arm_syscall cacheflush breakage on VIPT platforms

[Russell King - ARM Linux]

On Mon, Sep 28, 2009 at 02:19:26PM +0100, Jamie Lokier wrote:
> Aieee.  Is sys_cacheflush architecturally the Right Way to do DMA to
> userspace, or is it just luck that it happens to work?
> 
> Does that include O_DIRECT regular file I/O as used by databases on
> these ARMs?  (Nobody ever gives a straight answer)

Most definitely not.  As far as O_DIRECT goes, I've no idea what to do
about that, or even if it's a problem.  I just don't use it so it's
not something I care about.

I wouldn't even know _how_ to use it or even how to provoke any bugs
in that area.