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Date: Mon, 22 Feb 2016 09:43:34 +1100
From: Paul Mackerras <paulus@ozlabs.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Paul Mackerras via Linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [RFC PATCH 2/9] powerpc/mm/book3s-64: Free up 7 high-order bits
 in the Linux PTE
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On Sat, Feb 20, 2016 at 09:46:19PM +0530, Aneesh Kumar K.V wrote:
> Paul Mackerras <paulus@samba.org> writes:
> 
> > This frees up bits 57-63 in the Linux PTE on 64-bit Book 3S machines.
> > In the 4k page case, this is done just by reducing the size of the
> > RPN field to 39 bits, giving 51-bit real addresses.  In the 64k page
> > case, we had 10 unused bits in the middle of the PTE, so this moves
> > the RPN field down 10 bits to make use of those unused bits.  This
> > means the RPN field is now 3 bits larger at 37 bits, giving 53-bit
> > real addresses in the normal case, or 49-bit real addresses for the
> > special 4k PFN case.
> 
> 
> Is it ok to have different real address bits between 4k and 64k linux
> config ?

Do you mean a different number of address bits, or a different
location?  In fact both were different before this patch anyway.

Paul.