mm/hugetlb: initialize gigantic bootmem hugepage struct pages earlier

In the Linux kernel, the following vulnerability has been resolved:

mm/hugetlb: initialize gigantic bootmem hugepage struct pages earlier

Gigantic bootmem HugeTLB pages are currently initialized from
hugetlb_init(), but page_alloc_init_late() runs earlier and walks
pageblocks to determine zone contiguity.

If a bootmem HugeTLB region is marked noinit, set_zone_contiguous() can
observe still-uninitialized struct pages through
__pageblock_pfn_to_page(). This may not trigger an immediate failure, but
it can make set_zone_contiguous() compute the wrong zone contiguity state.
If extra poisoned-page checks are added in this path, such as
PF_POISONED_CHECK() in page_zone_id(), it can also trigger an early boot
panic.

Initialize gigantic bootmem HugeTLB struct pages from
page_alloc_init_late(), before zone contiguity is evaluated, so later page
allocator setup only sees valid struct page state. This also makes the
initialization order more natural, as struct pages should be initialized
before later code inspects them.