Hello experts,

I need two functions to disable and enable Hyperthreading technology
in Pentium 4 processors, resprectively.

All logical processors must be disabled except one for the cpu to
behave as a normal processor without hyperthreading. All disabled
logical processors will be resumed only by the enabling function or by
rare (as rare as possible) events such as NMI interrupt signals.

The two functions will be put into a Windows XP device driver running
in kernel mode. This means they can call privileged system routines.

Disabling and enabling must not require rebooting. 

The two functions can be written in C or assembly.

Note 1: You only need to write the two functions, not the device driver.
You can consider the single physical processor environment only, need
not multi-processor one.

Note 2: Instead of writing the two functions explicitly, you can
provide algorithms with detailed documentation. Make sure you know
that they will work.


Related material I have found so far:

1. A logical processor can be halted by the HLT instruction.
ftp://download.intel.com/design/Pentium4/manuals/25366614.pdf (pdf page 378)

2. To prevent the halted logical processors to resume by normal
interrupts, you can raise the current task priority:
ftp://download.intel.com/design/Pentium4/manuals/25366814.pdf (section 8.8.3.1)
   or by masking the maskable hardware interrupts (section 5.8.1)


Thanks a lot
ARINTEL