Add CPUID subleaf capability to cpuctl/cpucontrol

[Konstantin Belousov]

On Wed, Mar 26, 2014 at 11:18:02PM +0800, Jia-Shiun Li wrote:
> Hi all,
> 
> I am recently writing a small tool playing msr with cpuctl(4).
> Meanwhile I found that it is currently not passing value but 0 in ECX
> register to CPUID instruction as input. So I have the attached patch
> to do it.
> 
> ECX is used to specify sub-leaf for some EAX leaf value. For example
>   EAX=0x04: Deterministic Cache Parameters Leaf
>   EAX=0x0b: Extended Topology Enumeration Leaf
> with the attached patch user will be able to get subleaf info by
> writing applications using cpuctl(4) ioctl or by using cpucontrol(8)
> with -s flag.
> 
> Please comment.
> 
> Regards,
> Jia-Shiun.

> Index: sys/dev/cpuctl/cpuctl.c
> ===================================================================
> --- sys/dev/cpuctl/cpuctl.c	(revision 263420)
> +++ sys/dev/cpuctl/cpuctl.c	(working copy)
> @@ -204,7 +204,7 @@
>  	oldcpu = td->td_oncpu;
>  	is_bound = cpu_sched_is_bound(td);
>  	set_cpu(cpu, td);
> -	cpuid_count(data->level, 0, data->data);
> +	cpuid_count(data->level, data->sublevel, data->data);
>  	restore_cpu(oldcpu, is_bound, td);
>  	return (0);
>  }
> Index: sys/sys/cpuctl.h
> ===================================================================
> --- sys/sys/cpuctl.h	(revision 263420)
> +++ sys/sys/cpuctl.h	(working copy)
> @@ -36,6 +36,7 @@
>  
>  typedef struct {
>  	int		level;	/* CPUID level */
> +	int		sublevel; /* sublevel */
>  	uint32_t	data[4];
>  } cpuctl_cpuid_args_t;

This breaks the ABI.  If you want to extend the CPUCTL_CPUID,
define new ioctl number for the extended structure, and keep the
old arg structure and old number handled by the compat shims. Due
to the construction of the CPUCTL_CPUID using _IOWR(), you in fact
get the new number due to the structure size change.

But IMO adding this functionality to a driver does not make much sense
at all.  I remember that at time when initial version of cpuctl(4)
was written, we did not have useful implementation of cpuset(2).
Now, when it is possible to bind thread to a core from usermode,
you do not need a driver providing interface to CPUID, since CPUID
is usermode instruction.
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