linux-kernel - Re: interaction of MADV_PAGEOUT with CoW anonymous mappings?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200312001849.GA96953@google.com>
Date:   Wed, 11 Mar 2020 17:18:49 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Jann Horn <jannh@...gle.com>, Linux-MM <linux-mm@...ck.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Daniel Colascione <dancol@...gle.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>
Subject: Re: interaction of MADV_PAGEOUT with CoW anonymous mappings?

On Wed, Mar 11, 2020 at 04:53:17PM -0700, Shakeel Butt wrote:
> On Wed, Mar 11, 2020 at 1:45 AM Michal Hocko <mhocko@...nel.org> wrote:
> >
> > On Tue 10-03-20 15:48:31, Dave Hansen wrote:
> > > Maybe instead of just punting on MADV_PAGEOUT for map_count>1 we should
> > > only let it affect the *local* process.  We could still put the page in
> > > the swap cache, we just wouldn't go do the rmap walk.
> >
> > Is it really worth medling with the reclaim code and special case
> > MADV_PAGEOUT there? I mean it is quite reasonable to have an initial
> > implementation that doesn't really touch shared pages because that can
> > lead to all sorts of hard to debug and unexpected problems. So I would
> > much rather go with a simple patch to check map count first and see
> > whether somebody actually cares about those shared pages and go from
> > there.
> >
> > Minchan, do you want to take my diff and turn it into the proper patch
> > or should I do it.
> >
> 
> What about the remote_madvise(MADV_PAGEOUT)? Will your patch disable
> the pageout from that code path as well for pages with mapcount > 1?

Maybe, not because process_madvise syscall needs more previliedge(ie,
PTRACE_MODE_ATTACH_FSCREDS) so I guess it would be more secure.
So in that case, I want to rely on the LRU chance for shared pages.

With that, the manager process could give a hint to several processes
and finally makes them paging out.

What do you think?