linux-kernel - Re: [PATCH] mm: check VMA flags to avoid invalid PROT

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Date:   Mon, 10 Oct 2016 09:28:28 +0100
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Hugh Dickins <hughd@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Rik van Riel <riel@...hat.com>,
        linux-mm <linux-mm@...ck.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        tbsaunde@...aunde.org, robert@...llahan.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: check VMA flags to avoid invalid PROT_NONE NUMA
 balancing

On Mon, Oct 10, 2016 at 09:47:12AM +0200, Jan Kara wrote:
> Yeah, so my cleanups where mostly concerned about mmap_sem locking and
> reducing number of places which cared about those. Regarding flags for
> get_user_pages() / get_vaddr_frames(), I agree that using flags argument
> as Linus suggests will make it easier to see what the callers actually
> want. So I'm for that.

Great, thanks Jan! I have a draft patch that needs a little tweaking/further
testing but isn't too far off.

One thing I am wondering about is whether functions that have write/force
parameters replaced with gup_flags should mask against (FOLL_WRITE | FOLL_FORCE)
to prevent callers from doing unexpected things with other FOLL_* flags?

I'm inclined _not_ to because it adds a rather non-obvious restriction on this
parameter, reduces clarity about which flags are actually being used (which is
the point of the patch in the first place), and the caller ought to know what
they are doing.

I'd be curious to hear people's thoughts on this.