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    SubjectRe: [PATCH 5/5] tun: vringfd xmit support.
    On Sat, 19 Apr 2008 01:15:15 +1000 Rusty Russell <rusty@rustcorp.com.au> wrote:

    > >
    > > What is the maximum numbet of pages which an unpriviliged user can
    > > concurrently pin with this code?
    >
    > Since only root can open the tun device, it's currently OK. The old code
    > kmalloced and copied: is there some mm-fu reason why pinning userspace memory
    > is worse?

    We generally try to avoid it - it allows users to dos the box. Although I
    suspect that direct-io presently permits users to transiently pin an amount
    of memory which is proportional to the number of disks upon which they can
    open files.

    > Subject: Export release_pages; nice undo for get_user_pages.
    >
    > Andrew Morton suggests tun/tap use release_pages, but it's not
    > exported. It's not clear to me why this is in swap.c, but it exists
    > even without CONFIG_SWAP, so that's OK.
    >
    > Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
    >
    > diff -r abd2ad431e5c mm/swap.c
    > --- a/mm/swap.c Sat Apr 19 00:34:54 2008 +1000
    > +++ b/mm/swap.c Sat Apr 19 01:11:40 2008 +1000
    > @@ -346,6 +346,7 @@ void release_pages(struct page **pages,
    >
    > pagevec_free(&pages_to_free);
    > }
    > +EXPORT_SYMBOL(release_pages);
    >
    > /*
    > * The pages which we're about to release may be in the deferred lru-addition

    acked-by: me.


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