shared memory problem on ARM v5TE using threads

[Pavel Machek]

On Sun 2009-12-13 12:00:33, Russell King - ARM Linux wrote:
> On Sun, Dec 13, 2009 at 01:48:48PM +0200, Ronen Shitrit wrote:
> > Another idea is to change the shared mapping handling, in case of vivt with pipt L2, so it won't remap the shared area as non-cacheable:
> > - make_coherent won't use adjust_pte and leave only the regular flush.
> > - Flush L1 for all context switches, also for the case that the new process is using same mm (thread context switch).
> 
> That doesn't work.
> 
> Well, with a VIVT L1, we flush the L1 on all MM switches anyway.
> Flushing it on any thread switch is not going to help that much.
> 
> The problem with shared mmaps is that if you have multiple within the
> same thread, it is required that they are _all_ coherent with respect
> to each other, whether or not a context switch has occurred.

But that's pretty unusual situation, right?

So what about...

a) flush L2 on context switch

b) disable L2 when thread has maps one physical address twice



-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html