Fix a long standing (from the original 4.4BSD lite sources) race between
  vmspace_fork and vm_map_wire that would lead to "vm_fault_copy_wired: page
  missing" panics.  While faulting in pages for a map entry that is being
  wired down, mark the containing map as busy.  In vmspace_fork wait until
  the map is unbusy, before we try to copy the entries.

  Sponsored by:	Isilon Systems, Inc.

Approved by:	re (kib)

This commit merges the MIPS platform changes that was now stable in
-CURRENT into 8-STABLE. The MIPS changesets are too many (~400) to list
here. But the changesets merged in this commit that affect other platforms
are summarized below:

r204635 : (changes to sys/dev/hwpmc, lib/libpmc, sys/sys/pmc.h)
Add support for hwpmc(4) on the MIPS 24K, 32 bit, embedded processor.

r205845: (changes to sys/modules/Makefile)
Fix for building modules on mips and arm.

r204031: (changes to sys/kern/link_elf_obj.c)
printf fix, as part of kernel module support for MIPS.

r206404: (changes to sys/arm/include/bus.h)
Add BUS_SPACE_UNRESTRICTED and define it to be ~0, just like all the
other platforms - for arm and mips.

r206819: (changes to sys/vm/)
Add VMFS_TLB_ALIGNED_SPACE option and kmem_alloc_nofault_space(), which
is used to allocate kernel stack address on MIPS.

r208165, r211087: (sys/kern/subr_smp.c, sys/kern/sched_ule.c)
Enable ULE scheduler for MIPS, Fix for an issue in SMP when 32 cpus are
enabled.

r208659: (sys/{ia64/ia64,mips/mips,sun4v/sun4v}/pmap.c)
Simplify the inner loop of get_pv_entry()

r208794: (changes to sys/vm/)
Make vm_contig_grow_cache() extern, and use it when vm_phys_alloc_contig()
fails to allocate MIPS page table pages.

r210327:  (changes to sys/vm/)
Support for MIPS page table page allocation.  Add a new function 'vm_page_t
vm_page_alloc_freelist(int flind, int order, int req)' to vm/vm_page.c to
allocate a page from a specified freelist, and other related changes.

Reviewed by:	alc(vm changes only)
Approved by:	kib(re), alc(vm), imp(mips), jmallett(mips), gnn(mips pmc)

Implement a (soft) stack guard page for auto-growing stack mappings.

  In case the stack size reaches its limit and its growth must be
  restricted, ensure that grow_amount is a multiple of the page size.
  Otherwise, the kernel may crash in swap_reserve_by_uid() on HEAD and
  FreeBSD 8.x, and produce a core file with a missing stack on FreeBSD
  7.x.

  If vm_map_find() is asked to allocate a superpage-aligned region of
  virtual addresses that is greater than a superpage in size but not a
  multiple of the superpage size, then vm_map_find() is not always
  expanding the kernel pmap to support the last few small pages being
  allocated.  Previously, we grew the kernel page table in
  vm_map_findspace() when we found the first available virtual address.
  Now, instead, we defer the call to pmap_growkernel() until we are
  committed to a range of virtual addresses in vm_map_insert().

Adopt the deferring of object deallocation for the deleted map entries
on map unlock to the lock downgrade and later read unlock operation.

MFC r212868 (by alc) [1]:
Make refinements to r212824. Redo the implementation of
vm_map_unlock_and_wait().

Approved by:	alc [1]

Introduce a helper function vm_page_find_least(). Use it in several places,
which inline the function.

The MAP_ENTRY_NEEDS_COPY flag belongs to protoeflags, cow variable
uses different namespace.

When protection of wired read-only mapping is changed to read-write,
install new shadow object behind the map entry and copy the pages
from the underlying objects to it. This makes the mprotect(2) call to
actually perform the requested operation instead of silently do nothing
and return success, that causes SIGSEGV on later write access to the
mapping.

Reuse vm_fault_copy_entry() to do the copying, modifying it to behave
correctly when src_entry == dst_entry.

Move the annotation for vm_map_startup() immediately before the function.

Approved by:	re (bz, kensmith)