From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f199.google.com (mail-qt0-f199.google.com [209.85.216.199]) by kanga.kvack.org (Postfix) with ESMTP id 0B7806B025E for ; Wed, 28 Dec 2016 21:54:02 -0500 (EST) Received: by mail-qt0-f199.google.com with SMTP id d22so127482623qtd.3 for ; Wed, 28 Dec 2016 18:54:02 -0800 (PST) Received: from mail-qt0-f182.google.com (mail-qt0-f182.google.com. [209.85.216.182]) by mx.google.com with ESMTPS id 4si2231118qkk.68.2016.12.28.18.54.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 28 Dec 2016 18:54:01 -0800 (PST) Received: by mail-qt0-f182.google.com with SMTP id c47so363806777qtc.2 for ; Wed, 28 Dec 2016 18:54:01 -0800 (PST) Subject: Re: [RFC, PATCHv2 29/29] mm, x86: introduce RLIMIT_VADDR References: <20161227015413.187403-1-kirill.shutemov@linux.intel.com> <20161227015413.187403-30-kirill.shutemov@linux.intel.com> <20161227022405.GA8780@node.shutemov.name> From: Carlos O'Donell Message-ID: <3a168403-26f7-ac8d-3086-848178be6005@redhat.com> Date: Wed, 28 Dec 2016 21:53:58 -0500 MIME-Version: 1.0 In-Reply-To: <20161227022405.GA8780@node.shutemov.name> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" , Andy Lutomirski Cc: "Kirill A. Shutemov" , Linus Torvalds , Andrew Morton , X86 ML , Thomas Gleixner , Ingo Molnar , Arnd Bergmann , "H. Peter Anvin" , Andi Kleen , Dave Hansen , linux-arch , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Linux API On 12/26/2016 09:24 PM, Kirill A. Shutemov wrote: > On Mon, Dec 26, 2016 at 06:06:01PM -0800, Andy Lutomirski wrote: >> On Mon, Dec 26, 2016 at 5:54 PM, Kirill A. Shutemov >> wrote: >>> This patch introduces new rlimit resource to manage maximum virtual >>> address available to userspace to map. >>> >>> 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 high bit in pointers to encode their >>> information. It collides with valid pointers with 5-level paging and >>> leads to crashes. >>> >>> The patch aims to address this compatibility issue. >>> >>> MM would use min(RLIMIT_VADDR, TASK_SIZE) as upper limit of virtual >>> address available to map by userspace. >>> >>> The default hard limit will be RLIM_INFINITY, which basically means that >>> TASK_SIZE limits available address space. >>> >>> The soft limit will also be RLIM_INFINITY everywhere, but the machine >>> with 5-level paging enabled. In this case, soft limit would be >>> (1UL << 47) - PAGE_SIZE. Ita??s current x86-64 TASK_SIZE_MAX with 4-level >>> paging which known to be safe >>> >>> New rlimit resource would follow usual semantics with regards to >>> inheritance: preserved on fork(2) and exec(2). This has potential to >>> break application if limits set too wide or too narrow, but this is not >>> uncommon for other resources (consider RLIMIT_DATA or RLIMIT_AS). >>> >>> As with other resources you can set the limit lower than current usage. >>> It would affect only future virtual address space allocations. >>> >>> Use-cases for new rlimit: >>> >>> - Bumping the soft limit to RLIM_INFINITY, allows current process all >>> its children to use addresses above 47-bits. >>> >>> - Bumping the soft limit to RLIM_INFINITY after fork(2), but before >>> exec(2) allows the child to use addresses above 47-bits. >>> >>> - Lowering the hard limit to 47-bits would prevent current process all >>> its children to use addresses above 47-bits, unless a process has >>> CAP_SYS_RESOURCES. >>> >>> - Ita??s also can be handy to lower hard or soft limit to arbitrary >>> address. User-mode emulation in QEMU may lower the limit to 32-bit >>> to emulate 32-bit machine on 64-bit host. >> >> I tend to think that this should be a personality or an ELF flag, not >> an rlimit. > > My plan was to implement ELF flag on top. Basically, ELF flag would mean > that we bump soft limit to hard limit on exec. Could you clarify what you mean by an "ELF flag?" -- Cheers, Carlos. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org