From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Aneesh Kumar K.V" Subject: Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above 47-bits Date: Sun, 19 Mar 2017 13:54:03 +0530 Message-ID: <877f3lfzdo.fsf@skywalker.in.ibm.com> References: <20170313055020.69655-1-kirill.shutemov@linux.intel.com> <20170313055020.69655-27-kirill.shutemov@linux.intel.com> <87a88jg571.fsf@skywalker.in.ibm.com> <20170317175714.3bvpdylaaudf4ig2@node.shutemov.name> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <20170317175714.3bvpdylaaudf4ig2@node.shutemov.name> Sender: owner-linux-mm@kvack.org To: "Kirill A. Shutemov" Cc: "Kirill A. Shutemov" , Linus Torvalds , Andrew Morton , x86@kernel.org, Thomas Gleixner , Ingo Molnar , Arnd Bergmann , "H. Peter Anvin" , Andi Kleen , Dave Hansen , Andy Lutomirski , Michal Hocko , linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-Id: linux-arch.vger.kernel.org "Kirill A. Shutemov" writes: > On Fri, Mar 17, 2017 at 11:23:54PM +0530, Aneesh Kumar K.V wrote: >> "Kirill A. Shutemov" 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 ? -aneesh -- 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:47097 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751181AbdCSIZv (ORCPT ); Sun, 19 Mar 2017 04:25:51 -0400 Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v2J8DYdn028040 for ; Sun, 19 Mar 2017 04:25:06 -0400 Received: from e23smtp02.au.ibm.com (e23smtp02.au.ibm.com [202.81.31.144]) by mx0a-001b2d01.pphosted.com with ESMTP id 2990ymgmg0-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Sun, 19 Mar 2017 04:25:06 -0400 Received: from localhost by e23smtp02.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sun, 19 Mar 2017 18:25:03 +1000 From: "Aneesh Kumar K.V" Subject: Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above 47-bits In-Reply-To: <20170317175714.3bvpdylaaudf4ig2@node.shutemov.name> References: <20170313055020.69655-1-kirill.shutemov@linux.intel.com> <20170313055020.69655-27-kirill.shutemov@linux.intel.com> <87a88jg571.fsf@skywalker.in.ibm.com> <20170317175714.3bvpdylaaudf4ig2@node.shutemov.name> Date: Sun, 19 Mar 2017 13:54:03 +0530 MIME-Version: 1.0 Content-Type: text/plain Message-ID: <877f3lfzdo.fsf@skywalker.in.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: "Kirill A. Shutemov" Cc: "Kirill A. Shutemov" , Linus Torvalds , Andrew Morton , x86@kernel.org, Thomas Gleixner , Ingo Molnar , Arnd Bergmann , "H. Peter Anvin" , Andi Kleen , Dave Hansen , Andy Lutomirski , Michal Hocko , linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Message-ID: <20170319082403.08HWkK8ujP1SdLeFzJcqMqVXuNBRR6_ZwlFtX6PMeBI@z> "Kirill A. Shutemov" writes: > On Fri, Mar 17, 2017 at 11:23:54PM +0530, Aneesh Kumar K.V wrote: >> "Kirill A. Shutemov" 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 ? -aneesh