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Date:   Wed, 29 Nov 2017 16:50:09 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc:     linux-api@vger.kernel.org, Khalid Aziz <khalid.aziz@oracle.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Andrew Morton <akpm@linux-foundation.org>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
        Andrea Arcangeli <aarcange@redhat.com>, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>, linux-arch@vger.kernel.org,
        Florian Weimer <fweimer@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Abdul Haleem <abdhalee@linux.vnet.ibm.com>,
        Joel Stanley <joel@jms.id.au>,
        Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE
Message-ID: <20171129155009.i5xai77rrapsyrd2@dhcp22.suse.cz>
References: <20171129144219.22867-1-mhocko@kernel.org>
 <b154b794-7a8b-995e-0954-9234b9446b31@prevas.dk>
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On Wed 29-11-17 16:13:53, Rasmus Villemoes wrote:
> On 2017-11-29 15:42, Michal Hocko wrote:
[...]
> >The flag is introduced as a completely
> > new one rather than a MAP_FIXED extension because of the backward
> > compatibility. We really want a never-clobber semantic even on older
> > kernels which do not recognize the flag. Unfortunately mmap sucks wrt.
> > flags evaluation because we do not EINVAL on unknown flags. On those
> > kernels we would simply use the traditional hint based semantic so the
> > caller can still get a different address (which sucks) but at least not
> > silently corrupt an existing mapping. I do not see a good way around
> > that.
> 
> I think it would be nice if this rationale was in the 1/2 changelog,
> along with the hint about what userspace that wants to be compatible
> with old kernels will have to do (namely, check that it got what it
> requested) - which I see you did put in the man page.

OK, I've added there.

-- 
Michal Hocko
SUSE Labs

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