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Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR

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On Fri, Feb 17, 2017 at 12:02 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Fri, Feb 17, 2017 at 6:13 AM, Kirill A. Shutemov
> <kirill.shutemov@linux.intel.com> wrote:
>> This patch introduces two new prctl(2) handles to manage maximum virtual
>> address available to userspace to map.
>
> So this is my least favorite patch of the whole series, for a couple of reasons:
>
>  (a) adding new code, and mixing it with the mindless TASK_SIZE ->
> get_max_addr() conversion.
>
>  (b) what's the point of that whole TASK_SIZE vs get_max_addr() thing?
> When use one, when the other?
>
> so I think this patch needs a lot more thought and/or explanation.
>
> Honestly, (a) is a no-brainer, and can be fixed by just splitting the
> patch up. But I think (b) is more fundamental.
>
> In particular, I think that get_max_addr() thing is badly defined.
> When should you use TASK_SIZE, when should you use TASK_SIZE_MAX, and
> when should you use get_max_addr()? I don't find that clear at all,
> and I think that needs to be a whole lot more explicit and documented.
>
> I also get he feeling that the whole thing is unnecessary. I'm
> wondering if we should just instead say that the whole 47 vs 56-bit
> virtual address is _purely_ about "get_unmapped_area()", and nothing
> else.
>
> IOW, I'm wondering if we can't just say that
>
>  - if the processor and kernel support 56-bit user address space, then
> you can *always* use the whole space
>
>  - but by default, get_unmapped_area() will only return mappings that
> fit in the 47 bit address space.
>
> So if you use MAP_FIXED and give an address in the high range, it will
> just always work, and the MM will always consider the task size to be
> the full address space.

At the very least, I'd want to see
MAP_FIXED_BUT_DONT_BLOODY_UNMAP_ANYTHING.  I *hate* the current
interface.

>
> But for the common case where a process does no use MAP_FIXED, the
> kernel will never give a high address by default, and you have to do
> the process control thing to say "I want those high addresses".
>
> Hmm?

How about MAP_LIMIT where the address passed in is interpreted as an
upper bound instead of a fixed address?

--Andy

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[PATCHv3 00/33] 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:20 +0100
  [PATCHv3 30/33] x86/mm: make kernel_physical_mapping_init() support 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:20 +0100
  [PATCHv3 14/33] x86/kexec: support p4d_t "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:20 +0100
  [PATCHv3 25/33] x86/dump_pagetables: support 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:20 +0100
  [PATCHv3 12/33] x86/mm: add support of p4d_t in vmalloc_fault() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:20 +0100
  [PATCHv3 10/33] x86/gup: add 5-level paging support "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:20 +0100
  [PATCHv3 27/33] x86/espfix: support 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:20 +0100
  [PATCHv3 05/33] asm-generic: introduce <asm-generic/pgtable-nop4d.h> "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:20 +0100
  [PATCHv3 15/33] x86/efi: handle p4d in EFI pagetables "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:20 +0100
    Re: [PATCHv3 15/33] x86/efi: handle p4d in EFI pagetables Matt Fleming <matt@codeblueprint.co.uk> - 2017-02-28 13:40 +0100
  [PATCHv3 32/33] x86: enable 5-level paging support "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:20 +0100
  [PATCHv3 26/33] x86/kasan: extend to support 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:20 +0100
  [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:20 +0100
    Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR Andy Lutomirski <luto@amacapital.net> - 2017-02-17 18:00 +0100
      Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR Dmitry Safonov <0x7f454c46@gmail.com> - 2017-02-21 13:00 +0100
        Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and  PR_GET_MAX_VADDR "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-02-21 13:50 +0100
    Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and  PR_GET_MAX_VADDR Dave Hansen <dave.hansen@intel.com> - 2017-02-17 18:30 +0100
      Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR Andy Lutomirski <luto@amacapital.net> - 2017-02-17 18:30 +0100
    Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR Linus Torvalds <torvalds@linux-foundation.org> - 2017-02-17 21:10 +0100
      Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR Andy Lutomirski <luto@amacapital.net> - 2017-02-17 21:30 +0100
        Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR Linus Torvalds <torvalds@linux-foundation.org> - 2017-02-17 22:10 +0100
          Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR Andy Lutomirski <luto@amacapital.net> - 2017-02-18 00:10 +0100
            Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR hpa@zytor.com - 2017-02-18 00:20 +0100
            Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR Michael Pratt <mpratt@google.com> - 2017-02-21 07:20 +0100
            Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and  PR_GET_MAX_VADDR Catalin Marinas <catalin.marinas@arm.com> - 2017-02-21 11:40 +0100
              Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and  PR_GET_MAX_VADDR "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-02-21 11:50 +0100
                Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and  PR_GET_MAX_VADDR Catalin Marinas <catalin.marinas@arm.com> - 2017-02-21 12:00 +0100
      Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and  PR_GET_MAX_VADDR Dave Hansen <dave.hansen@intel.com> - 2017-02-17 22:10 +0100
        Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR Linus Torvalds <torvalds@linux-foundation.org> - 2017-02-17 22:20 +0100
          Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR hpa@zytor.com - 2017-02-17 23:00 +0100
      Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and  PR_GET_MAX_VADDR "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-02-18 10:30 +0100
        Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and  PR_GET_MAX_VADDR "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-02-20 14:20 +0100
          Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and  PR_GET_MAX_VADDR Dave Hansen <dave.hansen@intel.com> - 2017-02-21 21:50 +0100
            Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and  PR_GET_MAX_VADDR "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-02-22 14:10 +0100
  [PATCHv3 23/33] x86/paravirt: make paravirt code support 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100
  [PATCHv3 13/33] x86/power: support p4d_t in hibernate code "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100
  [PATCHv3 28/33] x86/mm: add support of additional page table level during early boot "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100
  [PATCHv3 21/33] x86/asm: remove __VIRTUAL_MASK_SHIFT==47 assert "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100
  [PATCHv3 04/33] arch, mm: convert all architectures to use 5level-fixup.h "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100
  [PATCHv3 01/33] x86/cpufeature: Add 5-level paging detection "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100
  [PATCHv3 08/33] x86: basic changes into headers for 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100
  [PATCHv3 03/33] asm-generic: introduce __ARCH_USE_5LEVEL_HACK "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100
  [PATCHv3 07/33] mm: introduce __p4d_alloc() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100
  [PATCHv3 16/33] x86/mm/pat: handle additional page table "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100
  [PATCHv3 19/33] x86: convert the rest of the code to support p4d_t "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100
  [PATCHv3 11/33] x86/ident_map: add 5-level paging support "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100
  [PATCHv3 18/33] x86/xen: convert __xen_pgd_walk() and xen_cleanmfnmap() to support p4d "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-02-17 15:30 +0100

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