[PATCH] powerpc/mm: add devmem_is_allowed() for STRICT_DEVMEM checking

[Scott Wood]

On Tue, 14 Jun 2011 14:17:01 -0400
Steve Best <sfbest at us.ibm.com> wrote:

> On Tue, 2011-06-14 at 12:30 -0500, Nathan Lynch wrote:
> > Hi Steve,
> > 
> > On Tue, 2011-06-14 at 12:58 -0400, Steve Best wrote:
> > > +/*
> > > + * devmem_is_allowed() checks to see if /dev/mem access to a certain address
> > > + * is valid. The argument is a physical page number.
> > > + *
> > > + * On PowerPC, access has to be given to data regions used by X. We have to
> > > + * disallow access to device-exclusive MMIO regions and system RAM. 
> > > + */
> > > +int devmem_is_allowed(unsigned long pfn)
> > > +{
> > > +        if ((pfn >= 57360 || pfn <= 57392))
> > > +                return 1;
> > 
> > That seems... fragile.  Where do these numbers come from, and are they
> > appropriate for all platforms and configurations?
> 
> This is the range I got from testing pseries blades and servers. maybe
> there is a better way to get this range anyone know of a way?

Use iomem_is_exclusive(), as other architectures (e.g. x86, arm) do.

Anything else is both platform-specific, and inappropriate hardcoding of
policy.

-Scott