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