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// SPDX-License-Identifier: GPL-2.0-or-later
/* ----------------------------------------------------------------------- *
*
* Copyright 2000-2008 H. Peter Anvin - All Rights Reserved
*
* ----------------------------------------------------------------------- */
/*
* x86 CPUID access device
*
* This device is accessed by lseek() to the appropriate CPUID level
* and then read in chunks of 16 bytes. A larger size means multiple
* reads of consecutive levels.
*
* The lower 32 bits of the file position is used as the incoming %eax,
* and the upper 32 bits of the file position as the incoming %ecx,
* the latter intended for "counting" eax levels like eax=4.
*
* This driver uses /dev/cpu/%d/cpuid where %d is the minor number, and on
* an SMP box will direct the access to CPU %d.
*/
#include <linux/module.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/fcntl.h>
#include <linux/init.h>
#include <linux/poll.h>
#include <linux/smp.h>
#include <linux/major.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/uaccess.h>
#include <linux/gfp.h>
#include <linux/completion.h>
#include <asm/processor.h>
#include <asm/msr.h>
static struct class *cpuid_class;
static enum cpuhp_state cpuhp_cpuid_state;
struct cpuid_regs_done {
struct cpuid_regs regs;
struct completion done;
};
static void cpuid_smp_cpuid(void *cmd_block)
{
struct cpuid_regs_done *cmd = cmd_block;
cpuid_count(cmd->regs.eax, cmd->regs.ecx,
&cmd->regs.eax, &cmd->regs.ebx,
&cmd->regs.ecx, &cmd->regs.edx);
complete(&cmd->done);
}
static ssize_t cpuid_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
char __user *tmp = buf;
struct cpuid_regs_done cmd;
int cpu = iminor(file_inode(file));
u64 pos = *ppos;
ssize_t bytes = 0;
int err = 0;
if (count % 16)
return -EINVAL; /* Invalid chunk size */
init_completion(&cmd.done);
for (; count; count -= 16) {
call_single_data_t csd = {
.func = cpuid_smp_cpuid,
.info = &cmd,
};
cmd.regs.eax = pos;
cmd.regs.ecx = pos >> 32;
err = smp_call_function_single_async(cpu, &csd);
if (err)
break;
wait_for_completion(&cmd.done);
if (copy_to_user(tmp, &cmd.regs, 16)) {
err = -EFAULT;
break;
}
tmp += 16;
bytes += 16;
*ppos = ++pos;
reinit_completion(&cmd.done);
}
return bytes ? bytes : err;
}
static int cpuid_open(struct inode *inode, struct file *file)
{
unsigned int cpu;
struct cpuinfo_x86 *c;
cpu = iminor(file_inode(file));
if (cpu >= nr_cpu_ids || !cpu_online(cpu))
return -ENXIO; /* No such CPU */
c = &cpu_data(cpu);
if (c->cpuid_level < 0)
return -EIO; /* CPUID not supported */
return 0;
}
/*
* File operations we support
*/
static const struct file_operations cpuid_fops = {
.owner = THIS_MODULE,
.llseek = no_seek_end_llseek,
.read = cpuid_read,
.open = cpuid_open,
};
static int cpuid_device_create(unsigned int cpu)
{
struct device *dev;
dev = device_create(cpuid_class, NULL, MKDEV(CPUID_MAJOR, cpu), NULL,
"cpu%d", cpu);
return PTR_ERR_OR_ZERO(dev);
}
static int cpuid_device_destroy(unsigned int cpu)
{
device_destroy(cpuid_class, MKDEV(CPUID_MAJOR, cpu));
return 0;
}
static char *cpuid_devnode(struct device *dev, umode_t *mode)
{
return kasprintf(GFP_KERNEL, "cpu/%u/cpuid", MINOR(dev->devt));
}
static int __init cpuid_init(void)
{
int err;
if (__register_chrdev(CPUID_MAJOR, 0, NR_CPUS,
"cpu/cpuid", &cpuid_fops)) {
printk(KERN_ERR "cpuid: unable to get major %d for cpuid\n",
CPUID_MAJOR);
return -EBUSY;
}
cpuid_class = class_create(THIS_MODULE, "cpuid");
if (IS_ERR(cpuid_class)) {
err = PTR_ERR(cpuid_class);
goto out_chrdev;
}
cpuid_class->devnode = cpuid_devnode;
err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/cpuid:online",
cpuid_device_create, cpuid_device_destroy);
if (err < 0)
goto out_class;
cpuhp_cpuid_state = err;
return 0;
out_class:
class_destroy(cpuid_class);
out_chrdev:
__unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
return err;
}
module_init(cpuid_init);
static void __exit cpuid_exit(void)
{
cpuhp_remove_state(cpuhp_cpuid_state);
class_destroy(cpuid_class);
__unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
}
module_exit(cpuid_exit);
MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
MODULE_DESCRIPTION("x86 generic CPUID driver");
MODULE_LICENSE("GPL");
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