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

From	Dave Hansen <dave.hansen@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR
Date	2017-02-17 18:30 +0100
Message-ID	<tbUw1-7dc-13@gated-at.bofh.it> (permalink)
References	<tbRy9-5mq-3@gated-at.bofh.it> <tbRyb-5mq-61@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 02/17/2017 06:13 AM, Kirill A. Shutemov wrote:
> +/*
> + * Default maximum virtual address. This is required for
> + * compatibility with applications that assumes 47-bit VA.
> + * The limit can be changed with prctl(PR_SET_MAX_VADDR).
> + */
> +#define MAX_VADDR_DEFAULT	((1UL << 47) - PAGE_SIZE)

This is a bit goofy.  It's not the largest virtual adddress that can be
accessed, but the beginning of the last page.

Isn't this easier to deal with in userspace if we make it a "limit", so
we can do:

	if (addr >= limit)
		// error

Now, we have to do:

	prctl(PR_GET_MAX_VADDR, &max_vaddr, 0, 0, 0);
	if (addr > (max_vaddr + PAGE_SIZE))
		// error

I don't care what you track in the kernel, but I think we need to
provide a more usable number out to userspace.

Thread

[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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