Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752093AbdHHJoN (ORCPT ); Tue, 8 Aug 2017 05:44:13 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:58980 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750849AbdHHJoM (ORCPT ); Tue, 8 Aug 2017 05:44:12 -0400 Date: Tue, 8 Aug 2017 10:44:13 +0100 From: Will Deacon To: Dmitry Safonov <0x7f454c46@gmail.com> Cc: Dmitry Safonov , open list , Catalin Marinas , Russell King , linux-arm-kernel@lists.infradead.org, Cyrill Gorcunov , Pavel Emelyanov , Christopher Covington Subject: Re: [PATCH] arm64/vdso: Support mremap() for vDSO Message-ID: <20170808094413.GB13355@arm.com> References: <20170726170737.21696-1-dsafonov@virtuozzo.com> <20170728164800.GD14170@arm.com> <20170802160401.GA16932@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3319 Lines: 73 On Tue, Aug 08, 2017 at 12:29:50PM +0300, Dmitry Safonov wrote: > 2017-08-02 19:04 GMT+03:00 Will Deacon : > > On Fri, Jul 28, 2017 at 10:06:20PM +0300, Dmitry Safonov wrote: > >> 2017-07-28 19:48 GMT+03:00 Will Deacon : > >> > On Wed, Jul 26, 2017 at 08:07:37PM +0300, Dmitry Safonov wrote: > >> >> vDSO VMA address is saved in mm_context for the purpose of using > >> >> restorer from vDSO page to return to userspace after signal handling. > >> >> > >> >> In Checkpoint Restore in Userspace (CRIU) project we place vDSO VMA > >> >> on restore back to the place where it was on the dump. > >> >> With the exception for x86 (where there is API to map vDSO with > >> >> arch_prctl()), we move vDSO inherited from CRIU task to restoree > >> >> position by mremap(). > >> >> > >> >> CRIU does support arm64 architecture, but kernel doesn't update > >> >> context.vdso pointer after mremap(). Which results in translation > >> >> fault after signal handling on restored application: > >> >> https://github.com/xemul/criu/issues/288 > >> >> > >> >> Make vDSO code track the VMA address by supplying .mremap() fops > >> >> the same way it's done for x86 and arm32 by: > >> >> commit b059a453b1cf ("x86/vdso: Add mremap hook to vm_special_mapping") > >> >> commit 280e87e98c09 ("ARM: 8683/1: ARM32: Support mremap() for sigpage/vDSO"). > >> >> > >> >> Cc: Catalin Marinas > >> >> Cc: Will Deacon > >> >> Cc: Russell King > >> >> Cc: linux-arm-kernel@lists.infradead.org > >> >> Cc: Cyrill Gorcunov > >> >> Cc: Pavel Emelyanov > >> >> Cc: Christopher Covington > >> >> Signed-off-by: Dmitry Safonov > >> >> --- > >> >> arch/arm64/kernel/vdso.c | 15 +++++++++++++++ > >> >> 1 file changed, 15 insertions(+) > >> >> > >> >> diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c > >> >> index e8f759f764f2..2d419006ad43 100644 > >> >> --- a/arch/arm64/kernel/vdso.c > >> >> +++ b/arch/arm64/kernel/vdso.c > >> >> @@ -110,12 +110,27 @@ int aarch32_setup_vectors_page(struct linux_binprm *bprm, int uses_interp) > >> >> } > >> >> #endif /* CONFIG_COMPAT */ > >> >> > >> >> +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_end - vdso_start; > >> > > >> > You might be able to use vdso_pages here, but it depends on my question > >> > below. > >> > >> Yes, shifting with PAGE_SHIFT. > >> Is it just a preference? > > > > Yeah, just a minor thing, although thinking about it again, I don't know > > what you're trying to achieve with the size check anyway. Userspace is only > > going to hurt itself if it screws up the layout, so why police this? > > Well, it's for keeping the same semantics as on x86. > The idea of restriction to partial mremap() is suggested by Andy > so that userspace won't be allowed to hurt itself and to simplify > kernel code on x86. I still don't see why that's a useful thing for us to be doing on arm64, but ok. Either way: Reviewed-by: Will Deacon Will