cpumask: Add enabled cpumask for present CPUs that can be brought online

The 'offline' file in sysfs shows all offline CPUs, including those
that aren't present. User-space is expected to remove not-present CPUs
from this list to learn which CPUs could be brought online.

CPUs can be present but not-enabled. These CPUs can't be brought online
until the firmware policy changes, which comes with an ACPI notification
that will register the CPUs.

With only the offline and present files, user-space is unable to
determine which CPUs it can try to bring online. Add a new CPU mask
that shows this based on all the registered CPUs.

Signed-off-by: James Morse <james.morse@arm.com>
Tested-by: Miguel Luis <miguel.luis@oracle.com>
Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
Tested-by: Jianyong Wu <jianyong.wu@arm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20240529133446.28446-20-Jonathan.Cameron@huawei.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index e7e160954e798e50ecd5bea999b03e31bf280d7f..53ed1a803422d58c6cd1e5f557b8286c52418db1 100644 (file)
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -694,3 +694,9 @@ Description:
                (RO) indicates whether or not the kernel directly supports
                modifying the crash elfcorehdr for CPU hot un/plug and/or
                on/offline changes.
+
+What:          /sys/devices/system/cpu/enabled
+Date:          Nov 2022
+Contact:       Linux kernel mailing list <linux-kernel@vger.kernel.org>
+Description:
+               (RO) the list of CPUs that can be brought online.

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 1487cd9761a441bc67a12296f330081a96a9245f..b57326fd48d4dba82005476fde01c500c6602179 100644 (file)
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -95,6 +95,7 @@ void unregister_cpu(struct cpu *cpu)
 {
        int logical_cpu = cpu->dev.id;
 
+       set_cpu_enabled(logical_cpu, false);
        unregister_cpu_under_node(logical_cpu, cpu_to_node(logical_cpu));
 
        device_unregister(&cpu->dev);
@@ -273,6 +274,13 @@ static ssize_t print_cpus_offline(struct device *dev,
 }
 static DEVICE_ATTR(offline, 0444, print_cpus_offline, NULL);
 
+static ssize_t print_cpus_enabled(struct device *dev,
+                                 struct device_attribute *attr, char *buf)
+{
+       return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(cpu_enabled_mask));
+}
+static DEVICE_ATTR(enabled, 0444, print_cpus_enabled, NULL);
+
 static ssize_t print_cpus_isolated(struct device *dev,
                                  struct device_attribute *attr, char *buf)
 {
@@ -413,6 +421,7 @@ int register_cpu(struct cpu *cpu, int num)
        register_cpu_under_node(num, cpu_to_node(num));
        dev_pm_qos_expose_latency_limit(&cpu->dev,
                                        PM_QOS_RESUME_LATENCY_NO_CONSTRAINT);
+       set_cpu_enabled(num, true);
 
        return 0;
 }
@@ -494,6 +503,7 @@ static struct attribute *cpu_root_attrs[] = {
        &cpu_attrs[2].attr.attr,
        &dev_attr_kernel_max.attr,
        &dev_attr_offline.attr,
+       &dev_attr_enabled.attr,
        &dev_attr_isolated.attr,
 #ifdef CONFIG_NO_HZ_FULL
        &dev_attr_nohz_full.attr,

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 23686bed441d005974cef4b73cd920ff2c894da0..954d4adc8f81c914bb298189ae36bea661b5aa0f 100644 (file)
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -93,6 +93,7 @@ static inline void set_nr_cpu_ids(unsigned int nr)
  *
  *     cpu_possible_mask- has bit 'cpu' set iff cpu is populatable
  *     cpu_present_mask - has bit 'cpu' set iff cpu is populated
+ *     cpu_enabled_mask  - has bit 'cpu' set iff cpu can be brought online
  *     cpu_online_mask  - has bit 'cpu' set iff cpu available to scheduler
  *     cpu_active_mask  - has bit 'cpu' set iff cpu available to migration
  *
@@ -125,11 +126,13 @@ static inline void set_nr_cpu_ids(unsigned int nr)
 
