From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f198.google.com (mail-qk0-f198.google.com [209.85.220.198]) by kanga.kvack.org (Postfix) with ESMTP id E9F1B6B0005 for ; Wed, 22 Jun 2016 15:20:33 -0400 (EDT) Received: by mail-qk0-f198.google.com with SMTP id y77so154030460qkb.2 for ; Wed, 22 Jun 2016 12:20:33 -0700 (PDT) Received: from mail-vk0-x234.google.com (mail-vk0-x234.google.com. [2607:f8b0:400c:c05::234]) by mx.google.com with ESMTPS id 92si899186uab.168.2016.06.22.12.20.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 22 Jun 2016 12:20:33 -0700 (PDT) Received: by mail-vk0-x234.google.com with SMTP id u64so75431003vkf.3 for ; Wed, 22 Jun 2016 12:20:33 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20160622191843.GA2045@uranus.lan> References: <4A8E6E6D-6CF7-4964-A62E-467AE287D415@linaro.org> <576AA67E.50009@codeaurora.org> <20160622191843.GA2045@uranus.lan> From: Andy Lutomirski Date: Wed, 22 Jun 2016 12:20:13 -0700 Message-ID: Subject: Re: JITs and 52-bit VA Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Cyrill Gorcunov Cc: Christopher Covington , Maxim Kuvyrkov , Linaro Dev Mailman List , Arnd Bergmann , Mark Brown , "linux-mm@kvack.org" , Dmitry Safonov On Wed, Jun 22, 2016 at 12:18 PM, Cyrill Gorcunov wrote: > On Wed, Jun 22, 2016 at 08:13:29AM -0700, Andy Lutomirski wrote: > ... >> > >> > However based on the above discussion, it appears that some sort of >> > prctl(PR_GET_TASK_SIZE, ...) and prctl(PR_SET_TASK_SIZE, ...) may be >> > preferable for AArch64. (And perhaps other justifications for the new >> > calls influences the x86 decisions.) What do folks think? >> >> I would advocate a slightly different approach: >> >> - Keep TASK_SIZE either unconditionally matching the hardware or keep >> TASK_SIZE as the actual logical split between user and kernel >> addresses. Don't let it change at runtime under any circumstances. >> The reason is that there have been plenty of bugs and >> overcomplications that result from letting it vary. For example, if >> (addr < TASK_SIZE) really ought to be the correct check (assuming >> USER_DS, anyway) for whether dereferencing addr will access user >> memory, at least on architectures with a global address space (which >> is most of them, I think). >> >> - If needed, introduce a clean concept of the maximum address that >> mmap will return, but don't call it TASK_SIZE. So, if a user program >> wants to limit itself to less than the full hardware VA space (or less >> than 63 bits, for that matter), it can. >> >> As an example, a 32-bit x86 program really could have something mapped >> above the 32-bit boundary. It just wouldn't be useful, but the kernel >> should still understand that it's *user* memory. >> >> So you'd have PR_SET_MMAP_LIMIT and PR_GET_MMAP_LIMIT or similar instead. > > +1. Also it might be (not sure though, just guessing) suitable to do such > thing via memory cgroup controller, instead of carrying this limit per > each process (or task structure/vma or mm). I think we'll want this per mm. After all, a high-VA-limit-aware bash should be able run high-VA-unaware programs without fiddling with cgroups. -- 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