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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>, linux-kernel@vger.kernel.org,
        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>
Date:   Mon, 27 Jan 2020 11:13:02 +0100
In-Reply-To: <20200124190625.257659-1-bgeffon@google.com> (Brian Geffon's
        message of "Fri, 24 Jan 2020 11:06:25 -0800")
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* Brian Geffon:

> When remapping an anonymous, private mapping, if MREMAP_DONTUNMAP is
> set, the source mapping will not be removed. Instead it will be
> cleared as if a brand new anonymous, private mapping had been created
> atomically as part of the mremap() call.  If a userfaultfd was watching
> the source, it will continue to watch the new mapping.  For a mapping
> that is shared or not anonymous, MREMAP_DONTUNMAP will cause the
> mremap() call to fail. MREMAP_DONTUNMAP implies that MREMAP_FIXED is
> also used. The final result is two equally sized VMAs where the
> destination contains the PTEs of the source.

What will be the protection flags of the source mapping?  Will they
remain unchanged?  Or PROT_NONE?

Thanks,
Florian