1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* ----------------------------------------------------------------------- *
4 * Copyright 2000-2008 H. Peter Anvin - All Rights Reserved
6 * ----------------------------------------------------------------------- */
9 * x86 CPUID access device
11 * This device is accessed by lseek() to the appropriate CPUID level
12 * and then read in chunks of 16 bytes. A larger size means multiple
13 * reads of consecutive levels.
15 * The lower 32 bits of the file position is used as the incoming %eax,
16 * and the upper 32 bits of the file position as the incoming %ecx,
17 * the latter intended for "counting" eax levels like eax=4.
19 * This driver uses /dev/cpu/%d/cpuid where %d is the minor number, and on
20 * an SMP box will direct the access to CPU %d.
23 #include <linux/module.h>
25 #include <linux/types.h>
26 #include <linux/errno.h>
27 #include <linux/fcntl.h>
28 #include <linux/init.h>
29 #include <linux/poll.h>
30 #include <linux/smp.h>
31 #include <linux/major.h>
33 #include <linux/device.h>
34 #include <linux/cpu.h>
35 #include <linux/notifier.h>
36 #include <linux/uaccess.h>
37 #include <linux/gfp.h>
38 #include <linux/completion.h>
40 #include <asm/processor.h>
43 static struct class *cpuid_class
;
44 static enum cpuhp_state cpuhp_cpuid_state
;
46 struct cpuid_regs_done
{
47 struct cpuid_regs regs
;
48 struct completion done
;
51 static void cpuid_smp_cpuid(void *cmd_block
)
53 struct cpuid_regs_done
*cmd
= cmd_block
;
55 cpuid_count(cmd
->regs
.eax
, cmd
->regs
.ecx
,
56 &cmd
->regs
.eax
, &cmd
->regs
.ebx
,
57 &cmd
->regs
.ecx
, &cmd
->regs
.edx
);
62 static ssize_t
cpuid_read(struct file
*file
, char __user
*buf
,
63 size_t count
, loff_t
*ppos
)
65 char __user
*tmp
= buf
;
66 struct cpuid_regs_done cmd
;
67 int cpu
= iminor(file_inode(file
));
73 return -EINVAL
; /* Invalid chunk size */
75 init_completion(&cmd
.done
);
76 for (; count
; count
-= 16) {
77 call_single_data_t csd
;
79 INIT_CSD(&csd
, cpuid_smp_cpuid
, &cmd
);
82 cmd
.regs
.ecx
= pos
>> 32;
84 err
= smp_call_function_single_async(cpu
, &csd
);
87 wait_for_completion(&cmd
.done
);
88 if (copy_to_user(tmp
, &cmd
.regs
, 16)) {
95 reinit_completion(&cmd
.done
);
98 return bytes
? bytes
: err
;
101 static int cpuid_open(struct inode
*inode
, struct file
*file
)
104 struct cpuinfo_x86
*c
;
106 cpu
= iminor(file_inode(file
));
107 if (cpu
>= nr_cpu_ids
|| !cpu_online(cpu
))
108 return -ENXIO
; /* No such CPU */
111 if (c
->cpuid_level
< 0)
112 return -EIO
; /* CPUID not supported */
118 * File operations we support
120 static const struct file_operations cpuid_fops
= {
121 .owner
= THIS_MODULE
,
122 .llseek
= no_seek_end_llseek
,
127 static int cpuid_device_create(unsigned int cpu
)
131 dev
= device_create(cpuid_class
, NULL
, MKDEV(CPUID_MAJOR
, cpu
), NULL
,
133 return PTR_ERR_OR_ZERO(dev
);
136 static int cpuid_device_destroy(unsigned int cpu
)
138 device_destroy(cpuid_class
, MKDEV(CPUID_MAJOR
, cpu
));
142 static char *cpuid_devnode(struct device
*dev
, umode_t
*mode
)
144 return kasprintf(GFP_KERNEL
, "cpu/%u/cpuid", MINOR(dev
->devt
));
147 static int __init
cpuid_init(void)
151 if (__register_chrdev(CPUID_MAJOR
, 0, NR_CPUS
,
152 "cpu/cpuid", &cpuid_fops
)) {
153 printk(KERN_ERR
"cpuid: unable to get major %d for cpuid\n",
157 cpuid_class
= class_create(THIS_MODULE
, "cpuid");
158 if (IS_ERR(cpuid_class
)) {
159 err
= PTR_ERR(cpuid_class
);
162 cpuid_class
->devnode
= cpuid_devnode
;
164 err
= cpuhp_setup_state(CPUHP_AP_ONLINE_DYN
, "x86/cpuid:online",
165 cpuid_device_create
, cpuid_device_destroy
);
169 cpuhp_cpuid_state
= err
;
173 class_destroy(cpuid_class
);
175 __unregister_chrdev(CPUID_MAJOR
, 0, NR_CPUS
, "cpu/cpuid");
178 module_init(cpuid_init
);
180 static void __exit
cpuid_exit(void)
182 cpuhp_remove_state(cpuhp_cpuid_state
);
183 class_destroy(cpuid_class
);
184 __unregister_chrdev(CPUID_MAJOR
, 0, NR_CPUS
, "cpu/cpuid");
186 module_exit(cpuid_exit
);
188 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
189 MODULE_DESCRIPTION("x86 generic CPUID driver");
190 MODULE_LICENSE("GPL");