From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751544AbdCSNBH (ORCPT ); Sun, 19 Mar 2017 09:01:07 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:37439 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751292AbdCSNBF (ORCPT ); Sun, 19 Mar 2017 09:01:05 -0400 From: "Aneesh Kumar K.V" 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 Subject: Re: [PATCH 26/26] x86/mm: allow to have userspace mappings above 47-bits In-Reply-To: <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> <877f3lfzdo.fsf@skywalker.in.ibm.com> Date: Sun, 19 Mar 2017 14:25:08 +0530 MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-MML: disable x-cbid: 17031908-0048-0000-0000-0000021507EA X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17031908-0049-0000-0000-000047BFBB76 Message-Id: <878to1sl1v.fsf@skywalker.in.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-03-19_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=5 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1702020001 definitions=main-1703190082 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "Aneesh Kumar K.V" writes: > "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 ? Considering that we have stack at the top (around 128TB) we may not be able to get a free area for such a request. But I guess the idea here is that if hint address is below 128TB, we behave as though our TASK_SIZE is 128TB ? Is that correct ? -aneesh 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 14:25:08 +0530 Message-ID: <878to1sl1v.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> <877f3lfzdo.fsf@skywalker.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <877f3lfzdo.fsf@skywalker.in.ibm.com> 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 "Aneesh Kumar K.V" writes: > "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 ? Considering that we have stack at the top (around 128TB) we may not be able to get a free area for such a request. But I guess the idea here is that if hint address is below 128TB, we behave as though our TASK_SIZE is 128TB ? Is that correct ? -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