linux-kernel - Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX

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Message-ID: <CALCETrW91F0=GLWt4yBJVbt7U=E6nLXDUMNUvTpnmn6XLjaY6g@mail.gmail.com>
Date:   Fri, 17 Feb 2017 15:02:33 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "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>,
        "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>,
        Catalin Marinas <catalin.marinas@....com>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR

On Fri, Feb 17, 2017 at 1:01 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Fri, Feb 17, 2017 at 12:12 PM, Andy Lutomirski <luto@...capital.net> wrote:
>>
>> At the very least, I'd want to see
>> MAP_FIXED_BUT_DONT_BLOODY_UNMAP_ANYTHING.  I *hate* the current
>> interface.
>
> That's unrelated, but I guess w could add a MAP_NOUNMAP flag, and then
> you can use MAP_FIXED | MAP_NOUNMAP or something.
>
> But that has nothing to do with the 47-vs-56 bit issue.
>
>> How about MAP_LIMIT where the address passed in is interpreted as an
>> upper bound instead of a fixed address?
>
> Again, that's a unrelated semantic issue. Right now - if you don't
> pass in MAP_FIXED at all, the "addr" argument is used as a starting
> value for deciding where to find an unmapped area. But there is no way
> to specify the end. That would basically be what the process control
> thing would be (not per-system-call, but per-thread ).
>

What I'm trying to say is: if we're going to do the route of 48-bit
limit unless a specific mmap call requests otherwise, can we at least
have an interface that doesn't suck?