switch the block layer to use kmap_local_page v3

[Christoph Hellwig]

Hi all,

this series switches the core block layer code and all users of the
existing bvec kmap helpers to use kmap_local_page.  Drivers that
currently use open coded kmap_atomic calls will converted in a follow
on series.

To do so a new kunmap variant is added that calls
flush_kernel_dcache_page.  I'm not entirely sure where to call
flush_dcache_page vs flush_kernel_dcache_page, so I've tried to follow
the documentation here, but additional feedback would be welcome.

Note that the ps3disk has a minir conflict with the
flush_kernel_dcache_page removal in linux-next through the -mm tree.
I had hoped that change would go into 5.14, but it seems like it is
being held for 5.15.

Changes since v2:
 - rely on the flush_dcache_helpers in memcpy_to_page and memzero_page
   that now hit mainline

Changes since v1:
 - add more/better comments
 - add a new kunmap_local_dirty helper to feal with
   flush(_kernel)_dcache_page

Diffstat:
 arch/mips/include/asm/mach-rc32434/rb.h |    2 -
 block/bio-integrity.c                   |   14 +++-----
 block/bio.c                             |   37 ++++++----------------
 block/blk-map.c                         |    2 -
 block/bounce.c                          |   39 +++++-------------------
 block/t10-pi.c                          |   16 +++------
 drivers/block/ps3disk.c                 |   19 +----------
 drivers/block/rbd.c                     |   15 +--------
 drivers/md/dm-writecache.c              |    5 +--
 include/linux/bio.h                     |   42 -------------------------
 include/linux/bvec.h                    |   52 ++++++++++++++++++++++++++++++--
 include/linux/highmem-internal.h        |    7 ++++
 include/linux/highmem.h                 |   10 ++++--
 13 files changed, 102 insertions(+), 158 deletions(-)