hi,
In x86_64 platform, INT1 and INT3 trap stack is IST stack called 
DEBUG_STACK, when INT1/INT3 trap happens, system will switch to 
DEBUG_STACK by hardware. Current DEBUG_STACK size is 4K, when int1/int3 
trap happens, kernel will minus current DEBUG_STACK IST value by 4k. But 
if int3/int1 trap is nested, it will destroy other vector's IST stack.
This patch modifies this, it sets DEBUG_STACK size as 8K and allows two 
level of nested int1/int3 trap.
Kprobe DEBUG_STACK may be nested, because kprobe hanlder may be probed 
by other kprobes. This patch is against 2.6.17-rc3.

Signed-Off-By: bibo, mao <bibo.mao@intel.com>

Thanks
bibo,mao