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

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Message-ID: <87inn448c9.fsf@concordia.ellerman.id.au>
Date:   Mon, 20 Mar 2017 20:15:50 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, 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-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above 47-bits

"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> writes:
> "Kirill A. Shutemov" <kirill@...temov.name> writes:
>> On Fri, Mar 17, 2017 at 11:23:54PM +0530, Aneesh Kumar K.V wrote:
>>> So if I have done a successful mmap which returned > 128TB what should a
>>> following mmap(0,...) return ? Should that now search the *full* address
>>> space or below 128TB ?
>>
>> No, I don't think so. And this implementation doesn't do this.
>>
>> It's safer this way: if an library can't handle high addresses, it's
>> better not to switch it automagically to full address space if other part
>> of the process requested high address.
>
> What is the epectation when the hint addr is below 128TB but addr + len >
> 128TB ? Should such mmap request fail ?

Yeah I think that makes sense, it retains the existing behaviour unless
the hint itself is >= 128TB.

cheers