o This fix was posted for i386 long back. Posting it for x86_64.

  http://marc.theaimsgroup.com/?l=linux-kernel&m=110380103229830&w=2

o This patch fixes the problem of secondary cpus boot up. This situation
  is faced when kernel is built for default locations like 16MB and
  onwards. In this configuration, only primary cpu (BP) comes and
  secondary cpus don't boot.

o Problem occurs because in trampoline code, lgdt is not able to load the
  GDT as it happens to be situated beyond 16MB. This is due to the fact
  that cpu is still in real mode and default operand size is 16bit.

o This patch uses lgdtl instead of lgdt to force operand size to 32
  instead of 16.
Signed-off-by: NVivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>