In preparation for the second patch, abstract away the THP allocation
logic present in the create_huge_pmd() path, which corresponds to the
faulting case when no page is present.

There should be no functional change as a result of applying this patch,
except that, as David notes at [1], a PMD-aligned address should
be passed to update_mmu_cache_pmd().

[1]: https://lore.kernel.org/all/ddd3fcd2-48b3-4170-bcaa-2fe66e093f43@redhat.com/ (local)

Acked-by: David Hildenbrand <redacted>
Reviewed-by: Kefeng Wang <redacted>
Signed-off-by: Dev Jain <dev.jain@arm.com>
---
  mm/huge_memory.c | 98 ++++++++++++++++++++++++++++--------------------
  1 file changed, 57 insertions(+), 41 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 4e34b7f89daf..e3bcdbc9baa2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c

@@ -1148,47 +1148,81 @@ unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
  }
  EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
  
-static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
-			struct page *page, gfp_t gfp)
+static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
+					      unsigned long addr)