From: David Hildenbrand <david@xxxxxxxxxx> Subject: hugetlbfs: don't access uninitialized memmaps in pfn_range_valid_gigantic() Uninitialized memmaps contain garbage and in the worst case trigger kernel BUGs, especially with CONFIG_PAGE_POISONING. They should not get touched. Let's make sure that we only consider online memory (managed by the buddy) that has initialized memmaps. ZONE_DEVICE is not applicable. page_zone() will call page_to_nid(), which will trigger VM_BUG_ON_PGFLAGS(PagePoisoned(page), page) with CONFIG_PAGE_POISONING and CONFIG_DEBUG_VM_PGFLAGS when called on uninitialized memmaps. This can be the case when an offline memory block (e.g., never onlined) is spanned by a zone. Note: As explained by Michal in [1], alloc_contig_range() will verify the range. So it boils down to the wrong access in this function. [1] http://lkml.kernel.org/r/20180423000943.GO17484@xxxxxxxxxxxxxx Link: http://lkml.kernel.org/r/20191015120717.4858-1-david@xxxxxxxxxx Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") [visible after d0dc12e86b319] Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Reported-by: Michal Hocko <mhocko@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> [4.13+] Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/hugetlb.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) --- a/mm/hugetlb.c~hugetlbfs-dont-access-uninitialized-memmaps-in-pfn_range_valid_gigantic +++ a/mm/hugetlb.c @@ -1084,11 +1084,10 @@ static bool pfn_range_valid_gigantic(str struct page *page; for (i = start_pfn; i < end_pfn; i++) { - if (!pfn_valid(i)) + page = pfn_to_online_page(i); + if (!page) return false; - page = pfn_to_page(i); - if (page_zone(page) != z) return false; _
