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