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: Fri, 17 Mar 2017 23:23:54 +0530 Message-ID: <87a88jg571.fsf@skywalker.in.ibm.com> References: <20170313055020.69655-1-kirill.shutemov@linux.intel.com> <20170313055020.69655-27-kirill.shutemov@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <20170313055020.69655-27-kirill.shutemov@linux.intel.com> Sender: owner-linux-mm@kvack.org To: Linus Torvalds , Andrew Morton , x86@kernel.org, Thomas Gleixner , Ingo Molnar , Arnd Bergmann , "H. Peter Anvin" Cc: Andi Kleen , Dave Hansen , Andy Lutomirski , Michal Hocko , linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" List-Id: linux-arch.vger.kernel.org "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 ? -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 mx0b-001b2d01.pphosted.com ([148.163.158.5]:54247 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751100AbdCQTdL (ORCPT ); Fri, 17 Mar 2017 15:33:11 -0400 Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v2HHrpfC119519 for ; Fri, 17 Mar 2017 13:55:01 -0400 Received: from e23smtp04.au.ibm.com (e23smtp04.au.ibm.com [202.81.31.146]) by mx0a-001b2d01.pphosted.com with ESMTP id 298jc9p68t-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 17 Mar 2017 13:55:00 -0400 Received: from localhost by e23smtp04.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 18 Mar 2017 03:54:57 +1000 From: "Aneesh Kumar K.V" Subject: Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above 47-bits In-Reply-To: <20170313055020.69655-27-kirill.shutemov@linux.intel.com> References: <20170313055020.69655-1-kirill.shutemov@linux.intel.com> <20170313055020.69655-27-kirill.shutemov@linux.intel.com> Date: Fri, 17 Mar 2017 23:23:54 +0530 MIME-Version: 1.0 Content-Type: text/plain Message-ID: <87a88jg571.fsf@skywalker.in.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: "Kirill A. Shutemov" , Linus Torvalds , Andrew Morton , x86@kernel.org, Thomas Gleixner , Ingo Molnar , Arnd Bergmann , "H. Peter Anvin" Cc: Andi Kleen , Dave Hansen , Andy Lutomirski , Michal Hocko , linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Message-ID: <20170317175354.RWKVKkte4DNpUvsttEhL8LB5MR6XOVSjiq5KMfcjwn0@z> "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 ? -aneesh