1 files changed, 190 insertions, 0 deletions
diff --git a/arch/x86/kernel/cpuid.c b/arch/x86/kernel/cpuid.c
new file mode 100644
index 000000000..6f7b8cc1b
--- /dev/null
+++ b/arch/x86/kernel/cpuid.c
@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* ----------------------------------------------------------------------- *
+ *
+ *   Copyright 2000-2008 H. Peter Anvin - All Rights Reserved
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * x86 CPUID access device
+ *
+ * This device is accessed by lseek() to the appropriate CPUID level
+ * and then read in chunks of 16 bytes.  A larger size means multiple
+ * reads of consecutive levels.
+ *
+ * The lower 32 bits of the file position is used as the incoming %eax,
+ * and the upper 32 bits of the file position as the incoming %ecx,
+ * the latter intended for "counting" eax levels like eax=4.
+ *
+ * This driver uses /dev/cpu/%d/cpuid where %d is the minor number, and on
+ * an SMP box will direct the access to CPU %d.
+ */
+
+#include <linux/module.h>
+
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/fcntl.h>
+#include <linux/init.h>
+#include <linux/poll.h>
+#include <linux/smp.h>
+#include <linux/major.h>
+#include <linux/fs.h>
+#include <linux/device.h>
+#include <linux/cpu.h>
+#include <linux/notifier.h>
+#include <linux/uaccess.h>
+#include <linux/gfp.h>
+#include <linux/completion.h>
+
+#include <asm/processor.h>
+#include <asm/msr.h>
+
+static struct class *cpuid_class;
+static enum cpuhp_state cpuhp_cpuid_state;
+
+struct cpuid_regs_done {
+	struct cpuid_regs regs;
+	struct completion done;
+};
+
+static void cpuid_smp_cpuid(void *cmd_block)
+{
+	struct cpuid_regs_done *cmd = cmd_block;
+
+	cpuid_count(cmd->regs.eax, cmd->regs.ecx,
+		    &cmd->regs.eax, &cmd->regs.ebx,
+		    &cmd->regs.ecx, &cmd->regs.edx);
+
+	complete(&cmd->done);
+}
+
+static ssize_t cpuid_read(struct file *file, char __user *buf,
+			  size_t count, loff_t *ppos)
+{
+	char __user *tmp = buf;
+	struct cpuid_regs_done cmd;
+	int cpu = iminor(file_inode(file));
+	u64 pos = *ppos;
+	ssize_t bytes = 0;
+	int err = 0;
+
+	if (count % 16)
+		return -EINVAL;	/* Invalid chunk size */
+
+	init_completion(&cmd.done);
+	for (; count; count -= 16) {
+		call_single_data_t csd;
+
+		INIT_CSD(&csd, cpuid_smp_cpuid, &cmd);
+
+		cmd.regs.eax = pos;
+		cmd.regs.ecx = pos >> 32;
+
+		err = smp_call_function_single_async(cpu, &csd);
+		if (err)
+			break;
+		wait_for_completion(&cmd.done);
+		if (copy_to_user(tmp, &cmd.regs, 16)) {
+			err = -EFAULT;
+			break;
+		}
+		tmp += 16;
+		bytes += 16;
+		*ppos = ++pos;
+		reinit_completion(&cmd.done);
+	}
+
+	return bytes ? bytes : err;
+}
+
+static int cpuid_open(struct inode *inode, struct file *file)
+{
+	unsigned int cpu;
+	struct cpuinfo_x86 *c;
+
+	cpu = iminor(file_inode(file));
+	if (cpu >= nr_cpu_ids || !cpu_online(cpu))
+		return -ENXIO;	/* No such CPU */
+
+	c = &cpu_data(cpu);
+	if (c->cpuid_level < 0)
+		return -EIO;	/* CPUID not supported */
+
+	return 0;
+}
+
+/*
+ * File operations we support
+ */
+static const struct file_operations cpuid_fops = {
+	.owner = THIS_MODULE,
+	.llseek = no_seek_end_llseek,
+	.read = cpuid_read,
+	.open = cpuid_open,
+};
+
+static int cpuid_device_create(unsigned int cpu)
+{
+	struct device *dev;
+
+	dev = device_create(cpuid_class, NULL, MKDEV(CPUID_MAJOR, cpu), NULL,
+			    "cpu%d", cpu);
+	return PTR_ERR_OR_ZERO(dev);
+}
+
+static int cpuid_device_destroy(unsigned int cpu)
+{
+	device_destroy(cpuid_class, MKDEV(CPUID_MAJOR, cpu));
+	return 0;
+}
+
+static char *cpuid_devnode(struct device *dev, umode_t *mode)
+{
+	return kasprintf(GFP_KERNEL, "cpu/%u/cpuid", MINOR(dev->devt));
+}
+
+static int __init cpuid_init(void)
+{
+	int err;
+
+	if (__register_chrdev(CPUID_MAJOR, 0, NR_CPUS,
+			      "cpu/cpuid", &cpuid_fops)) {
+		printk(KERN_ERR "cpuid: unable to get major %d for cpuid\n",
+		       CPUID_MAJOR);
+		return -EBUSY;
+	}
+	cpuid_class = class_create(THIS_MODULE, "cpuid");
+	if (IS_ERR(cpuid_class)) {
+		err = PTR_ERR(cpuid_class);
+		goto out_chrdev;
+	}
+	cpuid_class->devnode = cpuid_devnode;
+
+	err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/cpuid:online",
+				cpuid_device_create, cpuid_device_destroy);
+	if (err < 0)
+		goto out_class;
+
+	cpuhp_cpuid_state = err;
+	return 0;
+
+out_class:
+	class_destroy(cpuid_class);
+out_chrdev:
+	__unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
+	return err;
+}
+module_init(cpuid_init);
+
+static void __exit cpuid_exit(void)
+{
+	cpuhp_remove_state(cpuhp_cpuid_state);
+	class_destroy(cpuid_class);
+	__unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
+}
+module_exit(cpuid_exit);
+
+MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
+MODULE_DESCRIPTION("x86 generic CPUID driver");
+MODULE_LICENSE("GPL");