The patch below changes access_process_vm to use a new architecture
hook, flush_icache_user_range, instead of flush_icache_page, and adds
a definition of flush_icache_user_range which does the same thing as
flush_icache_page for all architectures except PPC.  (The PPC update
that is in Linus' BK tree already includes a suitable definition of
flush_icache_user_range.)

The reason for doing this is that when flush_icache_page is called
from do_no_page or do_swap_page, I want to be able to do the flush
conditionally, based on the state of the page.  In contrast,
access_process_vm needs to do the flush unconditionally since it has
just modified the page.  In the access_process_vm case it is useful to
have the information about the user address and length that have been
modified since then we can just flush the affected cache lines rather
than the whole page.

This patch should make it easy to improve performance on alpha, since
there (as I understand it) the icache flush is not needed at all in
do_no_page or do_swap_page, but is needed in access_process_vm.  All
that is needed is to make flush_icache_page a noop on alpha.  The
patch below doesn't do this, I'll let the alpha maintainers push that
change if they want.