powerpc/mm: Code cleanup for __hash_page_thp

This part was commented from commit 6d492ecc6489
("powerpc/THP: Add code to handle HPTE faults for hugepages")
in about 11 years before.

If there are no plans to enable this part code in the future,
we can remove this dead code and replace with a comment
explaining what the dead code was trying to say.

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Suggested-by: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240301085834.1512921-1-chentao@kylinos.cn

powerpc/book3s64/kuap: Use Key 3 for kernel mapping with hash translation

This patch updates kernel hash page table entries to use storage key 3
for its mapping. This implies all kernel access will now use key 3 to
control READ/WRITE. The patch also prevents the allocation of key 3 from
userspace and UAMOR value is updated such that userspace cannot modify key 3.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Reviewed-by: Sandipan Das <sandipan@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201127044424.40686-9-aneesh.kumar@linux.ibm.com

powerpc/mm: Move book3s64 specifics in subdirectory mm/book3s64

Many files in arch/powerpc/mm are only for book3S64. This patch
creates a subdirectory for them.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
[mpe: Update the selftest sym links, shorten new filenames, cleanup some
whitespace and formatting in the new files.]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>