Re: [PATCH v3 3/3] powerpc/8xx: Implement support of hugepages

Christophe Leroy [off-list ref] writes:

8xx uses a two level page table with two different linux page size
support (4k and 16k). 8xx also support two different hugepage sizes
512k and 8M. In order to support them on linux we define two different
page table layout.

The size of pages is in the PGD entry, using PS field (bits 28-29):
00 : Small pages (4k or 16k)
01 : 512k pages
10 : reserved
11 : 8M pages

For 512K hugepage size a pgd entry have the below format
[<hugepte address >0101] . The hugepte table allocated will contain 8
entries pointing to 512K huge pte in 4k pages mode and 64 entries in
16k pages mode.

For 8M in 16k mode, a pgd entry have the below format
[<hugepte address >1101] . The hugepte table allocated will contain 8
entries pointing to 8M huge pte.

For 8M in 4k mode, multiple pgd entries point to the same hugepte
address and pgd entry will have the below format
[<hugepte address>1101]. The hugepte table allocated will only have one
entry.

For the time being, we do not support CPU15 ERRATA when HUGETLB is
selected

For the generic bits
Reviewed-by: Aneesh Kumar K.V <redacted>

Signed-off-by: Christophe Leroy <redacted>
---
v2: This v1 was split in two parts. This part focuses on adding the
support on 8xx. It also fixes an error in TLBmiss handlers in the
case of 8M hugepages in 16k pages mode.

-aneesh