The following patch appears sound according to an audit to ensure that all
of the codepaths where it was introduced were called after the APIC
fixmappings were set up.

This patch introduces get_physical_broadcast(), which checks the version ID
of the local APIC to determine whether it's a serial APIC or xAPIC, and
returns the correct physical broadcast ID.  It replaces all uses of
APIC_BROADCAST_ID and IO_APIC_MAX_ID with this in order to ensure.  It also
changes the checks during MP table parsing so the APIC ID is checked in
tandem with the version number.

I'm holding out for some kind of testing to get an idea of whether this
covers the cases or introduces regressions, or whatever.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>