port-i386/52266: Double fault early in boot with Transmeta Crusoe CPU

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         52266
>Category:       port-i386
>Synopsis:       Double fault early in boot with Transmeta Crusoe CPU
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    port-i386-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed May 31 12:55:00 +0000 2017
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date >= 2017.05.23.08.54.39
>Organization:

>Environment:
System: NetBSD
Architecture: i386
Machine: i386
>Description:

I have an old NEC Versa Daylite laptop with a Transmeta Crusoe CPU
running NetBSD/i386.  I recently tried to upgrade the kernel to
-current, but it crashed very early in the boot, immediately after
printing the kernel segment sizes, with the following message
(transcribed manually):

  Fatal double fault in supervisor mode
  Trap type 13 code 0xc0116f29 eip 0x8 cs 0x296 eflags 0xc0150010 cr2 0 ilevel 0 esp 0xc08b0030
  curlwp 0xc1231920 pid 0 lid 1 lowest kstack 0xc149e2c0
  kernel: user trap double fault, code=0
  Stopped in pid 0.1 (system) at  8:      invalid adderss
  db{0}>

The keyboard does not respond to ddb commands at this point.

By bisection, I have determined that the problem appeared with the
following recent commits:

  2017.05.23.08.54.38 nonaka src/sys/arch/amd64/amd64/db_interface.c 1.25
  2017.05.23.08.54.38 nonaka src/sys/arch/amd64/amd64/mainbus.c 1.38
  2017.05.23.08.54.38 nonaka src/sys/arch/amd64/amd64/vector.S 1.49
  2017.05.23.08.54.38 nonaka src/sys/arch/amd64/include/i82093reg.h 1.8
  2017.05.23.08.54.38 nonaka src/sys/arch/i386/i386/db_interface.c 1.72
  2017.05.23.08.54.38 nonaka src/sys/arch/i386/i386/mainbus.c 1.103
  2017.05.23.08.54.38 nonaka src/sys/arch/i386/i386/vector.S 1.69
  2017.05.23.08.54.39 nonaka src/sys/arch/i386/include/i82093reg.h 1.10
  2017.05.23.08.54.39 nonaka src/sys/arch/x86/include/cpuvar.h 1.50
  2017.05.23.08.54.39 nonaka src/sys/arch/x86/include/i82489var.h 1.19
  2017.05.23.08.54.39 nonaka src/sys/arch/x86/include/intr.h 1.50
  2017.05.23.08.54.39 nonaka src/sys/arch/x86/include/mpacpi.h 1.11
  2017.05.23.08.54.39 nonaka src/sys/arch/x86/pci/msipic.c 1.9
  2017.05.23.08.54.39 nonaka src/sys/arch/x86/x86/cpu.c 1.125
  2017.05.23.08.54.39 nonaka src/sys/arch/x86/x86/lapic.c 1.58
  2017.05.23.08.54.39 nonaka src/sys/arch/x86/x86/pmc.c 1.7
  2017.05.23.08.54.39 nonaka src/sys/arch/x86/x86/tprof_amdpmi.c 1.7
  2017.05.23.08.54.39 nonaka src/sys/arch/x86/x86/tprof_pmi.c 1.14
  2017.05.23.08.54.39 nonaka src/sys/arch/xen/include/intr.h 1.40
  2017.05.23.08.54.39 nonaka src/sys/arch/xen/include/mpacpi.h 1.2
  2017.05.23.08.54.39 nonaka src/sys/arch/xen/x86/intr.c 1.31
  2017.05.23.08.54.39 nonaka src/sys/arch/xen/x86/mainbus.c 1.19

>How-To-Repeat:

Attempt to boot NetBSD-current/i386 on a Transmeta Crusoe CPU.

>Fix: