The basic idea is to use a the same virtual address as a window onto
distinct physical memory locations - one per processor. The physical
address that you access through this mapping depends on which cpu you
are currently executing on. We can now use the same virtual address
on any processor to access its per-cpu area.
The details are:
- The virtual address for 'struct pcpu *pcpup' is obtained by
stealing 2 pages worth of KVA in pmap_bootstrap().
- The mapping from the constant virtual address to a distinct
physical page is done in cpu_pcpu_init() through a wired TLB entry.
- A side-effect of this is that we reserve 2 pages worth of memory
for the pcpu but in reality it needs much less than that. The unused
memory is now used as the boot stack for the BSP and APs.
Remove SMP-specific bits from locore.S. The plan is to use a separate
mpboot.S for AP bootstrap.
Discussed on: freebsd-mips
Approved by: imp (mentor)
9dd3fbb0f2