2022-10-11 11:56:24

by Jiaxun Yang

Subject: [PATCH v6] MIPS: Expose prid and globalnumber to sysfs

Some application would like to know precise model and rev of processor
to do errata workaround or optimization.

Expose them in sysfs as:
/sys/devices/system/cpu/cpuX/regs/identification/prid
/sys/devices/system/cpu/cpuX/regs/identification/globalnumber

Reusing AArch64 CPU registers directory.

Signed-off-by: Jiaxun Yang <[email protected]>
---
v2: Drop static qualifier for kobj (gregkh)
v3: Use kzalloc to allocate struct cpuregs.
note: When Greg mentioned about static I was thinking about
static qualifier of percpu variable. After reading documents
again it turns out kobjs should be allocated at runtime. Arm64's
cpuinfo kobj is also on a percpu variable... I guess that was a
intentional use?
v4: Properly handle err of kobj creation. (gregkh)
v5: Drop invalid kfree
v6: Correct offline routine, use kobject_put
---
.../ABI/testing/sysfs-devices-system-cpu | 9 ++
arch/mips/kernel/topology.c | 97 +++++++++++++++++++
2 files changed, 106 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 5bf61881f012..9dea45ad5a22 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -512,6 +512,15 @@ Description: information about CPUs heterogeneity.

cpu_capacity: capacity of cpuX.

+What: /sys/devices/system/cpu/cpuX/regs/identification/prid
+ /sys/devices/system/cpu/cpuX/regs/identification/globalnumber
+Date: October 2022
+Contact: Linux MIPS Kernel Mailing list <[email protected]>
+Description: MIPS CPU registers
+
+ 'identification' directory exposes the Processor ID and Global Number
+ registers for identifying model and revision of the CPU.
+
What: /sys/devices/system/cpu/vulnerabilities
/sys/devices/system/cpu/vulnerabilities/meltdown
/sys/devices/system/cpu/vulnerabilities/spectre_v1
diff --git a/arch/mips/kernel/topology.c b/arch/mips/kernel/topology.c
index 9429d85a4703..85588ffd6bac 100644
--- a/arch/mips/kernel/topology.c
+++ b/arch/mips/kernel/topology.c
@@ -5,6 +5,8 @@
#include <linux/node.h>
#include <linux/nodemask.h>
#include <linux/percpu.h>
+#include <linux/seq_file.h>
+#include <linux/smp.h>

static DEFINE_PER_CPU(struct cpu, cpu_devices);

@@ -26,3 +28,98 @@ static int __init topology_init(void)
}

subsys_initcall(topology_init);
+
+static struct kobj_type cpuregs_kobj_type = {
+ .sysfs_ops = &kobj_sysfs_ops,
+};
+
+struct cpureg {
+ struct kobject kobj;
+ struct cpuinfo_mips *info;
+};
+static DEFINE_PER_CPU(struct cpureg *, cpuregs);
+
+#define kobj_to_cpureg(kobj) container_of(kobj, struct cpureg, kobj)
+#define CPUREGS_ATTR_RO(_name, _field) \
+ static ssize_t _name##_show(struct kobject *kobj, \
+ struct kobj_attribute *attr, char *buf) \
+ { \
+ struct cpuinfo_mips *info = kobj_to_cpureg(kobj)->info; \
+ \
+ return sysfs_emit(buf, "0x%08x\n", info->_field); \
+ } \
+ static struct kobj_attribute cpuregs_attr_##_name = __ATTR_RO(_name)
+
+CPUREGS_ATTR_RO(prid, processor_id);
+CPUREGS_ATTR_RO(globalnumber, globalnumber);
+
+static struct attribute *cpuregs_id_attrs[] = {
+ &cpuregs_attr_prid.attr,
+ &cpuregs_attr_globalnumber.attr,
+ NULL
+};
+
+static const struct attribute_group cpuregs_attr_group = {
+ .attrs = cpuregs_id_attrs,
+ .name = "identification"
+};
+
+static int cpuregs_cpu_online(unsigned int cpu)
+{
+ int rc;
+ struct device *dev;
+ struct cpureg *reg;
+
+ dev = get_cpu_device(cpu);
+ if (!dev) {
+ rc = -ENODEV;
+ goto out;
+ }
+ reg = kzalloc(sizeof(struct cpureg), GFP_KERNEL);
+ if (!reg) {
+ rc = -ENOMEM;
+ goto out;
+ }
+ reg->info = &cpu_data[cpu];
+
+ rc = kobject_init_and_add(&reg->kobj, &cpuregs_kobj_type,
+ &dev->kobj, "regs");
+ if (rc)
+ goto out_kobj;
+ rc = sysfs_create_group(&reg->kobj, &cpuregs_attr_group);
+ if (rc)
+ goto out_kobj;
+
+ return 0;
+out_kobj:
+ kobject_put(&reg->kobj);
+out:
+ return rc;
+}
+
+static int cpuregs_cpu_offline(unsigned int cpu)
+{
+ struct cpureg *reg = per_cpu(cpuregs, cpu);
+
+ if (!reg)
+ return -ENODEV;
+ sysfs_remove_group(&reg->kobj, &cpuregs_attr_group);
+ kobject_put(&reg->kobj);
+
+ return 0;
+}
+
+static int __init cpuinfo_regs_init(void)
+{
+ int ret;
+
+ ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mips/topology:online",
+ cpuregs_cpu_online, cpuregs_cpu_offline);
+ if (ret < 0) {
+ pr_err("cpuinfo: failed to register hotplug callbacks.\n");
+ return ret;
+ }
+ return 0;
+}
+
+device_initcall(cpuinfo_regs_init);
--
2.37.0 (Apple Git-136)

