current_cpu_data invokes smp_processor_id(), which is inadvisable when
preemption is enabled.  Switch to boot_cpu_data instead.

Resolves sourceforge bug 1621401.
Signed-off-by: Avi Kivity <avi@qumranet.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>