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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 15 Dec 2017 18:52:43 -0800
Message-ID: <CA+55aFzehO00PH-WQuHJroRddiRMyLhO66b4Cv2sJA=7D2CeAw@mail.gmail.com>
Subject: Re: [PATCH v2 01/17] mm/gup: Fixup p*_access_permitted()
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To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dave Hansen <dave.hansen@intel.com>, Dan Williams <dan.j.williams@intel.com>, Peter Zijlstra <peterz@infradead.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>, the arch/x86 maintainers <x86@kernel.org>, Andy Lutomirsky <luto@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 <linux-mm@kvack.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

On Fri, Dec 15, 2017 at 6:48 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> Treating protection key bits as "escalate to page fault and let that
> deal with the checks" should be fine

Well, it's *semantically* fine and I think it's the right model from
that standpoint.

However, since the main use case of protection keys is probably
databases (Dave?) and since those also might be performance-sensitive
about direct-IO doing page table lookups, it might not be great in
practice.

             Linus

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