Convert x86 pgd_lists to ptdescs

This continues the ptdesc conversions for x86[1]. This is a necessary step
in preparation for the separate allocation of ptdescs from struct page.
Once ptdescs are not wrappers, the pgd_list should be used to find our
ptdesc, not page.

In fact, after patch 4 we can successfully boot a 32-bit x86 kernel
that separately allocates ptdescs.

All of the patches are rather straightforward, I just kept them split up
for ease of review. There are no intended functional changes as ptdescs
are currently still wrappers around struct page.

[1] https://lore.kernel.org/linux-mm/20260211195233.368497-1-...

----------------

I've compiled and booted both 64 and 32 bit on a kernel with separately
allocated ptdescs. I ensured the codepaths were hit for all the changes
except Xen.

This applies cleanly to the tip bot. I'm thinking this can go through
Dave's mm.

Vishal Moola (9):
  x86/mm/pat: Use IS_ENABLED() instead of ifdef
  x86/mm/pat: Convert __set_pmd_pte() to ptdescs
  x86/mm/pat: Convert collapse_pmd_page() to ptdescs
  x86/mm: Convert arch_sync_kernel_mappings() to ptdescs
  x86/mm: Convert sync_global_pgds_l5() to ptdescs
  x86/mm: Convert sync_global_pgds_l4() to ptdescs
  x86/mm: Convert pgd_page_get_mm() to ptdescs
  x86/xen: Convert xen_mm_pin_all() to ptdescs
  x86/xen: Convert xen_mm_unpin_all() to ptdescs

 arch/x86/include/asm/pgtable.h       |  2 +-
 arch/x86/include/asm/pgtable_types.h |  2 +-
 arch/x86/mm/fault.c                  |  8 ++++----
 arch/x86/mm/init_64.c                | 16 ++++++++--------
 arch/x86/mm/pat/set_memory.c         | 17 ++++++++---------
 arch/x86/mm/pgtable.c                |  4 ++--
 arch/x86/xen/mmu_pv.c                | 22 +++++++++++-----------
 7 files changed, 35 insertions(+), 36 deletions(-)

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2.54.0