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Subject: Re: [PATCH v2 0/2] mm,fork,security: introduce MADV_WIPEONFORK
From: Rik van Riel <riel@redhat.com>
To: Mike Kravetz <mike.kravetz@oracle.com>,
        Florian Weimer <fweimer@redhat.com>, linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, colm@allcosts.net, akpm@linux-foundation.org,
        keescook@chromium.org, luto@amacapital.net, wad@chromium.org,
        mingo@kernel.org, kirill@shutemov.name, dave.hansen@intel.com
Date: Tue, 08 Aug 2017 11:46:08 -0400
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On Tue, 2017-08-08 at 08:19 -0700, Mike Kravetz wrote:

> The other question I was trying to bring up is "What does
> MADV_WIPEONFORK
> mean for various types of mappings?"  For example, if we allow
> MADV_WIPEONFORK on a file backed mapping what does that mapping look
> like in the child after fork?  Does it have any connection at all to
> the
> file?  Or, do we drop all references to the file and essentially
> transform
> it to a private (or shared?) anonymous mapping after fork.  What
> about
> System V shared memory?  What about hugetlb?

My current patch turns any file-backed VMA into an empty
anonymous VMA if MADV_WIPEONFORK was used on that VMA.

> If the use case is fairly specific, then perhaps it makes sense to
> make MADV_WIPEONFORK not applicable (EINVAL) for mappings where the
> result is 'questionable'.

That would be a question for Florian and Colm.

If they are OK with MADV_WIPEONFORK only working on
anonymous VMAs (no file mapping), that certainly could
be implemented.

On the other hand, I am not sure that introducing cases
where MADV_WIPEONFORK does not implement wipe-on-fork
semantics would reduce user confusion...