mm: add generic flush_icache_pages() and documentation

	This is used primarily during fault processing.

5) ``void update_mmu_cache(struct vm_area_struct *vma,

   unsigned long address, pte_t *ptep)``

5) ``void update_mmu_cache_range(struct vm_fault *vmf,

   struct vm_area_struct *vma, unsigned long address, pte_t *ptep,

   unsigned int nr)``

	At the end of every page fault, this routine is invoked to

	tell the architecture specific code that a translation

	now exists at virtual address "address" for address space

	"vma->vm_mm", in the software page tables.

	At the end of every page fault, this routine is invoked to tell

	the architecture specific code that translations now exists

	in the software page tables for address space "vma->vm_mm"

	at virtual address "address" for "nr" consecutive pages.

	This routine is also invoked in various other places which pass

	a NULL "vmf".

	A port may use this information in any way it so chooses.

	For example, it could use this event to pre-load TLB

	private".  The kernel guarantees that, for pagecache pages, it will

	clear this bit when such a page first enters the pagecache.

	This allows these interfaces to be implemented much more efficiently.

	It allows one to "defer" (perhaps indefinitely) the actual flush if

	there are currently no user processes mapping this page.  See sparc64's

	flush_dcache_page and update_mmu_cache implementations for an example

	of how to go about doing this.

	This allows these interfaces to be implemented much more

	efficiently.  It allows one to "defer" (perhaps indefinitely) the

	actual flush if there are currently no user processes mapping this

	page.  See sparc64's flush_dcache_page and update_mmu_cache_range

	implementations for an example of how to go about doing this.

	The idea is, first at flush_dcache_page() time, if page_file_mapping()

	returns a mapping, and mapping_mapped on that mapping returns %false,

	just mark the architecture private page flag bit.  Later, in

	update_mmu_cache(), a check is made of this flag bit, and if set the

	flush is done and the flag bit is cleared.

	The idea is, first at flush_dcache_page() time, if

	page_file_mapping() returns a mapping, and mapping_mapped on that

	mapping returns %false, just mark the architecture private page

	flag bit.  Later, in update_mmu_cache_range(), a check is made

	of this flag bit, and if set the flush is done and the flag bit

	is cleared.

	.. important::

  ``void flush_icache_page(struct vm_area_struct *vma, struct page *page)``

	All the functionality of flush_icache_page can be implemented in

	flush_dcache_page and update_mmu_cache. In the future, the hope

	flush_dcache_page and update_mmu_cache_range. In the future, the hope

	is to remove this interface completely.

The final category of APIs is for I/O to deliberately aliased address

#endif

#ifndef flush_icache_page

static inline void flush_icache_pages(struct vm_area_struct *vma,

				     struct page *page, unsigned int nr)

{

}

static inline void flush_icache_page(struct vm_area_struct *vma,

				     struct page *page)

{