[PATCH V4] ARM: handle user space mapped pages in flush_kernel_dcache_page

[Simon Baatz]

On Fri, May 31, 2013 at 05:07:22PM +0800, Ming Lei wrote:
> On Sun, May 12, 2013 at 1:35 PM, Simon Baatz <gmbnomis at gmail.com> wrote:
> > +void flush_kernel_dcache_page(struct page *page)
> > +{
> > +       if (cache_is_vivt() || cache_is_vipt_aliasing()) {
> > +               struct address_space *mapping;
> > +
> > +               mapping = page_mapping(page);
> > +
> > +               if (!mapping || mapping_mapped(mapping))
> 
> It is better to replace mapping_mapped(mapping) with page_mapped(page).

Good point. I did not have the time to look into your proposed change
for flush_dcache_page() yet.

However, this patch here is a fix for a long standing bug, which
should also be applied to stable in one form or another.  I would not
like to mix it with a separate performance improvement.

But, of course, if we decide to change the respective condition in
flush_dcache_page(), we should also change it in
flush_kernel_dcache_page() at the same time (provided this patch gets
accepted).
 
> > +                       __flush_kernel_dcache_page(page);
> 
> I am wondering if I-cache should be flushed here since the user mapping
> on the page may be executable and I/D coherency should be maintained.

Me too. In fact, I wondered so much that I proposed it myself in a
previous version of the patch (see [1]) :-) However, this has never
been part of flush_kernel_dcache_page() and it is not clear whether
the flush for I/D-cache coherency is really needed here (or in
flush_dcache_page() for that matter) or whether it is sufficient to
do it when mapping the page into user space.

On top of that neither Russell nor Catalin liked this idea very much.

- Simon


[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2012-October/124292.html