[RFC/PATCH 1/1] ARM: Handle user space mapped pages in flush_kernel_dcache_page

[Catalin Marinas]

On Mon, May 28, 2012 at 06:35:59AM +0100, Simon Baatz wrote:
> On Mon, May 28, 2012 at 12:32:44PM +0800, Catalin Marinas wrote:
> > On Mon, May 28, 2012 at 12:11:58AM +0100, Simon Baatz wrote:
> > ...
> > > +void __flush_kernel_dcache_page(struct page *page)
> > > +{
> > > +	struct address_space *mapping;
> > > +
> > > +	mapping = page_mapping(page);
> > > +
> > > +	if (!mapping || mapping_mapped(mapping))
> > > +		__cpuc_flush_dcache_area(page_address(page), PAGE_SIZE);
> > > +}
> > > +EXPORT_SYMBOL(__flush_kernel_dcache_page);
> > 
> > I wonder whether the above condition isn't always true after
> > get_user_pages().
> 
> Not sure about corner cases, but I would assume that yes, this is the
> case.  However, the block layer sees the pages from get_user_pages()
> directly only in the O_DIRECT case.  Usually (read fault for page
> cache), flush_kernel_dcache_page() gets pages with mapping != NULL
> and mapping_mapped() == NULL (i.e. no user space mapping (yet)).

And we can probably assume that this is only for new pages with the
PG_dcache_clean bit already cleared (i.e. no need to set it again in
flush_kernel_dcache_page for the lazy case).

-- 
Catalin