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Date:   Mon, 24 Apr 2023 14:53:00 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Jan Kara <jack@suse.cz>
Cc:     Lorenzo Stoakes <lstoakes@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Jens Axboe <axboe@kernel.dk>,
        Matthew Wilcox <willy@infradead.org>,
        Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>,
        Leon Romanovsky <leon@kernel.org>,
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        Nelson Escobar <neescoba@cisco.com>,
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        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Ian Rogers <irogers@google.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Bjorn Topel <bjorn@kernel.org>,
        Magnus Karlsson <magnus.karlsson@intel.com>,
        Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
        Jonathan Lemon <jonathan.lemon@gmail.com>,
        "David S . Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
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        Richard Cochran <richardcochran@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        linux-fsdevel@vger.kernel.org, linux-perf-users@vger.kernel.org,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH] mm/gup: disallow GUP writing to file-backed mappings by
 default
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On Mon, Apr 24, 2023 at 06:09:52PM +0200, Jan Kara wrote:

> So I'm maybe missing a bigger picture why we would like a change like this.
> Because we still need to teach filesystems to handle pinned pages for the
> usecases you don't forbid and for which we know there are users and then
> what's the benefit of this patch?

It immediately closes a security hole we have been talking about
fixing for years already and still don't have a full fix for.

An acknowledgment that this is not going to go away and starting to
clamp down on the insecurity may motivate some investment in the
proper fix. :)

Jason