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CPUCTL(4) Device Drivers Manual CPUCTL(4)


cpuctlcpuctl pseudo device


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):


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.


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 struct:
typedef struct { 
	int		level;	/* CPUID level */ 
	uint32_t	data[4]; 
} cpuctl_cpuid_args_t;
The level field indicates the CPUID level to retrieve information for, while the data field is used to store the received CPUID data.
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.


The operation requested is not supported by the device (e.g. unsupported architecture or the CPU is disabled)
Incorrect request was supplied, or microcode image is not correct.
No physical memory was available to complete the request.
The firmware image address points outside the process address space.




hwpmc(4), cpucontrol(8)


The cpuctl driver first appeared in FreeBSD 7.2.


Yes, probably, report if any.


The cpuctl module and this manual page were written by Stanislav Sedov ⟨⟩.
June 30, 2009 Debian