From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A306CC433E1 for ; Fri, 24 Jul 2020 14:42:03 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6B5582065F for ; Fri, 24 Jul 2020 14:42:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="zjcguEGZ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6B5582065F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=GqjkG5E11GZ4nnUzI/Klc11/MD6xoWopEdQszjlPpNg=; b=zjcguEGZB3o6wL9+3/SuYS9ro D8/B0KOClmXuq3dSiVi6zGTfH5245Q+MMBxjrx6fRKzKaya7K5Rfky0jgKZlyy8lvp6ToJI8hDsk7 LHfAqyh5IUrNL4CEVhon5vQZX6D4wEthxH1kuOihdCkPHfoZYZ8K+mocbLFD3NqdF0avfCxZ8GC/j 7M/UVFD4Uf1KGeL7S+hVSj/m7GU/+zJPgs3eq0fSRbA7flCGfdKo2XADMFBM3B+DIW+fiTllS3iVW ha+yQ+bT7sluZ2Zppr5LjQ6XaPmuHjGqXJ2r8ybi//muGwuJKBkGZayniKb77LfNPiclb98QJYEfB +h2I4gtGw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jyysI-0005Kv-U4; Fri, 24 Jul 2020 14:40:38 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jyysD-0005Gz-Gj for linux-arm-kernel@lists.infradead.org; Fri, 24 Jul 2020 14:40:34 +0000 Received: from gaia (unknown [95.146.230.158]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AF3862063A; Fri, 24 Jul 2020 14:40:30 +0000 (UTC) Date: Fri, 24 Jul 2020 15:40:28 +0100 From: Catalin Marinas To: Christian Brauner Subject: Re: [PATCH v5 0/6] arm64: add the time namespace support Message-ID: <20200724144027.GE23388@gaia> References: <20200624083321.144975-1-avagin@gmail.com> <20200705064055.GA28894@gmail.com> <20200714015743.GA843937@gmail.com> <20200722181506.GA4517@gaia> <20200723174140.GA3991167@gmail.com> <20200724133039.hginkpnv7bkyz764@wittgenstein> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200724133039.hginkpnv7bkyz764@wittgenstein> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200724_104033_731367_4BED5D47 X-CRM114-Status: GOOD ( 41.63 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Dmitry Safonov , linux-kernel@vger.kernel.org, Andrei Vagin , Thomas Gleixner , Vincenzo Frascino , Will Deacon , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Jul 24, 2020 at 03:30:39PM +0200, Christian Brauner wrote: > On Thu, Jul 23, 2020 at 10:41:40AM -0700, Andrei Vagin wrote: > > On Wed, Jul 22, 2020 at 07:15:06PM +0100, Catalin Marinas wrote: > > > On Mon, Jul 13, 2020 at 06:57:43PM -0700, Andrei Vagin wrote: > > > > On Sat, Jul 04, 2020 at 11:40:55PM -0700, Andrei Vagin wrote: > > > > > On Wed, Jun 24, 2020 at 01:33:15AM -0700, Andrei Vagin wrote: > > > > > > Allocate the time namespace page among VVAR pages and add the logic > > > > > > to handle faults on VVAR properly. > > > > > > > > > > > > If a task belongs to a time namespace then the VVAR page which contains > > > > > > the system wide VDSO data is replaced with a namespace specific page > > > > > > which has the same layout as the VVAR page. That page has vdso_data->seq > > > > > > set to 1 to enforce the slow path and vdso_data->clock_mode set to > > > > > > VCLOCK_TIMENS to enforce the time namespace handling path. > > > > > > > > > > > > The extra check in the case that vdso_data->seq is odd, e.g. a concurrent > > > > > > update of the VDSO data is in progress, is not really affecting regular > > > > > > tasks which are not part of a time namespace as the task is spin waiting > > > > > > for the update to finish and vdso_data->seq to become even again. > > > > > > > > > > > > If a time namespace task hits that code path, it invokes the corresponding > > > > > > time getter function which retrieves the real VVAR page, reads host time > > > > > > and then adds the offset for the requested clock which is stored in the > > > > > > special VVAR page. > > > > > > > > > > > > > > > > > v2: Code cleanups suggested by Vincenzo. > > > > > > v3: add a comment in __arch_get_timens_vdso_data. > > > > > > v4: - fix an issue reported by the lkp robot. > > > > > > - vvar has the same size with/without CONFIG_TIME_NAMESPACE, but the > > > > > > timens page isn't allocated on !CONFIG_TIME_NAMESPACE. This > > > > > > simplifies criu/vdso migration between different kernel configs. > > > > > > v5: - Code cleanups suggested by Mark Rutland. > > > > > > - In vdso_join_timens, mmap_write_lock is downgraded to > > > > > > mmap_read_lock. The VMA list isn't changed there, zap_page_range > > > > > > doesn't require mmap_write_lock. > > > > > > > > > > > > Reviewed-by: Vincenzo Frascino > > > > > > Reviewed-by: Dmitry Safonov > > > > > > > > > > Hello Will and Catalin, > > > > > > > > > > Have you had a chance to look at this patch set? I think it is ready to be > > > > > merged. Let me know if you have any questions. > > > > > > > > *friendly ping* > > > > > > > > If I am doing something wrong, let me know. > > > > > > Not really, just haven't got around to looking into it. Mark Rutland > > > raised a concern (in private) about the safety of multithreaded apps > > > but I think you already replied that timens_install() checks for this > > > already [1]. > > > > > > Maybe a similar atomicity issue to the one raised by Mark but for > > > single-threaded processes: the thread is executing vdso code, gets > > > interrupted and a signal handler invokes setns(). Would resuming the > > > execution in the vdso code on sigreturn cause any issues? > > > > It will not cause any issues in the kernel. In the userspace, > > clock_gettime() can return a clock value with an inconsistent offset, if > > a process switches between two non-root namespaces. And it can triggers > > SIGSEGV if it switches from a non-root to the root time namespace, > > because a time namespace isn't mapped in the root time namespace. > > > > I don't think that we need to handle this case in the kernel. Users > > must understand what they are doing and have to write code so that avoid > > these sort of situations. In general, I would say that in most cases it > > is a bad idea to call setns from a signal handler. > > I would argue that calling any function not in the list of > man 7 signal-safety > without checking the kernel implementation is "you get to keep the > pieces territory". There's a whole range of syscalls that are not safe > in signal handlers and we don't have any special precautions for them so > I'm not sure we'd need one for setns(). But maybe I'm missing the bigger > picture here. Good point (I don't read man pages very often ;)). Thanks for clarifying. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel