head -r338804 boots threadripper 1950X fine; head -r338810+ do not; -r338807 seems implicated

[Mark Millard]

I attempted to jump from head -r334014 to -r339076
on a threadripper 1950X board and the boot fails.
This is both native booting and under Hyper-V,
same machine and root file system in both cases.

It fails just after the FreeBSD/SMP lines,
reporting "kernel trap 9 with interrupts disabled".

It fails in pmap_force_invaldiate_cache_range at
a clflusl (%rax) instruction that produces a
"Fatal trap 9: general protection fault while
in kernel mode". cpudid=0 apic id= 00

I used kernel.txz files from:

https://artifact.ci.freebsd.org/snapshot/head/r*/amd64/amd64/

to narrow the range of kernel builds for working -> failing
and got:

-r338804 boots fine
(no amd64 kernel builds between to try)
-r338810+ fails (any that I tried, anyway)

In that range is -r338807 :

QUOTE
Author: kib
Date: Wed Sep 19 19:35:02 2018
New Revision: 338807
URL: 
https://svnweb.freebsd.org/changeset/base/338807


Log:
  Convert x86 cache invalidation functions to ifuncs.
  
  This simplifies the runtime logic and reduces the number of
  runtime-constant branches.
  
  Reviewed by:	alc, markj
  Sponsored by:	The FreeBSD Foundation
  Approved by:	re (gjb)
  Differential revision:	
https://reviews.freebsd.org/D16736

Modified:
  head/sys/amd64/amd64/pmap.c
  head/sys/amd64/include/pmap.h
  head/sys/dev/drm2/drm_os_freebsd.c
  head/sys/dev/drm2/i915/intel_ringbuffer.c
  head/sys/i386/i386/pmap.c
  head/sys/i386/i386/vm_machdep.c
  head/sys/i386/include/pmap.h
  head/sys/x86/iommu/intel_utils.c
END QUOTE

There do seem to be changes associated with
clflush(...) use. Looking at:

https://svnweb.freebsd.org/base/head/sys/amd64/amd64/pmap.c?annotate=339432

it appears that pmap_force_invalidate_cache_range has not
changed since -r338807.

It seems that -r338806 and -r3388810 would be unlikely
contributors.


===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)