linux-kernel - Re: [patch 05/16] mm: Allow special mappings with user access cleared

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Date:   Wed, 13 Dec 2017 16:04:53 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bpetkov@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>, aliguori@...zon.com,
        Will Deacon <will.deacon@....com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        kirill.shutemov@...ux.intel.com, aneesh.kumar@...ux.vnet.ibm.com
Subject: Re: [patch 05/16] mm: Allow special mappings with user access cleared

On Wed, Dec 13, 2017 at 04:00:07PM +0100, Peter Zijlstra wrote:
> On Wed, Dec 13, 2017 at 05:43:39PM +0300, Kirill A. Shutemov wrote:
> > > am I perchance looking at the wrong tee?
> > 
> > I'm looking at Linus' tree.
> 
> Clearly I'm not synced up enough... :/
> 
> > It was changed recently:
> > 	5c9d2d5c269c ("mm: replace pte_write with pte_access_permitted in fault + gup paths")
> > 
> 
> Indeed. So FOLL_GET should also get these tests and, as you said, the
> other levels too.
> 
> I would like FOLL_POPULATE (doesn't have FOLL_GET) to be allowed
> 'access'.

Similarly, should we avoid arch_vma_access_permitted() if !FOLL_GET ?