Change synchonization rules for vm_page reference counting.

There are several mechanisms by which a vm_page reference is held,
preventing the page from being freed back to the page allocator. In
particular, holding the page's object lock is sufficient to prevent the
page from being freed; holding the busy lock or a wiring is sufficent as
well. These references are protected by the page lock, which must
therefore be acquired for many per-page operations. This results in
false sharing since the page locks are external to the vm_page
structures themselves and each lock protects multiple structures.

Transition to using an atomically updated per-page reference counter.
The object's reference is counted using a flag bit in the counter. A
second flag bit is used to atomically block new references via
pmap_extract_and_hold() while removing managed mappings of a page.
Thus, the reference count of a page is guaranteed not to increase if the
page is unbusied, unmapped, and the object's write lock is held. As
a consequence of this, the page lock no longer protects a page's
identity; operations which move pages between objects are now
synchronized solely by the objects' locks.

The vm_page_wire() and vm_page_unwire() KPIs are changed. The former
requires that either the object lock or the busy lock is held. The
latter no longer has a return value and may free the page if it releases
the last reference to that page. vm_page_unwire_noq() behaves the same
as before; the caller is responsible for checking its return value and
freeing or enqueuing the page as appropriate. vm_page_wire_mapped() is
introduced for use in pmap_extract_and_hold(). It fails if the page is
concurrently being unmapped, typically triggering a fallback to the
fault handler. vm_page_wire() no longer requires the page lock and
vm_page_unwire() now internally acquires the page lock when releasing
the last wiring of a page (since the page lock still protects a page's
queue state). In particular, synchronization details are no longer
leaked into the caller.

The change excises the page lock from several frequently executed code
paths. In particular, vm_object_terminate() no longer bounces between
page locks as it releases an object's pages, and direct I/O and
sendfile(SF_NOCACHE) completions no longer require the page lock. In
these latter cases we now get linear scalability in the common scenario
where different threads are operating on different files.

__FreeBSD_version is bumped. The DRM ports have been updated to
accomodate the KPI changes.

Reviewed by: jeff (earlier version)
Tested by: gallatin (earlier version), pho
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D20486

Merge the vm_page hold and wire mechanisms.

The hold_count and wire_count fields of struct vm_page are separate
reference counters with similar semantics. The remaining essential
differences are that holds are not counted as a reference with respect
to LRU, and holds have an implicit free-on-last unhold semantic whereas
vm_page_unwire() callers must explicitly determine whether to free the
page once the last reference to the page is released.

This change removes the KPIs which directly manipulate hold_count.
Functions such as vm_fault_quick_hold_pages() now return wired pages
instead. Since r328977 the overhead of maintaining LRU for wired pages
is lower, and in many cases vm_fault_quick_hold_pages() callers would
swap holds for wirings on the returned pages anyway, so with this change
we remove a number of page lock acquisitions.

No functional change is intended. __FreeBSD_version is bumped.

Reviewed by: alc, kib
Discussed with: jeff
Discussed with: jhb, np (cxgbe)
Tested by: pho (previous version)
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D19247

Modernize the use of vm_page_unwire(). Since r288122, vm_page_unwire()
has returned TRUE when the wire count transitions to zero, eliminating
the need for callers to inspect the page's wire count.

MFC after: 1 week

Remove unneeded include of vm_phys.h.

ARM: Use new ARMv6 naming conventions for cache and TLB functions
in all but ARMv4 specific files.
Expand ARMv6 compatibility stubs in cpu-v4.h. Use physical address
in L2 cache functions if ARM_L2_PIPT is defined.

Fix slots DMA memory handling. It's similar to r290553.

Discussed with: gonzo
Approved by: kib (mentor)

Fix pagelist bus_dmamap_t map handling. Memory for pagelist is allocated
by bus_dmamem_alloc() which creates associated bus_dmamap_t map for us.
When this memory is freed by bus_dmamem_free(), the map is freed as well.

Thus there is no need to free it explicitly by bus_dmamap_destroy(),
which leads to double freeing.

Discussed with: gonzo
Approved by: kib (mentor)

Fix cache issues with bulk transfers

- Use pmap_quick_enter_page/pmap_quick_remove_page to bounce non-cacheline
aligned head and tail fragments
- Switch from static fragment size to configurable one, newer firmware
passes cache line size as cache_line_size DTB parameter.

With these changes both RPi and RPi2 pass functinal part of vchiq_test

Synchronize with latest upstream VCHI code:

- Add LIB_VERSION ioctl
- Add CLOSE_DELIVERED ioctl
- Bump code version

Upstream version: 3782f2ad42c08f4d32f64138f8be7341afc380f5

Fix BULK read transfer if destination buffer is not cache line-aligned.

We can't use copyout because destination memory is userland address
in another process but we have reference to respective page so map
the page into kernel address space and copy fragments there

- Perform bus_dmamap_sync on pagelist structure
- Wire pages of bulk transfer buffer when preparing pagelist

Remove unused variables

Import VCHI driver for Broadcom's VideoCore IV GPU

Differential Revision: D1753