[PATCH 4/4] powerpc: Add vm debug code to catch errors

[Paul Mackerras]

On Thu, Feb 14, 2013 at 02:06:23PM +0530, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar at linux.vnet.ibm.com>
> 
> We need to make sure that we don't have higher bits of kernel effective
> address set. That would result in multiple kernel segments having same
> proto vsid. Add debug code to make sure we capture this.

I'm not sure that WARN_ON is the best way to handle this, since this
code is called from low levels of the MMU management code, and a
WARN_ON will cause a trap that could possibly come at a time when we
can't handle a trap very well.  I think instead these functions should
return a vsid of 0 for bad addresses, and the callers should detect
that case and handle it appropriately, e.g. hash_page() should return
an error.

Paul.