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[209.85.208.179]) by smtp.gmail.com with ESMTPSA id y3sm9499001lfh.97.2019.10.23.13.15.29 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Oct 2019 13:15:29 -0700 (PDT) Received: by mail-lj1-f179.google.com with SMTP id c4so7376019lja.11 for ; Wed, 23 Oct 2019 13:15:29 -0700 (PDT) X-Received: by 2002:a2e:2e10:: with SMTP id u16mr3404094lju.97.1571861729069; Wed, 23 Oct 2019 13:15:29 -0700 (PDT) MIME-Version: 1.0 References: <20191012191602.45649-1-dancol@google.com> <20191012191602.45649-4-dancol@google.com> <20191023190959.GA9902@redhat.com> In-Reply-To: <20191023190959.GA9902@redhat.com> From: Linus Torvalds Date: Wed, 23 Oct 2019 16:15:12 -0400 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 3/7] Add a UFFD_SECURE flag to the userfaultfd API. To: Andrea Arcangeli Cc: Andy Lutomirski , Jann Horn , Daniel Colascione , Pavel Emelyanov , Lokesh Gidra , Nick Kralevich , Nosh Minwalla , Tim Murray , Mike Rapoport , Linux API , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 23, 2019 at 3:10 PM Andrea Arcangeli wrote: > > That wouldn't break the ABI, no more than when if you boot a kernel > built with CONFIG_USERFAULTFD=n. What? No. You're entirely incorrect. If USEFAULTFD no longer works, and if people depend on it, then it's breaking the ABI. End of story. No weaselwording of "as if built with CONFIG_USERFAULTFD=n" allowed, no garbage. Btw, the whole "breaking the ABI" is misleading wording anyway. It's irrelevant. You can "break" the ABI all you want by changing semantics, adding or removing features, or making it do anything else - as long as nobody notices. Because the only thing that matters is that it doesn't break any user workflows. That's _all_ that matters, but it's a big deal, and it means that your fantasy reading of what "ABI" means is irrelevant. Just because there's a config option to turn something off, doesn't mean that you can then claim that you can do whatever. So your statement is nonsensical and pointless. Please don't spread this kind of bogus claims. Linus