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SubjectRe: [RFC v6 02/62] powerpc: Free up four 64K PTE bits in 64K backed HPTE pages
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Ram Pai <linuxram@us.ibm.com> writes:

> 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.
> The bit numbers are big-endian as defined in the ISA3.0
>
> This patch does the following change to 64K PTE backed
> by 64K HPTE.
>
> H_PAGE_F_SECOND (S) which occupied bit 4 moves to the
> second part of the pte to bit 60.
> H_PAGE_F_GIX (G,I,X) which occupied bit 5, 6 and 7 also
> moves to the second part of the pte to bit 61,
> 62, 63, 64 respectively
>
> since bit 7 is now freed up, we move H_PAGE_BUSY (B) from
> bit 9 to bit 7.
>
> The second part of the PTE will hold
> (H_PAGE_F_SECOND|H_PAGE_F_GIX) at bit 60,61,62,63.
> NOTE: None of the bits in the secondary PTE were not used
> by 64k-HPTE backed PTE.
>
> Before the patch, the 64K HPTE backed 64k PTE format was
> as follows
>
> 0 1 2 3 4 5 6 7 8 9 10...........................63
> : : : : : : : : : : : :
> v v v v v v v v v v v v
>
> ,-,-,-,-,--,--,--,--,-,-,-,-,-,------------------,-,-,-,
> |x|x|x| |S |G |I |X |x|B| |x|x|................|x|x|x|x| <- primary pte
> '_'_'_'_'__'__'__'__'_'_'_'_'_'________________'_'_'_'_'
> | | | | | | | | | | | | |..................| | | | | <- secondary pte
> '_'_'_'_'__'__'__'__'_'_'_'_'__________________'_'_'_'_'
>
> After the patch, the 64k HPTE backed 64k PTE format is
> as follows
>
> 0 1 2 3 4 5 6 7 8 9 10...........................63
> : : : : : : : : : : : :
> v v v v v v v v v v v v
>
> ,-,-,-,-,--,--,--,--,-,-,-,-,-,------------------,-,-,-,
> |x|x|x| | | | |B |x| | |x|x|................|.|.|.|.| <- primary pte
> '_'_'_'_'__'__'__'__'_'_'_'_'_'________________'_'_'_'_'
> | | | | | | | | | | | | |..................|S|G|I|X| <- secondary pte
> '_'_'_'_'__'__'__'__'_'_'_'_'__________________'_'_'_'_'
>
> The above PTE changes is applicable to hugetlbpages aswell.
>
> The patch does the following code changes:
>
> a) moves the H_PAGE_F_SECOND and H_PAGE_F_GIX to 4k PTE
> header since it is no more needed b the 64k PTEs.
> b) abstracts out __real_pte() and __rpte_to_hidx() so the
> caller need not know the bit location of the slot.
> c) moves the slot bits the secondary pte.
>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
With changes suggested for the first patch.

> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> ---


-aneesh

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