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Date: Thu, 14 Sep 2017 11:48:34 +1000
From: Balbir Singh <bsingharora@gmail.com>
To: Ram Pai <linuxram@us.ibm.com>
Cc: mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org,
 benh@kernel.crashing.org, paulus@samba.org, khandual@linux.vnet.ibm.com,
 aneesh.kumar@linux.vnet.ibm.com, hbabu@us.ibm.com, mhocko@kernel.org,
 bauerman@linux.vnet.ibm.com, ebiederm@xmission.com
Subject: Re: [PATCH 5/7] powerpc: Swizzle around 4K PTE bits to free up bit
 5 and bit 6
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On Fri,  8 Sep 2017 15:44:45 -0700
Ram Pai <linuxram@us.ibm.com> wrote:

> We  need  PTE bits  3 ,4, 5, 6 and 57 to support protection-keys,
> because these are  the bits we want to consolidate on across all
> configuration to support protection keys.
> 
> Bit 3,4,5 and 6 are currently used on 4K-pte kernels.  But bit 9
> and 10 are available.  Hence  we  use the two available bits and
> free up bit 5 and 6.  We will still not be able to free up bit 3
> and 4. In the absence  of  any  other free bits, we will have to
> stay satisfied  with  what we have :-(.   This means we will not
> be  able  to support  32  protection  keys, but only 8.  The bit
> numbers are  big-endian as defined in the  ISA3.0
>

Any chance for 4k PTE's we can do slot searching for the PTE?
I guess thats add additional complexity

Balbir Singh.