[PATCH] x86_64: Fix SMP bootup with CONFIG_KDUMP enabled

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: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/arch/x86_64/kernel/trampoline.S b/arch/x86_64/kernel/trampoline.S
index 6d9c9a8e7d0e..23a03eb91fc7 100644
--- a/arch/x86_64/kernel/trampoline.S
+++ b/arch/x86_64/kernel/trampoline.S
@@ -42,8 +42,15 @@ r_base = .
         movl    $0xA5A5A5A5, trampoline_data - r_base
                                 # write marker for master knows we're running
 
-        lidt    idt_48 - r_base # load idt with 0, 0
-        lgdt    gdt_48 - r_base # load gdt with whatever is appropriate
+        /*
+         * GDT tables in non default location kernel can be beyond 16MB and
+         * lgdt will not be able to load the address as in real mode default
+         * operand size is 16bit. Use lgdtl instead to force operand size
+         * to 32 bit.
+         */
+
+        lidtl   idt_48 - r_base # load idt with 0, 0
+        lgdtl   gdt_48 - r_base # load gdt with whatever is appropriate
 
         xor     %ax, %ax
         inc     %ax             # protected mode (PE) bit