[PATCH] x86_64: ioapic virtual wire mode fix

o Currently, during kexec reboot, IOAPIC is re-programmed back to virtual
  wire mode if there was an i8259 connected to it. This enables getting
  timer interrupts in second kernel in legacy mode.

o After putting into virtual wire mode, IOAPIC delivers the i8259 interrupts
  to CPU0. This works well for kexec but not for kdump as we might crash
  on a different CPU and second kernel will not see timer interrupts.

o This patch modifies the redirection table entry to deliver the timer
  interrupts to the cpu we are rebooting (instead of hardcoding to zero).
  This ensures that second kernel receives timer interrupts even on a
  non-boot cpu.
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/io_apic.c

@@ -1307,7 +1307,8 @@ void disable_IO_APIC(void)
 		entry.dest_mode       = 0; /* Physical */
 		entry.delivery_mode   = dest_ExtINT; /* ExtInt */
 		entry.vector          = 0;
-		entry.dest.physical.physical_dest = 0;
+		entry.dest.physical.physical_dest =
+					GET_APIC_ID(apic_read(APIC_ID));
 
 		/*
 		 * Add it to the IO-APIC irq-routing table: