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
43 static enum cpuhp_state cpuhp_cpuid_state;
44
45 struct cpuid_regs_done {
46 struct cpuid_regs regs;
47 struct completion done;
48 };
49
cpuid_smp_cpuid(void * cmd_block)50 static void cpuid_smp_cpuid(void *cmd_block)
51 {
52 struct cpuid_regs_done *cmd = cmd_block;
53
54 cpuid_count(cmd->regs.eax, cmd->regs.ecx,
55 &cmd->regs.eax, &cmd->regs.ebx,
56 &cmd->regs.ecx, &cmd->regs.edx);
57
58 complete(&cmd->done);
59 }
60
cpuid_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)61 static 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(file_inode(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(&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);
84 if (err)
85 break;
86 wait_for_completion(&cmd.done);
87 if (copy_to_user(tmp, &cmd.regs, 16)) {
88 err = -EFAULT;
89 break;
90 }
91 tmp += 16;
92 bytes += 16;
93 *ppos = ++pos;
94 reinit_completion(&cmd.done);
95 }
96
97 return bytes ? bytes : err;
98 }
99
cpuid_open(struct inode * inode,struct file * file)100 static int cpuid_open(struct inode *inode, struct file *file)
101 {
102 unsigned int cpu;
103 struct cpuinfo_x86 *c;
104
105 cpu = iminor(file_inode(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 */
119 static 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
cpuid_devnode(const struct device * dev,umode_t * mode)126 static char *cpuid_devnode(const struct device *dev, umode_t *mode)
127 {
128 return kasprintf(GFP_KERNEL, "cpu/%u/cpuid", MINOR(dev->devt));
129 }
130
131 static const struct class cpuid_class = {
132 .name = "cpuid",
133 .devnode = cpuid_devnode,
134 };
135
cpuid_device_create(unsigned int cpu)136 static int cpuid_device_create(unsigned int cpu)
137 {
138 struct device *dev;
139
140 dev = device_create(&cpuid_class, NULL, MKDEV(CPUID_MAJOR, cpu), NULL,
141 "cpu%d", cpu);
142 return PTR_ERR_OR_ZERO(dev);
143 }
144
cpuid_device_destroy(unsigned int cpu)145 static int cpuid_device_destroy(unsigned int cpu)
146 {
147 device_destroy(&cpuid_class, MKDEV(CPUID_MAJOR, cpu));
148 return 0;
149 }
150
cpuid_init(void)151 static int __init cpuid_init(void)
152 {
153 int err;
154
155 if (__register_chrdev(CPUID_MAJOR, 0, NR_CPUS,
156 "cpu/cpuid", &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(&cpuid_class);
162 if (err)
163 goto out_chrdev;
164
165 err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/cpuid:online",
166 cpuid_device_create, cpuid_device_destroy);
167 if (err < 0)
168 goto out_class;
169
170 cpuhp_cpuid_state = err;
171 return 0;
172
173 out_class:
174 class_unregister(&cpuid_class);
175 out_chrdev:
176 __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
177 return err;
178 }
179 module_init(cpuid_init);
180
cpuid_exit(void)181 static void __exit cpuid_exit(void)
182 {
183 cpuhp_remove_state(cpuhp_cpuid_state);
184 class_unregister(&cpuid_class);
185 __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
186 }
187 module_exit(cpuid_exit);
188
189 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
190 MODULE_DESCRIPTION("x86 generic CPUID driver");
191 MODULE_LICENSE("GPL");
192