Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751845AbaFXF6T (ORCPT ); Tue, 24 Jun 2014 01:58:19 -0400 Received: from mga11.intel.com ([192.55.52.93]:52866 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751155AbaFXF6R (ORCPT ); Tue, 24 Jun 2014 01:58:17 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.01,536,1400050800"; d="scan'208";a="552373529" From: "Ren, Qiaowei" To: Andy Lutomirski , "Hansen, Dave" CC: "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , X86 ML , "linux-kernel@vger.kernel.org" , Linux MM Subject: RE: [PATCH v6 02/10] x86, mpx: add MPX specific mmap interface Thread-Topic: [PATCH v6 02/10] x86, mpx: add MPX specific mmap interface Thread-Index: AQHPitp0g7xixZVNTkiLN9tFeBCqMZt+nJAAgAAD+ACAAADtgIAABhEAgAAKEgCAARYTkA== Date: Tue, 24 Jun 2014 05:53:46 +0000 Message-ID: <9E0BE1322F2F2246BD820DA9FC397ADE016AF41C@shsmsx102.ccr.corp.intel.com> References: <1403084656-27284-1-git-send-email-qiaowei.ren@intel.com> <1403084656-27284-3-git-send-email-qiaowei.ren@intel.com> <53A884B2.5070702@mit.edu> <53A88806.1060908@intel.com> <53A88DE4.8050107@intel.com> In-Reply-To: Accept-Language: zh-CN, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.239.127.40] Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by mail.home.local id s5O5wTim025211 On 2014-06-24, Andy Lutomirski wrote: >> On 06/23/2014 01:06 PM, Andy Lutomirski wrote: >>> Can the new vm_operation "name" be use for this? The magic "always >>> written to core dumps" feature might need to be reconsidered. >> >> One thing I'd like to avoid is an MPX vma getting merged with a >> non-MPX vma. I don't see any code to prevent two VMAs with >> different vm_ops->names from getting merged. That seems like a bit >> of a design oversight for ->name. Right? > > AFAIK there are no ->name users that don't also set ->close, for > exactly that reason. I'd be okay with adding a check for ->name, too. > > Hmm. If MPX vmas had a real struct file attached, this would all come > for free. Maybe vmas with non-default vm_ops and file != NULL should > never be mergeable? > >> >> Thinking out loud a bit... There are also some more complicated but >> more performant cleanup mechanisms that I'd like to go after in the future. >> Given a page, we might want to figure out if it is an MPX page or not. >> I wonder if we'll ever collide with some other user of vm_ops->name. >> It looks fairly narrowly used at the moment, but would this keep us >> from putting these pages on, say, a tmpfs mount? Doesn't look that >> way at the moment. > > You could always check the vm_ops pointer to see if it's MPX. > > One feature I've wanted: a way to have special per-process vmas that > can be easily found. For example, I want to be able to efficiently > find out where the vdso and vvar vmas are. I don't think this is currently supported. > Andy, if you add a check for ->name to avoid the MPX vmas merged with non-MPX vmas, I guess the work flow should be as follow (use _install_special_mapping to get a new vma): unsigned long mpx_mmap(unsigned long len) { ...... static struct vm_special_mapping mpx_mapping = { .name = "[mpx]", .pages = no_pages, }; ....... vma = _install_special_mapping(mm, addr, len, vm_flags, &mpx_mapping); ...... } Then, we could check the ->name to see if the VMA is MPX specific. Right? Thanks, Qiaowei ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m???? ????????I?