Convert 64-bit x86/mm/pat to ptdescs

x86/mm/pat should be using ptdescs. One line has already been
converted to pagetable_free(), while the allocation sites use
get_free_pages(). This causes issues separately allocating ptdescs
from struct page.

The first patch introduces new ptdesc apis that operate on addresses.
These are like get_free_pages() and free_pages() helper functions.

The remaining patches convert the allocation/free sites to use ptdescs. In
the short term, this helps enable Matthew's work to allocate frozen
pagetables[1]. And in the long term, this will help us cleanly split
ptdesc allocations from struct page[2].

The pgd_list should also be using ptdescs (for 32bit in this file). This
can be done in a different patchset since there's other users of pgd_list
that still need to be converted.

[1] https://lore.kernel.org/linux-mm/20251113140448.1814860-1...
[2] https://lore.kernel.org/linux-mm/20251020001652.2116669-1...

------

Based on current mm-new.

v5:
  - Return a void pointer instead of unsigned long in allocation
  - More imperative voice in commit logs

Vishal Moola (Oracle) (4):
  mm: Add address apis for ptdescs
  x86/mm/pat: Convert pte code to use ptdescs
  x86/mm/pat: Convert pmd code to use ptdescs
  x86/mm/pat: Convert split_large_page() to use ptdescs

 arch/x86/mm/pat/set_memory.c | 49 ++++++++++++++++++------------------
 include/linux/mm.h           |  4 +++
 mm/memory.c                  | 34 +++++++++++++++++++++++++
 3 files changed, 63 insertions(+), 24 deletions(-)

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2.52.0