Curiously, the Crypto API scatterwalk incremented pages by hand
rather than using nth_page. Possibly because scatterwalk predates
nth_page (the following commit is from the history tree):
commit 3957f2b34960d85b63e814262a8be7d5ad91444d
Author: James Morris <jmorris@intercode.com.au>
Date: Sun Feb 2 07:35:32 2003 -0800
[CRYPTO]: in/out scatterlist support for ciphers.
Fix this by using nth_page.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
e9ed7aff25