CPUCTL(4)              FreeBSD Kernel Interfaces Manual              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 i386 and amd64 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
     hwpmc(4), 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.

FreeBSD 13.1-RELEASE-p6          June 20, 2014         FreeBSD 13.1-RELEASE-p6