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From:   Florian Weimer <fweimer@redhat.com>
To:     Brian Geffon <bgeffon@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        "Michael S . Tsirkin" <mst@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>, linux-api@vger.kernel.org,
        Andy Lutomirski <luto@amacapital.net>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Sonny Rao <sonnyrao@google.com>,
        Minchan Kim <minchan@kernel.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Yu Zhao <yuzhao@google.com>, Jesse Barnes <jsbarnes@google.com>
Subject: Re: [PATCH v2] mm: Add MREMAP_DONTUNMAP to mremap().
References: <20200123014627.71720-1-bgeffon@google.com>
        <20200124190625.257659-1-bgeffon@google.com>
        <87imkxxl5d.fsf@oldenburg2.str.redhat.com>
        <CADyq12xCpTzLpYC16FjnM60tHhCfnccNfg6JJuqcBd_6ACDGcQ@mail.gmail.com>
Date:   Thu, 30 Jan 2020 13:19:39 +0100
In-Reply-To: <CADyq12xCpTzLpYC16FjnM60tHhCfnccNfg6JJuqcBd_6ACDGcQ@mail.gmail.com>
        (Brian Geffon's message of "Mon, 27 Jan 2020 14:33:44 -0800")
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* Brian Geffon:

> Hi Florian,
> copy_vma will make a copy of the existing VMA leaving the old VMA
> unchanged, so the source keeps its existing protections, this is what
> makes it very useful along with userfaultfd.

I see.  On the other hand, it's impossible to get the PROT_NONE behavior
by a subsequent mprotect call because the mremap has to fail in some
cases in vm.overcommit_memory=2 mode.  But maybe that other behavior can
be provided with a different flag if it turns out to be useful in the
future.

Thanks,
Florian