linux-kernel - Re: [PATCH 0/6] x86: 5-level paging enabling for v4.12, Part 1

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Message-ID: <20170315154205.33hvpvkbjypgkd7g@node.shutemov.name>
Date:   Wed, 15 Mar 2017 18:42:05 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        Michal Hocko <mhocko@...e.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/6] x86: 5-level paging enabling for v4.12, Part 1

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@...nel.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