CPUCTL(4)

NAME
cpuctl - cpuctl pseudo device

SYNOPSIS
To compile this driver into the kernel, place the following lines in your kernel configuration file:

device cpuctl

Alternatively, to load the driver as a module at boot time, place the following in loader.conf(5):

    cpuctl_load="YES"

DESCRIPTION
The special device /dev/cpuctl presents interface to the system CPU. It provides functionality to retrieve CPUID information, read/write machine specific registers (MSR) and perform CPU firmware updates.

For each CPU present in the system, the special device /dev/cpuctl%d with the appropriate index will be created. For multicore CPUs such a special device will be created for each core.

Currently, only x86_64 processors are supported.

IOCTL INTERFACE
All of the supported operations are invoked using the ioctl(2) system call. Currently, the following ioctls are defined:

CPUCTL_RDMSR cpuctl_msr_args_t *args

CPUCTL_WRMSR cpuctl_msr_args_t *args
    Read/write CPU machine specific register. The cpuctl_msr_args_t structure is defined in <sys/cpuctl.h> as:

        typedef struct {
        	int		msr;	/* MSR to read */
        	uint64_t	data;
        } cpuctl_msr_args_t;

CPUCTL_MSRSBIT cpuctl_msr_args_t *args

CPUCTL_MSRCBIT cpuctl_msr_args_t *args
    Set/clear MSR bits according to the mask given in the data field.

CPUCTL_CPUID cpuctl_cpuid_args_t *args
    Retrieve CPUID information. Arguments are supplied in the following structure:

        typedef struct {
        	int		level;		/* CPUID level */
        	uint32_t	data[4];
        } cpuctl_cpuid_args_t;

    It is equivalent to the CPUCTL_CPUID_COUNT request with level_type set to 0.

CPUCTL_CPUID_COUNT cpuctl_cpuid_count_args_t *args
    Retrieve CPUID information. Arguments are supplied in the following structure:

        typedef struct {
        	int		level;		/* CPUID level */
        	int		level_type;	/* CPUID level type */
        	uint32_t	data[4];
        } cpuctl_cpuid_count_args_t;

    The level field indicates the CPUID level to retrieve, it is loaded into the %eax register before the CPUID instruction is executed, The level_type field indicates the CPUID level type to retrieve, it is loaded into the %ecx register.

    The data field is used to store the received CPUID data. That is, data[0] contains the value of %eax register after the CPUID instruction is executed, data[1] is for %ebx, data[2] for %ecx, and data[3] for %edx.

CPUCTL_UPDATE cpuctl_update_args_t *args
    Update CPU firmware (microcode). The structure is defined in <sys/cpuctl.h> as:

        typedef struct {
        	void	*data;
        	size_t	size;
        } cpuctl_update_args_t;

    The data field should point to the firmware image of size size.

For additional information refer to cpuctl.h.

FILES
/dev/cpuctl

ERRORS

[ENXIO]
    The operation requested is not supported by the device (e.g., unsupported architecture or the CPU is disabled).

[EINVAL]
    Incorrect request was supplied, or microcode image is not correct.

[ENOMEM]
    No physical memory was available to complete the request.

[EFAULT]
    The firmware image address points outside the process address space.

SEE ALSO
cpucontrol(8)

HISTORY
The cpuctl driver first appeared in FreeBSD 7.2.

AUTHORS
The cpuctl module and this manual page were written by Stanislav Sedov <stas@FreeBSD.org>.

BUGS
Yes, probably, report if any.