when comparing the e820 direct from BIOS, and the one by kexec:

 BIOS-provided physical RAM map:
- BIOS-e820: 0000000000000000 - 0000000000097400 (usable)
+ BIOS-e820: 0000000000000100 - 0000000000097400 (usable)
  BIOS-e820: 0000000000097400 - 00000000000a0000 (reserved)
  BIOS-e820: 00000000000e6000 - 0000000000100000 (reserved)
  BIOS-e820: 0000000000100000 - 00000000dffa0000 (usable)
- BIOS-e820: 00000000dffae000 - 00000000dffb0000 type 9
+ BIOS-e820: 00000000dffae000 - 00000000dffb0000 (reserved)
  BIOS-e820: 00000000dffb0000 - 00000000dffbe000 (ACPI data)
  BIOS-e820: 00000000dffbe000 - 00000000dfff0000 (ACPI NVS)
  BIOS-e820: 00000000dfff0000 - 00000000e0000000 (reserved)
  BIOS-e820: 00000000fec00000 - 00000000fec01000 (reserved)
- BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
             =======> that is the local apic address... somewhere we lost it
  BIOS-e820: 00000000ff700000 - 0000000100000000 (reserved)
  BIOS-e820: 0000000100000000 - 0000004020000000 (usable)

found one entry about reserved is missing for the kernel by kexec.

it turns out init_apic_mappings is called before e820_reserve_resources
in setup_arch. but e820_reserve_resources is using request_resource.
it will not handle the conflicts.

there are three ways to fix it:

1. change request_resource in e820_reserve_resources to to insert_resource
2. move init_apic_mappings after e820_reserve_resources
3. use late_initcall to insert lapic resource.

this patch is using method 3, that is less intrusive.

in later version could consider to use method 1.

before patch
fed20000-ffffffff : PCI Bus #00
  fee00000-fee00fff : Local APIC
  fefff000-feffffff : pnp 00:09
  ff700000-ffffffff : reserved

with patch will get map in first kernel

fed20000-ffffffff : PCI Bus #00
  fee00000-fee00fff : Local APIC
    fee00000-fee00fff : reserved
  fefff000-feffffff : pnp 00:09
  ff700000-ffffffff : reserved
Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>