Viewing page tables and some other questions regarding the MMU

Russell King - ARM Linux linux at
Tue Apr 6 13:36:00 EDT 2010

On Tue, Apr 06, 2010 at 06:59:01PM +0200, Leo Barnes wrote:
> (As a side note, the reason I am investigating this is because I read
> somewhere in an ARM reference manual that having multiple maps to the
> same physical region with differing memory attributes is illegal, but
> ioremap_cached obviously manages it somehow.)

ioremap_cached doesn't "manage it" - it doesn't prevent setting up
illegal conditions.  That's the responsibility of the programmer to
ensure that the architecture restrictions aren't violated.

So, the kernel will allow you to create a strongly ordered mapping
and a cached mapping of the same physical space without complaint;
if this is not permitted by the architecture, then you must not ask
the kernel to create this illegal condition.

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