cryptoapi incorrect struct page usage

["Mika Penttilä" <mika.penttila@kolumbus.fi>]

It seems that cryptoapi usage wrt mm is not safe. At least both ipsec 
and cryptoloop practise these kinds of things :

example from net/xfrm/xfrm_algo.c

int
skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, 
int len)
{
    int start = skb_headlen(skb);
    int i, copy = start - offset;
    int elt = 0;

    if (copy > 0) {
        if (copy > len)
            copy = len;
        sg[elt].page = virt_to_page(skb->data + offset);
        sg[elt].offset = (unsigned long)(skb->data + offset) % PAGE_SIZE;
        sg[elt].length = copy;



so unpinned pages are passed to cryptoapi. Nothing prevents these pages 
from being swapped out. Something like get_user_pages() is needed to pin 
these pages for the duration of crypto operations. Comments?

--Mika