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Date: Wed, 15 Mar 2017 18:42:05 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Andi Kleen <ak@linux.intel.com>, Dave Hansen <dave.hansen@intel.com>,
        Andy Lutomirski <luto@amacapital.net>, Michal Hocko <mhocko@suse.com>,
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        linux-mm <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/6] x86: 5-level paging enabling for v4.12, Part 1
Message-ID: <20170315154205.33hvpvkbjypgkd7g@node.shutemov.name>
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On Tue, Mar 14, 2017 at 10:48:51AM -0700, Linus Torvalds wrote:
> On Tue, Mar 14, 2017 at 12:47 AM, Ingo Molnar <mingo@kernel.org> wrote:
> >
> > I've also applied the GUP patch, with the assumption that you'll address Linus's
> > request to switch x86 over to the generic version.
> 
> Note that switching over to the generic version is somewhat fraught
> with subtle issues:
> 
>  (a) we need to make sure that x86 actually matches the required
> semantics for the generic GUP.
> 
>  (b) we need to make sure the atomicity of the page table reads is ok.
> 
>  (c) need to verify the maximum VM address properly

There's another difference with generic version: it uses
page_cache_get_speculative() instead of plain get_page() on x86.
That's somewhat more expensive, but probably fine.

-- 
 Kirill A. Shutemov