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Date:   Mon, 24 Apr 2023 02:43:56 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Lorenzo Stoakes <lstoakes@gmail.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
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Subject: Re: [PATCH v2] mm/gup: disallow GUP writing to file-backed mappings
 by default
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References: <c8ee7e02d3d4f50bb3e40855c53bda39eec85b7d.1682321768.git.lstoakes@gmail.com>
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I'm pretty sure DIRECT I/O reads that write into file backed mappings
are out there in the wild.

So while I wish we had never allowed this, the exercise seems futile and
instead we need to work on supporting this usecase, with the FOLL_PIN
infrastructure being a big step toward that.