linux-kernel - Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above 47-bits

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Message-ID: <20170320183854.GB22036@bombadil.infradead.org>
Date:   Mon, 20 Mar 2017 11:38:54 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     hpa@...or.com
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Michal Hocko <mhocko@...e.com>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Hansen <dave.hansen@...el.com>, linux-mm@...ck.org,
        x86@...nel.org, Andi Kleen <ak@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above
 47-bits

On Mon, Mar 20, 2017 at 11:08:41AM -0700, hpa@...or.com wrote:
> On March 19, 2017 1:26:58 AM PDT, "Kirill A. Shutemov" <kirill@...temov.name> wrote:
> >On Mar 19, 2017 09:25, "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:
> > > What is the epectation when the hint addr is below 128TB but addr + len
> > > 128TB ? Should such mmap request fail ?
> >
> >Yes, I believe so.
> 
> This *better* be conditional on some kind of settable limit.  Having a
> barrier in the middle of the address space for no apparent reason to
> "clean" software is insane.

I disagree with Kirill here.  If addr+len > 128TB, I think we should
assume the application is 57-bit aware.

Specifying hint addresses is such a rare thing to do anyway.