Linux: 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.