Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1753547AbdLMSYC (ORCPT <rfc822;w@1wt.eu>);
        Wed, 13 Dec 2017 13:24:02 -0500
Received: from mail-ot0-f195.google.com ([74.125.82.195]:45874 "EHLO
        mail-ot0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1752434AbdLMSYA (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 13 Dec 2017 13:24:00 -0500
X-Google-Smtp-Source: ACJfBotiKh/Ad5w3f/HsP1kbS3UwJRmLhMUttiGXJzNxYtaAp85gaRdn3/CqHoUfVJrQXRghY/WGefaLuZ69DXgm2h4=
MIME-Version: 1.0
In-Reply-To: <b40719da-a23b-72a4-ddde-54c2f5d96820@intel.com>
References: <20171212173221.496222173@linutronix.de> <20171212173333.669577588@linutronix.de>
 <CALCETrXLeGGw+g7GiGDmReXgOxjB-cjmehdryOsFK4JB5BJAFQ@mail.gmail.com>
 <20171213122211.bxcb7xjdwla2bqol@hirez.programming.kicks-ass.net>
 <20171213125739.fllckbl3o4nonmpx@node.shutemov.name> <b303fac7-34af-5065-f996-4494fb8c09a2@intel.com>
 <20171213153202.qtxnloxoc66lhsbf@hirez.programming.kicks-ass.net>
 <e6ef40c8-8966-c973-3ae4-ac9475699e40@intel.com> <20171213155427.p24i2xdh2s65e4d2@hirez.programming.kicks-ass.net>
 <CA+55aFw0JTRDXked3_OJ+cFx59BE18yDWOt7-ZRTzFS10zYnrg@mail.gmail.com> <b40719da-a23b-72a4-ddde-54c2f5d96820@intel.com>
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 13 Dec 2017 10:23:59 -0800
X-Google-Sender-Auth: A_3Sr9Vbf_a1_DnQ4uqV6okOBjQ
Message-ID: <CA+55aFxjxm3qTaH2cw4o8eOxUjh0AcPW5U6mDc1SS3uRUBFGGA@mail.gmail.com>
Subject: Re: [patch 05/16] mm: Allow special mappings with user access cleared
To: Dave Hansen <dave.hansen@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Borislav Petkov <bpetkov@suse.de>,
        Greg KH <gregkh@linuxfoundation.org>, Kees Cook <keescook@google.com>,
        Hugh Dickins <hughd@google.com>, Brian Gerst <brgerst@gmail.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        David Laight <David.Laight@aculab.com>,
        Eduardo Valentin <eduval@amazon.com>,
        "Liguori, Anthony" <aliguori@amazon.com>,
        Will Deacon <will.deacon@arm.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        "Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 933
Lines: 22

On Wed, Dec 13, 2017 at 10:21 AM, Dave Hansen <dave.hansen@intel.com> wrote:
> On 12/13/2017 10:08 AM, Linus Torvalds wrote:
>> On Wed, Dec 13, 2017 at 7:54 AM, Peter Zijlstr <peterz@infradead.org> wrote:
>>> Which is why get_user_pages() _should_ enforce this.
>>>
>>> What use are protection keys if you can trivially circumvent them?
>> No, we will *not* worry about protection keys in get_user_pages().
>
> We did introduce some support for it here:
>
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=33a709b25a760b91184bb335cf7d7c32b8123013

Ugh. I never realized.

We should revert that, I feel. It's literally extra complexity for no
actual real gain, and there is a real downside: the extra complexity
that will cause people to get things wrong.

This thread about us getting it wrong is just the proof. I vote for
not trying to "fix" this case, let's just remove it.

                  Linus