2022-10-11 14:50:19

by Greg Kroah-Hartman

Subject: Re: [PATCH v6] MIPS: Expose prid and globalnumber to sysfs

On Tue, Oct 11, 2022 at 12:09:51PM +0100, Jiaxun Yang wrote:
> Some application would like to know precise model and rev of processor
> to do errata workaround or optimization.
>
> Expose them in sysfs as:
> /sys/devices/system/cpu/cpuX/regs/identification/prid
> /sys/devices/system/cpu/cpuX/regs/identification/globalnumber
>
> Reusing AArch64 CPU registers directory.
>
> Signed-off-by: Jiaxun Yang <[email protected]>
> ---
> v2: Drop static qualifier for kobj (gregkh)
> v3: Use kzalloc to allocate struct cpuregs.
> note: When Greg mentioned about static I was thinking about
> static qualifier of percpu variable. After reading documents
> again it turns out kobjs should be allocated at runtime. Arm64's
> cpuinfo kobj is also on a percpu variable... I guess that was a
> intentional use?
> v4: Properly handle err of kobj creation. (gregkh)
> v5: Drop invalid kfree
> v6: Correct offline routine, use kobject_put
> ---
> .../ABI/testing/sysfs-devices-system-cpu | 9 ++
> arch/mips/kernel/topology.c | 97 +++++++++++++++++++
> 2 files changed, 106 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index 5bf61881f012..9dea45ad5a22 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -512,6 +512,15 @@ Description: information about CPUs heterogeneity.
>
> cpu_capacity: capacity of cpuX.
>
> +What: /sys/devices/system/cpu/cpuX/regs/identification/prid
> + /sys/devices/system/cpu/cpuX/regs/identification/globalnumber
> +Date: October 2022
> +Contact: Linux MIPS Kernel Mailing list <[email protected]>
> +Description: MIPS CPU registers
> +
> + 'identification' directory exposes the Processor ID and Global Number
> + registers for identifying model and revision of the CPU.
> +
> What: /sys/devices/system/cpu/vulnerabilities
> /sys/devices/system/cpu/vulnerabilities/meltdown
> /sys/devices/system/cpu/vulnerabilities/spectre_v1
> diff --git a/arch/mips/kernel/topology.c b/arch/mips/kernel/topology.c
> index 9429d85a4703..85588ffd6bac 100644
> --- a/arch/mips/kernel/topology.c
> +++ b/arch/mips/kernel/topology.c
> @@ -5,6 +5,8 @@
> #include <linux/node.h>
> #include <linux/nodemask.h>
> #include <linux/percpu.h>
> +#include <linux/seq_file.h>
> +#include <linux/smp.h>
>
> static DEFINE_PER_CPU(struct cpu, cpu_devices);
>
> @@ -26,3 +28,98 @@ static int __init topology_init(void)
> }
>
> subsys_initcall(topology_init);
> +
> +static struct kobj_type cpuregs_kobj_type = {
> + .sysfs_ops = &kobj_sysfs_ops,
> +};
> +
> +struct cpureg {
> + struct kobject kobj;
> + struct cpuinfo_mips *info;
> +};
> +static DEFINE_PER_CPU(struct cpureg *, cpuregs);
> +
> +#define kobj_to_cpureg(kobj) container_of(kobj, struct cpureg, kobj)
> +#define CPUREGS_ATTR_RO(_name, _field) \
> + static ssize_t _name##_show(struct kobject *kobj, \
> + struct kobj_attribute *attr, char *buf) \
> + { \
> + struct cpuinfo_mips *info = kobj_to_cpureg(kobj)->info; \
> + \
> + return sysfs_emit(buf, "0x%08x\n", info->_field); \
> + } \
> + static struct kobj_attribute cpuregs_attr_##_name = __ATTR_RO(_name)
> +
> +CPUREGS_ATTR_RO(prid, processor_id);
> +CPUREGS_ATTR_RO(globalnumber, globalnumber);
> +
> +static struct attribute *cpuregs_id_attrs[] = {
> + &cpuregs_attr_prid.attr,
> + &cpuregs_attr_globalnumber.attr,
> + NULL
> +};
> +
> +static const struct attribute_group cpuregs_attr_group = {
> + .attrs = cpuregs_id_attrs,
> + .name = "identification"
> +};
> +
> +static int cpuregs_cpu_online(unsigned int cpu)
> +{
> + int rc;
> + struct device *dev;
> + struct cpureg *reg;
> +
> + dev = get_cpu_device(cpu);
> + if (!dev) {
> + rc = -ENODEV;
> + goto out;
> + }
> + reg = kzalloc(sizeof(struct cpureg), GFP_KERNEL);
> + if (!reg) {
> + rc = -ENOMEM;
> + goto out;
> + }
> + reg->info = &cpu_data[cpu];
> +
> + rc = kobject_init_and_add(&reg->kobj, &cpuregs_kobj_type,
> + &dev->kobj, "regs");
> + if (rc)
> + goto out_kobj;
> + rc = sysfs_create_group(&reg->kobj, &cpuregs_attr_group);
> + if (rc)
> + goto out_kobj;
> +
> + return 0;
> +out_kobj:
> + kobject_put(&reg->kobj);
> +out:
> + return rc;
> +}
> +
> +static int cpuregs_cpu_offline(unsigned int cpu)
> +{
> + struct cpureg *reg = per_cpu(cpuregs, cpu);
> +
> + if (!reg)
> + return -ENODEV;
> + sysfs_remove_group(&reg->kobj, &cpuregs_attr_group);
> + kobject_put(&reg->kobj);

You did not test this code :(

Please do so, and also exercise the cpu-remove path and fix up all the
errors that happen there.

thanks,

greg k-h