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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:38342 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752132AbdCSP2v (ORCPT ); Sun, 19 Mar 2017 11:28:51 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v2J8reba000448 for ; Sun, 19 Mar 2017 04:56:12 -0400 Received: from e23smtp08.au.ibm.com (e23smtp08.au.ibm.com [202.81.31.141]) by mx0b-001b2d01.pphosted.com with ESMTP id 29911p0th0-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Sun, 19 Mar 2017 04:56:12 -0400 Received: from localhost by e23smtp08.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sun, 19 Mar 2017 18:56:09 +1000 From: "Aneesh Kumar K.V" 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 Message-ID: <878to1sl1v.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: <20170319085508.iPfaNWB6WLV8-QyMPHANZGsZlYCT-BP98kbZT32BWJc@z> "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