_cpu_present(cpumask_of(0));
+ init_cpu_possible(cpumask_of(0));
+
+ for (cpu = 0; cpu < allowed; cpu++) {
+ u32 apicid = cpuid_to_apicid[cpu];
+
+ set_cpu_possible(cpu, true);
+
+ if (apicid == BAD_APICID)
+ continue;
+
+ set_cpu_present(cpu, test_bit(apicid, phys_cpu_present_map));
+ }
+}
+
+/*
+ * Late SMP disable after sizing CPU masks when APIC/IOAPIC setup failed.
+ */
+void __init topology_reset_possible_cpus_up(void)
{
- get_option(&str, &setup_possible_cpus);
+ init_cpu_present(cpumask_of(0));
+ init_cpu_possible(cpumask_of(0));
+
+ bitmap_zero(phys_cpu_present_map, MAX_LOCAL_APIC);
+ if (topo_info.boot_cpu_apic_id != BAD_APICID)
+ set_bit(topo_info.boot_cpu_apic_id, phys_cpu_present_map);
+}
+
+static int __init setup_possible_cpus(char *str)
+{
+ get_option(&str, &max_possible_cpus);
return 0;
}
-early_param("possible_cpus", _setup_possible_cpus);
+early_param("possible_cpus", setup_possible_cpus);
+#endif

static int __init apic_set_disabled_cpu_apicid(char *arg)
{
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1258,6 +1258,8 @@ void __init setup_arch(char **cmdline_p)

early_quirks();

+ topology_apply_cmdline_limits_early();
+
/*
* Parse SMP configuration. Try ACPI first and then the platform
* specific parser.
@@ -1265,13 +1267,10 @@ void __init setup_arch(char **cmdline_p)
acpi_boot_init();
x86_init.mpparse.parse_smp_cfg();

- /*
- * Systems w/o ACPI and mptables might not have it mapped the local
- * APIC yet, but prefill_possible_map() might need to access it.
- */
+ /* Last opportunity to detect and map the local APIC */
init_apic_mappings();

- prefill_possible_map();
+ topology_init_possible_cpus();

init_cpu_to_node();
init_gi_nodes();
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1156,11 +1156,7 @@ static __init void disable_smp(void)
pr_info("SMP disabled\n");

disable_ioapic_support();
-
- init_cpu_present(cpumask_of(0));
- init_cpu_possible(cpumask_of(0));
-
- reset_phys_cpu_present_map(smp_found_config ? boot_cpu_physical_apicid : 0);
+ topology_reset_possible_cpus_up();

cpumask_set_cpu(0, topology_sibling_cpumask(0));
cpumask_set_cpu(0, topology_core_cpumask(0));