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.

Debian                                            June 20, 2014                                        CPUCTL(4)