kern/145385: Logical processor cannot be disabled for some SMT-enabled Intel procs

[Garrett Cooper]

>Number:         145385
>Category:       kern
>Synopsis:       Logical processor cannot be disabled for some SMT-enabled Intel procs
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Apr 04 20:10:08 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator:     Garrett Cooper
>Release:        9-CURRENT
>Organization:
Cisco Systems, Inc.
>Environment:
FreeBSD bayonetta.local 9.0-CURRENT FreeBSD 9.0-CURRENT #0 r205872M: Sat Apr  3 18:14:55 PDT 2010     root at bayonetta.local:/usr/obj/usr/src/sys/BAYONETTA  amd64
>Description:
As discussed here:

http://forums.freebsd.org/showthread.php?t=12527

and here:

http://www.mail-archive.com/freebsd-hackers@freebsd.org/msg70605.html

logical CPUs cannot be disabled via machdep.hlt_logical_cpus tunable because it's incorrectly detecting that the SMT-enabled processor doesn't have hyperthreading cores (it's a Xeon X-series equivalent workstation processor, which has hyperthreading technology enabled).
>How-To-Repeat:
Boot with an X-series Xeon or Hyperthreading enabled Pentium processor chip and set `machdep.hlt_logical_cpus' to 1. The logical processors will not be disabled.
>Fix:


>Release-Note:
>Audit-Trail:
>Unformatted: