Add VM_BUG_ON bounds checks to ensure the newly lifted and created page
memory operations do not result in corrupted data in neighbor pages.[1][2]

[1] https://lore.kernel.org/lkml/20201210053502.GS1563847@iweiny-DESK2.sc.intel.com/
[2] https://lore.kernel.org/lkml/20210209110931.00f00e47d9a0529fcee2ff01@linux-foundation.org/Suggested-by: NMatthew Wilcox <willy@infradead.org>
Suggested-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NIra Weiny <ira.weiny@intel.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>