Re: [PATCH 5/7] powerpc: Swizzle around 4K PTE bits to free up bit 5 and bit 6

On Thu, Sep 14, 2017 at 11:48:34AM +1000, Balbir Singh wrote:

On Fri,  8 Sep 2017 15:44:45 -0700
Ram Pai [off-list ref] wrote:

quoted

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

Aneesh, i think, is working on moving slot information out of the PTE.
If that happens, we will have leg-space to support more keys.

RP