From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f71.google.com (mail-oi0-f71.google.com [209.85.218.71]) by kanga.kvack.org (Postfix) with ESMTP id D33136B0253 for ; Thu, 7 Jul 2016 07:13:12 -0400 (EDT) Received: by mail-oi0-f71.google.com with SMTP id u81so25698950oia.3 for ; Thu, 07 Jul 2016 04:13:12 -0700 (PDT) Received: from EUR01-DB5-obe.outbound.protection.outlook.com (mail-db5eur01on0106.outbound.protection.outlook.com. [104.47.2.106]) by mx.google.com with ESMTPS id 66si1489934otm.249.2016.07.07.04.13.11 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 07 Jul 2016 04:13:12 -0700 (PDT) Subject: Re: [PATCHv2 3/6] x86/arch_prctl/vdso: add ARCH_MAP_VDSO_* References: <20160629105736.15017-1-dsafonov@virtuozzo.com> <20160629105736.15017-4-dsafonov@virtuozzo.com> From: Dmitry Safonov Message-ID: Date: Thu, 7 Jul 2016 14:11:58 +0300 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski , Michal Hocko , Vladimir Davydov Cc: "linux-kernel@vger.kernel.org" , Dmitry Safonov <0x7f454c46@gmail.com>, "linux-mm@kvack.org" , Ingo Molnar , Cyrill Gorcunov , xemul@virtuozzo.com, Oleg Nesterov , Andy Lutomirski , Thomas Gleixner , "H. Peter Anvin" , X86 ML On 07/06/2016 05:30 PM, Andy Lutomirski wrote: > On Wed, Jun 29, 2016 at 3:57 AM, Dmitry Safonov wrote: >> Add API to change vdso blob type with arch_prctl. >> As this is usefull only by needs of CRIU, expose >> this interface under CONFIG_CHECKPOINT_RESTORE. > >> +#ifdef CONFIG_CHECKPOINT_RESTORE >> + case ARCH_MAP_VDSO_X32: >> + return do_map_vdso(VDSO_X32, addr, false); >> + case ARCH_MAP_VDSO_32: >> + return do_map_vdso(VDSO_32, addr, false); >> + case ARCH_MAP_VDSO_64: >> + return do_map_vdso(VDSO_64, addr, false); >> +#endif >> + > > This will have an odd side effect: if the old mapping is still around, > its .fault will start behaving erratically. I wonder if we can either > reliably zap the old vma (or check that it's not there any more) > before mapping a new one or whether we can associate the vdso image > with the vma (possibly by having a separate vm_special_mapping for > each vdso_image. The latter is quite easy: change vdso_image to embed > vm_special_mapping and use container_of in vdso_fault to fish the > vdso_image back out. But we'd have to embed another > vm_special_mapping for the vvar mapping as well for the same reason. > > I'm also a bit concerned that __install_special_mapping might not get > all the cgroup and rlimit stuff right. If we ensure that any old > mappings are gone, then the damage is bounded, but otherwise someone > might call this in a loop and fill their address space with arbitrary > numbers of special mappings. Well, I have deleted code that unmaps old vdso because I didn't saw a reason why it's bad and wanted to reduce code. But well, now I do see reasons, thanks. Hmm, what do you think if I do it a little different way then embedding vm_special_mapping: just that old hack with vma_ops. If I add a close() hook there and make there context.vdso = NULL pointer, then I can test it on remap. This can also have nice feature as restricting partial munmap of vdso blob. Is this sounds sane? -- 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