[RFC 10/11] ARM: arrange for flush_cache_range() to always flush the I-cache

[Russell King - ARM Linux]

On Wed, Oct 28, 2009 at 03:51:38PM +0000, Catalin Marinas wrote:
> On Sun, 2009-10-25 at 14:12 +0000, Russell King wrote:
> > Dirk Behme reported instability on ARM11 SMP (VIPT non-aliasing cache)
> > caused by the dynamic linker changing protection on text pages to write
> > GOT entries.  The problem is due to an interaction between the write
> > faulting code providing new anonymous pages (which haven't had their
> > I-cache cleaned due to no VM_EXEC) and change_protection() not doing
> > any kind of I-cache maintainence.
> > 
> > Work around this by flushing the I-cache in flush_cache_range() for
> > VM_EXEC VMAs (which is what we have when the region is being made
> > executable again.)  This ensures that the I-cache will be up to date
> > with the new COW'd pages.
> 
> Are you sure this fixes the problem? IIRC this is mainly caused by the
> write-allocate D-cache and that copy_to_user_highpage() doesn't flush
> the D-cache. Just an I-cache invalidation wouldn't help much.

Not on its own (sorry, should've made that clear).  I'm not entirely
sure what's happening with the other half of the fix (the thread seemed
to die before reaching any kind of conclusion) but this is the right
solution for the I-cache side of the problem.