From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f48.google.com (mail-wg0-f48.google.com [74.125.82.48]) by kanga.kvack.org (Postfix) with ESMTP id 25D5A6B0035 for ; Tue, 20 May 2014 14:28:12 -0400 (EDT) Received: by mail-wg0-f48.google.com with SMTP id b13so920932wgh.19 for ; Tue, 20 May 2014 11:28:11 -0700 (PDT) Received: from mail.zytor.com (terminus.zytor.com. [2001:1868:205::10]) by mx.google.com with ESMTPS id cf2si13706244wjc.124.2014.05.20.11.28.05 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 20 May 2014 11:28:06 -0700 (PDT) Message-ID: <537B9EA6.3030103@zytor.com> Date: Tue, 20 May 2014 11:27:50 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 Subject: Re: [PATCH 3/4] x86,mm: Improve _install_special_mapping and fix x86 vdso naming References: <276b39b6b645fb11e345457b503f17b83c2c6fd0.1400538962.git.luto@amacapital.net> <20140520172134.GJ2185@moon> <20140520174759.GK2185@moon> <20140520180104.GL2185@moon> <537B9C6D.7010705@zytor.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski Cc: Cyrill Gorcunov , X86 ML , Andrew Morton , Sasha Levin , "linux-mm@kvack.org" , Dave Jones , LKML , Pavel Emelyanov On 05/20/2014 11:24 AM, Andy Lutomirski wrote: > On Tue, May 20, 2014 at 11:18 AM, H. Peter Anvin wrote: >> On 05/20/2014 11:01 AM, Cyrill Gorcunov wrote: >>>> >>>> This patch should fix this issue, at least. If there's still a way to >>>> get a native vdso that doesn't say "[vdso]", please let me know/ >>> >>> Yes, having a native procfs way to detect vdso is much preferred! >>> >> >> Is there any path by which we can end up with [vdso] without a leading >> slash in /proc/self/maps? Otherwise, why is that not "native"? > > Dunno. But before this patch the reverse was possible: we can end up > with a vdso that doesn't say [vdso]. > That's a bug, which is being fixed. We can't go back in time and create new interfaces on old kernels. >> >>>>> The situation get worse when task was dumped on one kernel and >>>>> then restored on another kernel where vdso content is different >>>>> from one save in image -- is such case as I mentioned we need >>>>> that named vdso proxy which redirect calls to vdso of the system >>>>> where task is restoring. And when such "restored" task get checkpointed >>>>> second time we don't dump new living vdso but save only old vdso >>>>> proxy on disk (detecting it is a different story, in short we >>>>> inject a unique mark into elf header). >>>> >>>> Yuck. But I don't know whether the kernel can help much here. >>> >>> Some prctl which would tell kernel to put vdso at specifed address. >>> We can live without it for now so not a big deal (yet ;) >> >> mremap() will do this for you. > > Except that it's buggy: it doesn't change mm->context.vdso. For > 64-bit tasks, the only consumer outside exec was arch_vma_name, and > this patch removes even that. For 32-bit tasks, though, it's needed > for signal delivery. > Again, a bug, let's fix it rather than saying we need a new interface. -hpa -- 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