From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 3B8C16B0038 for ; Mon, 7 Nov 2016 13:23:55 -0500 (EST) Received: by mail-pf0-f200.google.com with SMTP id y68so54408508pfb.6 for ; Mon, 07 Nov 2016 10:23:55 -0800 (PST) Received: from EUR02-HE1-obe.outbound.protection.outlook.com (mail-eopbgr10111.outbound.protection.outlook.com. [40.107.1.111]) by mx.google.com with ESMTPS id 190si20424646pga.53.2016.11.07.10.16.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 07 Nov 2016 10:16:21 -0800 (PST) Subject: Re: [PATCH] arm/vdso: introduce vdso_mremap hook References: <20161101172214.2938-1-dsafonov@virtuozzo.com> <0b41c28b-20ef-332f-d8d6-e381e05b8252@codeaurora.org> <714d2aea-ed4c-6272-89c1-e1d0e037855e@virtuozzo.com> From: Dmitry Safonov Message-ID: Date: Mon, 7 Nov 2016 21:13:22 +0300 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Christopher Covington , linux-kernel@vger.kernel.org Cc: 0x7f454c46@gmail.com, Kevin Brodsky , Andy Lutomirski , Oleg Nesterov , Russell King , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, Cyrill Gorcunov , Pavel Emelyanov , Nathan Lynch , Michael Ellerman On 11/07/2016 09:08 PM, Christopher Covington wrote: > On 11/07/2016 12:16 PM, Dmitry Safonov wrote: >> On 11/07/2016 08:00 PM, Christopher Covington wrote: >>> Hi Dmitry, >>> >>> On 11/01/2016 01:22 PM, Dmitry Safonov wrote: >>>> Add vdso_mremap hook which will fix context.vdso pointer after mremap() >>>> on vDSO vma. This is needed for correct landing after syscall execution. >>>> Primary goal of this is for CRIU on arm - we need to restore vDSO image >>>> at the exactly same place where the vma was in dumped application. With >>>> the help of this hook we'll move vDSO at the new position. >>>> The CRIU code handles situations like when vDSO of dumped application >>>> was different from vDSO on restoring system. This usally happens when >>>> some new symbols are being added to vDSO. In these situations CRIU >>>> inserts jump trampolines from old vDSO blob to new vDSO on restore. >>>> By that reason even if on restore vDSO blob lies on the same address as >>>> blob in dumped application - we still need to move it if it differs. >>>> >>>> There was previously attempt to add this functionality for arm64 by >>>> arch_mremap hook [1], while this patch introduces this with minimal >>>> effort - the same way I've added it to x86: >>>> commit b059a453b1cf ("x86/vdso: Add mremap hook to vm_special_mapping") >>>> >>>> At this moment, vdso restoring code is disabled for arm/arm64 arch >>>> in CRIU [2], so C/R is only working for !CONFIG_VDSO kernels. This patch >>>> is aimed to fix that. >>>> The same hook may be introduced for arm64 kernel, but at this moment >>>> arm64 vdso code is actively reworked by Kevin, so we can do it on top. >>>> Separately, I've refactored arch_remap hook out from ppc64 [3]. >>>> >>>> [1]: https://marc.info/?i=1448455781-26660-1-git-send-email-cov@codeaurora.org >>>> [2]: https://github.com/xemul/criu/blob/master/Makefile#L39 >>>> [3]: https://marc.info/?i=20161027170948.8279-1-dsafonov@virtuozzo.com >>>> >>>> Cc: Kevin Brodsky >>>> Cc: Christopher Covington >>>> Cc: Andy Lutomirski >>>> Cc: Oleg Nesterov >>>> Cc: Russell King >>>> Cc: Will Deacon >>>> Cc: linux-arm-kernel@lists.infradead.org >>>> Cc: linux-mm@kvack.org >>>> Cc: Cyrill Gorcunov >>>> Cc: Pavel Emelyanov >>>> Signed-off-by: Dmitry Safonov >>>> --- >>>> arch/arm/kernel/vdso.c | 21 +++++++++++++++++++++ >>>> 1 file changed, 21 insertions(+) >>>> >>>> diff --git a/arch/arm/kernel/vdso.c b/arch/arm/kernel/vdso.c >>>> index 53cf86cf2d1a..d1001f87c2f6 100644 >>>> --- a/arch/arm/kernel/vdso.c >>>> +++ b/arch/arm/kernel/vdso.c >>>> @@ -54,8 +54,11 @@ static const struct vm_special_mapping vdso_data_mapping = { >>>> .pages = &vdso_data_page, >>>> }; >>>> >>>> +static int vdso_mremap(const struct vm_special_mapping *sm, >>>> + struct vm_area_struct *new_vma); >>>> static struct vm_special_mapping vdso_text_mapping __ro_after_init = { >>>> .name = "[vdso]", >>>> + .mremap = vdso_mremap, >>>> }; >>>> >>>> struct elfinfo { >>>> @@ -254,6 +257,24 @@ void arm_install_vdso(struct mm_struct *mm, unsigned long addr) >>>> mm->context.vdso = addr; >>>> } >>>> >>>> +static int vdso_mremap(const struct vm_special_mapping *sm, >>>> + struct vm_area_struct *new_vma) >>>> +{ >>>> + unsigned long new_size = new_vma->vm_end - new_vma->vm_start; >>>> + unsigned long vdso_size = (vdso_total_pages - 1) << PAGE_SHIFT; >>>> + >>>> + /* Disallow partial vDSO blob remap */ >>>> + if (vdso_size != new_size) >>>> + return -EINVAL; >>>> + >>>> + if (WARN_ON_ONCE(current->mm != new_vma->vm_mm)) >>>> + return -EFAULT; >>>> + >>>> + current->mm->context.vdso = new_vma->vm_start; >>>> + >>>> + return 0; >>>> +} >>>> + >>>> static void vdso_write_begin(struct vdso_data *vdata) >>>> { >>>> ++vdso_data->seq_count; >>>> >>> >>> What do you think about putting this code somewhere generic (not under >>> arch/*), so that powerpc and arm64 can reuse it once the cosmetic changes >>> to make them compatible are made? My thought was that it could be defined >>> underneath CONFIG_GENERIC_VDSO, which architectures could select as they >>> became compatible. >> >> Hi Chistopher, >> >> Well, I don't think we won something out of generalization of simple assignment for context.vdso pointer accross arches. And a need to rename >> vdso over arches for saving one single line? > > I count 17 lines, which duplicated across 3 architectures becomes 51 lines. > Presumable in the future other architectures will want CRIU support as well. > Additionally, should fixes ever be required, fixing one implementation instead > of 3+ is preferred. > >> Also I don't like a bit this arch_mremap hook and need to nullify >> vdso pointer. > > I'm sorry for the confusion but I in no way meant to imply that the > arch_mremap hook should be carried forward. I fully agree that the function > pointer in struct vm_special_mapping is the better way to go. > > If you don't want to implement a version with vdso_mremap defined in a > generic location (using it from struct vm_special_mapping), do you mind if I > propose such a version? Sure, do it, no objections. -- Dmitry -- 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