here is the next patch for UML/s390 preparation.
If new_mm() has a vaild from_fd, it copies the LDT of
from_mm to new_mm using MM_COPY_SEGMENTS.
IMHO, this is arch specific.
So I shifted it to init_new_ldt() in ldt.c. I did this
for i386 only, because x86_64 doesn't have an ldt.c (yet?)
The patch applies on top of the latest LDT fixes/improvements
that AFAIK already are merged in your tree.