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

[Kirill A. Shutemov]

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@xxxxxxxxxx> 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