Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r267651 (by attilio):
Add the possibility to specify ecx when performing cpuid calls.

MFC r267673:
Restore the ABI of the cpuctl(4) ioctl request CPUCTL_CPUID.

MFC r267814:
Make cpuctl_do_cpuid() and cpuctl_do_cpuid_count() return void.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

- Add support to atomically set/clear individual bits of a MSR register
via cpuctl(4) driver. Two new CPUCTL_MSRSBIT and CPUCTL_MSRCBIT ioctl(2)
calls treat the data field of the argument struct passed as a mask
and set/clear bits of the MSR register according to the mask value.
- Allow user to perform atomic bitwise AND and OR operaions on MSR registers
via cpucontrol(8) utility. Two new operations ("&=" and "|=") have been
added. The first one applies bitwise AND operaion between the current
contents of the MSR register and the mask, and the second performs bitwise
OR. The argument can be optionally prefixed with "~" inversion operator.
This allows one to mimic the "clear bit" behavior by using the command
like this:
cpucontrol -m 0x10&=~0x02 # clear the second bit of TSC MSR

Inversion operator support in all modes (assignment, OR, AND).

Approved by: re (kib)
MFC after: 1 month

- Add cpuctl(4) pseudo-device driver to provide access to some low-level
features of CPUs like reading/writing machine-specific registers,
retrieving cpuid data, and updating microcode.
- Add cpucontrol(8) utility, that provides userland access to
the features of cpuctl(4).
- Add subsequent manpages.

The cpuctl(4) device operates as follows. The pseudo-device node cpuctlX
is created for each cpu present in the systems. The pseudo-device minor
number corresponds to the cpu number in the system. The cpuctl(4) pseudo-
device allows a number of ioctl to be preformed, namely RDMSR/WRMSR/CPUID
and UPDATE. The first pair alows the caller to read/write machine-specific
registers from the correspondent CPU. cpuid data could be retrieved using
the CPUID call, and microcode updates are applied via UPDATE.

The permissions are inforced based on the pseudo-device file permissions.
RDMSR/CPUID will be allowed when the caller has read access to the device
node, while WRMSR/UPDATE will be granted only when the node is opened
for writing. There're also a number of priv(9) checks.

The cpucontrol(8) utility is intened to provide userland access to
the cpuctl(4) device features. The utility also allows one to apply
cpu microcode updates.

Currently only Intel and AMD cpus are supported and were tested.

Approved by: kib
Reviewed by: rpaulo, cokane, Peter Jeremy
MFC after: 1 month