From: hpa@zytor.com
To: "Kirill A. Shutemov" <kirill@shutemov.name>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: linux-arch <linux-arch@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Michal Hocko <mhocko@suse.com>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Arnd Bergmann <arnd@arndb.de>,
Andy Lutomirski <luto@amacapital.net>,
Dave Hansen <dave.hansen@intel.com>,
linux-mm@kvack.org, x86@kernel.org,
Andi Kleen <ak@linux.intel.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above 47-bits
Date: Mon, 20 Mar 2017 11:08:41 -0700 [thread overview]
Message-ID: <95631D05-2CA2-4967-A29E-DB396C76F62D@zytor.com> (raw)
In-Reply-To: <CAFZ8GQx2JmEECQHEsKOymP8nDv9YHfLgcK80R75gM+r-1q-owQ@mail.gmail.com>
On March 19, 2017 1:26:58 AM PDT, "Kirill A. Shutemov" <kirill@shutemov.name> wrote:
>On Mar 19, 2017 09:25, "Aneesh Kumar K.V"
><aneesh.kumar@linux.vnet.ibm.com>
>wrote:
>
>"Kirill A. Shutemov" <kirill@shutemov.name> writes:
>
>> On Fri, Mar 17, 2017 at 11:23:54PM +0530, Aneesh Kumar K.V wrote:
>>> "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> writes:
>>>
>>> > On x86, 5-level paging enables 56-bit userspace virtual address
>space.
>>> > Not all user space is ready to handle wide addresses. It's known
>that
>>> > at least some JIT compilers use higher bits in pointers to encode
>their
>>> > information. It collides with valid pointers with 5-level paging
>and
>>> > leads to crashes.
>>> >
>>> > To mitigate this, we are not going to allocate virtual address
>space
>>> > above 47-bit by default.
>>> >
>>> > But userspace can ask for allocation from full address space by
>>> > specifying hint address (with or without MAP_FIXED) above 47-bits.
>>> >
>>> > If hint address set above 47-bit, but MAP_FIXED is not specified,
>we
>try
>>> > to look for unmapped area by specified address. If it's already
>>> > occupied, we look for unmapped area in *full* address space,
>rather
>than
>>> > from 47-bit window.
>>> >
>>> > This approach helps to easily make application's memory allocator
>aware
>>> > about large address space without manually tracking allocated
>virtual
>>> > address space.
>>> >
>>>
>>> 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 ?
>
>
>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.
--
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next prev parent reply other threads:[~2017-03-20 18:08 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-13 5:49 [PATCH 00/26] x86: 5-level paging enabling for v4.12 Kirill A. Shutemov
2017-03-13 5:49 ` [PATCH 01/26] x86: basic changes into headers for 5-level paging Kirill A. Shutemov
2017-03-13 5:49 ` [PATCH 02/26] x86: trivial portion of 5-level paging conversion Kirill A. Shutemov
2017-03-13 5:49 ` [PATCH 03/26] x86/gup: add 5-level paging support Kirill A. Shutemov
2017-03-13 5:49 ` [PATCH 04/26] x86/ident_map: " Kirill A. Shutemov
2017-03-13 5:49 ` [PATCH 05/26] x86/mm: add support of p4d_t in vmalloc_fault() Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 06/26] x86/power: support p4d_t in hibernate code Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 07/26] x86/kexec: support p4d_t Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 08/26] x86/efi: handle p4d in EFI pagetables Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 09/26] x86/mm/pat: handle additional page table Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 10/26] x86/kasan: prepare clear_pgds() to switch to <asm-generic/pgtable-nop4d.h> Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 11/26] x86/xen: convert __xen_pgd_walk() and xen_cleanmfnmap() to support p4d Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 12/26] x86: convert the rest of the code to support p4d_t Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 13/26] x86: detect 5-level paging support Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 14/26] x86/asm: remove __VIRTUAL_MASK_SHIFT==47 assert Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 15/26] x86/mm: define virtual memory map for 5-level paging Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 16/26] x86/paravirt: make paravirt code support " Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 17/26] x86/mm: basic defines/helpers for CONFIG_X86_5LEVEL Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 18/26] x86/dump_pagetables: support 5-level paging Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 19/26] x86/kasan: extend to " Kirill A. Shutemov
2017-03-13 7:25 ` Dmitry Vyukov
2017-03-13 5:50 ` [PATCH 20/26] x86/espfix: " Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 21/26] x86/mm: add support of additional page table level during early boot Kirill A. Shutemov
2017-03-13 7:18 ` Ingo Molnar
2017-04-05 11:36 ` Kirill A. Shutemov
2017-04-05 15:32 ` Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 22/26] x86/mm: add sync_global_pgds() for configuration with 5-level paging Kirill A. Shutemov
2017-03-13 7:22 ` Ingo Molnar
2017-03-13 5:50 ` [PATCH 23/26] x86/mm: make kernel_physical_mapping_init() support " Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 24/26] x86/mm: add support for 5-level paging for KASLR Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 25/26] x86: enable 5-level paging support Kirill A. Shutemov
2017-03-13 5:50 ` [PATCH 26/26] x86/mm: allow to have userspace mappings above 47-bits Kirill A. Shutemov
2017-03-17 17:53 ` Aneesh Kumar K.V
2017-03-17 17:57 ` Kirill A. Shutemov
2017-03-19 8:24 ` Aneesh Kumar K.V
2017-03-19 8:26 ` Kirill A. Shutemov
2017-03-20 18:08 ` hpa [this message]
2017-03-20 18:38 ` Matthew Wilcox
2017-03-24 8:59 ` Kirill A. Shutemov
2017-03-19 8:55 ` Aneesh Kumar K.V
2017-03-24 9:03 ` Kirill A. Shutemov
2017-03-20 9:15 ` Michael Ellerman
2017-03-20 5:10 ` Aneesh Kumar K.V
2017-03-24 9:04 ` Kirill A. Shutemov
2017-03-24 9:14 ` Aneesh Kumar K.V
2017-03-24 9:30 ` Kirill A. Shutemov
2017-03-13 7:49 ` [PATCH 00/26] x86: 5-level paging enabling for v4.12 Ingo Molnar
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