1// SPDX-License-Identifier: GPL-2.0-or-later
2/* ----------------------------------------------------------------------- *
3 *
4 * Copyright 2000-2008 H. Peter Anvin - All Rights Reserved
5 *
6 * ----------------------------------------------------------------------- */
7
8/*
9 * x86 CPUID access device
10 *
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.
14 *
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.
18 *
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.
21 */
22
23#include <linux/module.h>
24
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>
32#include <linux/fs.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>
39
40#include <asm/processor.h>
41#include <asm/msr.h>
42
43static enum cpuhp_state cpuhp_cpuid_state;
44
45struct cpuid_regs_done {
46 struct cpuid_regs regs;
47 struct completion done;
48};
49
50static void cpuid_smp_cpuid(void *cmd_block)
51{
52 struct cpuid_regs_done *cmd = cmd_block;
53
54 cpuid_count(op: cmd->regs.eax, count: cmd->regs.ecx,
55 eax: &cmd->regs.eax, ebx: &cmd->regs.ebx,
56 ecx: &cmd->regs.ecx, edx: &cmd->regs.edx);
57
58 complete(&cmd->done);
59}
60
61static ssize_t cpuid_read(struct file *file, char __user *buf,
62 size_t count, loff_t *ppos)
63{
64 char __user *tmp = buf;
65 struct cpuid_regs_done cmd;
66 int cpu = iminor(inode: file_inode(f: file));
67 u64 pos = *ppos;
68 ssize_t bytes = 0;
69 int err = 0;
70
71 if (count % 16)
72 return -EINVAL; /* Invalid chunk size */
73
74 init_completion(x: &cmd.done);
75 for (; count; count -= 16) {
76 call_single_data_t csd;
77
78 INIT_CSD(&csd, cpuid_smp_cpuid, &cmd);
79
80 cmd.regs.eax = pos;
81 cmd.regs.ecx = pos >> 32;
82
83 err = smp_call_function_single_async(cpu, csd: &csd);
84 if (err)
85 break;
86 wait_for_completion(&cmd.done);
87 if (copy_to_user(to: tmp, from: &cmd.regs, n: 16)) {
88 err = -EFAULT;
89 break;
90 }
91 tmp += 16;
92 bytes += 16;
93 *ppos = ++pos;
94 reinit_completion(x: &cmd.done);
95 }
96
97 return bytes ? bytes : err;
98}
99
100static int cpuid_open(struct inode *inode, struct file *file)
101{
102 unsigned int cpu;
103 struct cpuinfo_x86 *c;
104
105 cpu = iminor(inode: file_inode(f: file));
106 if (cpu >= nr_cpu_ids || !cpu_online(cpu))
107 return -ENXIO; /* No such CPU */
108
109 c = &cpu_data(cpu);
110 if (c->cpuid_level < 0)
111 return -EIO; /* CPUID not supported */
112
113 return 0;
114}
115
116/*
117 * File operations we support
118 */
119static const struct file_operations cpuid_fops = {
120 .owner = THIS_MODULE,
121 .llseek = no_seek_end_llseek,
122 .read = cpuid_read,
123 .open = cpuid_open,
124};
125
126static char *cpuid_devnode(const struct device *dev, umode_t *mode)
127{
128 return kasprintf(GFP_KERNEL, fmt: "cpu/%u/cpuid", MINOR(dev->devt));
129}
130
131static const struct class cpuid_class = {
132 .name = "cpuid",
133 .devnode = cpuid_devnode,
134};
135
136static int cpuid_device_create(unsigned int cpu)
137{
138 struct device *dev;
139
140 dev = device_create(cls: &cpuid_class, NULL, MKDEV(CPUID_MAJOR, cpu), NULL,
141 fmt: "cpu%d", cpu);
142 return PTR_ERR_OR_ZERO(ptr: dev);
143}
144
145static int cpuid_device_destroy(unsigned int cpu)
146{
147 device_destroy(cls: &cpuid_class, MKDEV(CPUID_MAJOR, cpu));
148 return 0;
149}
150
151static int __init cpuid_init(void)
152{
153 int err;
154
155 if (__register_chrdev(CPUID_MAJOR, baseminor: 0, NR_CPUS,
156 name: "cpu/cpuid", fops: &cpuid_fops)) {
157 printk(KERN_ERR "cpuid: unable to get major %d for cpuid\n",
158 CPUID_MAJOR);
159 return -EBUSY;
160 }
161 err = class_register(class: &cpuid_class);
162 if (err)
163 goto out_chrdev;
164
165 err = cpuhp_setup_state(state: CPUHP_AP_ONLINE_DYN, name: "x86/cpuid:online",
166 startup: cpuid_device_create, teardown: cpuid_device_destroy);
167 if (err < 0)
168 goto out_class;
169
170 cpuhp_cpuid_state = err;
171 return 0;
172
173out_class:
174 class_unregister(class: &cpuid_class);
175out_chrdev:
176 __unregister_chrdev(CPUID_MAJOR, baseminor: 0, NR_CPUS, name: "cpu/cpuid");
177 return err;
178}
179module_init(cpuid_init);
180
181static void __exit cpuid_exit(void)
182{
183 cpuhp_remove_state(state: cpuhp_cpuid_state);
184 class_unregister(class: &cpuid_class);
185 __unregister_chrdev(CPUID_MAJOR, baseminor: 0, NR_CPUS, name: "cpu/cpuid");
186}
187module_exit(cpuid_exit);
188
189MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
190MODULE_DESCRIPTION("x86 generic CPUID driver");
191MODULE_LICENSE("GPL");
192

source code of linux/arch/x86/kernel/cpuid.c