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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 13 Dec 2017 10:23:59 -0800
Message-ID: <CA+55aFxjxm3qTaH2cw4o8eOxUjh0AcPW5U6mDc1SS3uRUBFGGA@mail.gmail.com>
Subject: Re: [patch 05/16] mm: Allow special mappings with user access cleared
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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>

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

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