Re: [PATCH v1] hugetlbfs: don't access uninitialized memmaps in pfn_range_valid_gigantic()

From: Mike Kravetz
Date: Tue Oct 15 2019 - 14:34:29 EST

On 10/15/19 5:07 AM, David Hildenbrand wrote:
> 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]
> Reported-by: Michal Hocko <mhocko@xxxxxxxxxx>
> Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319
> Cc: stable@xxxxxxxxxxxxxxx # v4.13+
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

Thanks David,

Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>

Mike Kravetz