 extern struct cpumask __cpu_possible_mask;
 extern struct cpumask __cpu_online_mask;
+extern struct cpumask __cpu_enabled_mask;
 extern struct cpumask __cpu_present_mask;
 extern struct cpumask __cpu_active_mask;
 extern struct cpumask __cpu_dying_mask;
 #define cpu_possible_mask ((const struct cpumask *)&__cpu_possible_mask)
 #define cpu_online_mask   ((const struct cpumask *)&__cpu_online_mask)
+#define cpu_enabled_mask   ((const struct cpumask *)&__cpu_enabled_mask)
 #define cpu_present_mask  ((const struct cpumask *)&__cpu_present_mask)
 #define cpu_active_mask   ((const struct cpumask *)&__cpu_active_mask)
 #define cpu_dying_mask    ((const struct cpumask *)&__cpu_dying_mask)
@@ -1075,6 +1078,7 @@ extern const DECLARE_BITMAP(cpu_all_bits, NR_CPUS);
 #else
 #define for_each_possible_cpu(cpu) for_each_cpu((cpu), cpu_possible_mask)
 #define for_each_online_cpu(cpu)   for_each_cpu((cpu), cpu_online_mask)
+#define for_each_enabled_cpu(cpu)   for_each_cpu((cpu), cpu_enabled_mask)
 #define for_each_present_cpu(cpu)  for_each_cpu((cpu), cpu_present_mask)
 #endif
 
@@ -1092,6 +1096,15 @@ set_cpu_possible(unsigned int cpu, bool possible)
                cpumask_clear_cpu(cpu, &__cpu_possible_mask);
 }
 
+static inline void
+set_cpu_enabled(unsigned int cpu, bool can_be_onlined)
+{
+       if (can_be_onlined)
+               cpumask_set_cpu(cpu, &__cpu_enabled_mask);
+       else
+               cpumask_clear_cpu(cpu, &__cpu_enabled_mask);
+}
+
 static inline void
 set_cpu_present(unsigned int cpu, bool present)
 {
@@ -1173,6 +1186,7 @@ static __always_inline unsigned int num_online_cpus(void)
        return raw_atomic_read(&__num_online_cpus);
 }
 #define num_possible_cpus()    cpumask_weight(cpu_possible_mask)
+#define num_enabled_cpus()     cpumask_weight(cpu_enabled_mask)
 #define num_present_cpus()     cpumask_weight(cpu_present_mask)
 #define num_active_cpus()      cpumask_weight(cpu_active_mask)
 
@@ -1181,6 +1195,11 @@ static inline bool cpu_online(unsigned int cpu)
        return cpumask_test_cpu(cpu, cpu_online_mask);
 }
 
+static inline bool cpu_enabled(unsigned int cpu)
+{
+       return cpumask_test_cpu(cpu, cpu_enabled_mask);
+}
+
 static inline bool cpu_possible(unsigned int cpu)
 {
        return cpumask_test_cpu(cpu, cpu_possible_mask);
@@ -1205,6 +1224,7 @@ static inline bool cpu_dying(unsigned int cpu)
 
 #define num_online_cpus()      1U
 #define num_possible_cpus()    1U
+#define num_enabled_cpus()     1U
 #define num_present_cpus()     1U
 #define num_active_cpus()      1U
 
@@ -1218,6 +1238,11 @@ static inline bool cpu_possible(unsigned int cpu)
        return cpu == 0;
 }
 
+static inline bool cpu_enabled(unsigned int cpu)
+{
+       return cpu == 0;
+}
+
 static inline bool cpu_present(unsigned int cpu)
 {
        return cpu == 0;

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 563877d6c28b65f40a9e5597c865e0afa1200a64..a2f3ad276814db2d113f0bfe844123217432cadd 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -3069,6 +3069,9 @@ EXPORT_SYMBOL(__cpu_possible_mask);
 struct cpumask __cpu_online_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_online_mask);
 
+struct cpumask __cpu_enabled_mask __read_mostly;
+EXPORT_SYMBOL(__cpu_enabled_mask);
+
 struct cpumask __cpu_present_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_present_mask);