fix xfs by making I/O to vmap/vmalloc areas work

Here's version two of the patch set.  It actually compiles on both x86
and parisc.  I could do with someone to test it on arm and sh.

The key test is how xfs behaves.  What I did to recreate the problem
on parisc was simply create an 8GB xfs filesystem, use cp -a to pump
about a GB of data into it from my git trees, then unmount and run
xfs_check.  Before the patches, xfs_check reports the whole fs to be
corrupt.  After the patches it reports everything to be OK.

James

---

 arch/arm/include/asm/cacheflush.h    |   10 ++++++++++
 arch/parisc/include/asm/cacheflush.h |    8 ++++++++
 arch/sh/include/asm/cacheflush.h     |    8 ++++++++
 fs/bio.c                             |   19 +++++++++++++++++--
 fs/xfs/linux-2.6/xfs_buf.c           |   10 ++++++++++
 include/linux/highmem.h              |    6 ++++++
 6 files changed, 59 insertions(+), 2 deletions(-)