kernel - userspace shared memory

[arnd@arndb.de (Arnd Bergmann)]

On Friday 10 June 2011 06:16:42 viresh kumar wrote:
> On 06/06/2011 10:47 PM, Zoltan Devai wrote:
> > Hi all,
> > 
> > We are having a kernel driver and a userspace application that
> > communicates via shared memory. The problem is, that when the userspace
> > application modifies some data in the shared memory, this modification
> > is not "visible" when the kernel driver takes a look at that memory
> > location (specifically this code is in a kernel timer function).
> > Actually, the modification is sometimes seen, sometimes not,
> > which suggests that we are having some kind of cache coherency issue.
> > The strange thing is, that AFAIK we have disabled caching on the pages
> > where the shared memory resides.
> 
> Which core are you using? One problem that i am aware of is, on ARMv7
> "Multiple mappings of memory with different attributes is not supported".
> And the result of such is unspecified.

There are also possible problems with cache aliases. Zoltan, if this is
an out-of-tree driver, please post it here in patch form if you want
anyone to give you a more specific answer.

	Arnd