Re: [RFC v2 02/12] powerpc: Free up four 64K PTE bits in 64K backed hpte pages.

From: Anshuman Khandual
Date: Tue Jun 20 2017 - 06:52:56 EST

On 06/17/2017 09:22 AM, Ram Pai wrote:
> Rearrange 64K PTE bits to free up bits 3, 4, 5 and 6
> in the 64K backed hpte pages. This along with the earlier
> patch will entirely free up the four bits from 64K PTE.
> This patch does the following change to 64K PTE that is
> backed by 64K hpte.
> H_PAGE_F_SECOND which occupied bit 4 moves to the second part
> of the pte.
> H_PAGE_F_GIX which occupied bit 5, 6 and 7 also moves to the
> second part of the pte.
> since bit 7 is now freed up, we move H_PAGE_BUSY from bit 9
> to bit 7. Trying to minimize gaps so that contiguous bits
> can be allocated if needed in the future.
> The second part of the PTE will hold
> (H_PAGE_F_SECOND|H_PAGE_F_GIX) at bit 60,61,62,63.

I still dont understand how we freed up the 5th bit which is
used in the 5th patch. Was that bit never used for any thing
on 64K page size (64K and 4K mappings) ?

+#define _RPAGE_RSV5 0x00040UL