netdev - Re: [RFC][PATCHES] iov

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Date:	Mon, 8 Dec 2014 19:28:17 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [RFC][PATCHES] iov_iter.c rewrite

On Mon, Dec 08, 2014 at 10:57:31AM -0800, Linus Torvalds wrote:
> So the whole "get_page()" thing is broken. Iterating over pages in a
> KVEC is simply wrong, wrong, wrong. It needs to fail.

Well, _that_ is easy to do, of course...  E.g. by replacing that thing in
iov_iter_get_pages()/iov_iter_get_pages_alloc() with ({ return -EFAULT; })
will do it.

> Iterating over a KVEC to *copy* data is ok. But no page lookup stuff
> or page reference things.
> 
> The old code that apparently used "get_user_pages_fast()" was ok
> almost by mistake, because it fails on all kernel pages.

On x86 it does, but I don't see anything obvious in generic version in
mm/gup.c, so the old code might still have a problem on some architectures.
What am I missing here?
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