Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755862AbaFYVFu (ORCPT ); Wed, 25 Jun 2014 17:05:50 -0400 Received: from mail-la0-f53.google.com ([209.85.215.53]:63257 "EHLO mail-la0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754214AbaFYVFt (ORCPT ); Wed, 25 Jun 2014 17:05:49 -0400 MIME-Version: 1.0 In-Reply-To: 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> <9E0BE1322F2F2246BD820DA9FC397ADE016AF41C@shsmsx102.ccr.corp.intel.com> <9E0BE1322F2F2246BD820DA9FC397ADE016B26AB@shsmsx102.ccr.corp.intel.com> From: Andy Lutomirski Date: Wed, 25 Jun 2014 14:05:27 -0700 Message-ID: Subject: Re: [PATCH v6 02/10] x86, mpx: add MPX specific mmap interface To: "Ren, Qiaowei" Cc: "Hansen, Dave" , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , X86 ML , "linux-kernel@vger.kernel.org" , Linux MM Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 25, 2014 at 2:04 PM, Andy Lutomirski wrote: > On Tue, Jun 24, 2014 at 6:40 PM, Ren, Qiaowei wrote: >> On 2014-06-25, Andy Lutomirski wrote: >>> On Mon, Jun 23, 2014 at 10:53 PM, Ren, Qiaowei >>> wrote: >>>> 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? >>> >>> Does this actually create a vma backed with real memory? Doesn't this >>> need to go through anon_vma or something? _install_special_mapping >>> completely prevents merging. >>> >> Hmm, _install_special_mapping should completely prevent merging, even among MPX vmas. >> >> So, could you tell me how to set MPX specific ->name to the vma when it is created? Seems like that I could not find such interface. > > You may need to add one. > > I'd suggest posting a new thread to linux-mm describing what you need > and asking how to do it. Hmm. the memfd_create thing may be able to do this for you. If you created a per-mm memfd and mapped it, it all just might work. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/