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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT autolearn=unavailable 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 6FB9CC48BE2 for ; Thu, 20 Jun 2019 09:22:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3AD3221530 for ; Thu, 20 Jun 2019 09:22:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561022534; bh=NVni3K2b6jaPXcel1tuSet44zE5dh2fJlgDNT+h/Ugs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=QtsOMhTNmHA9Zv7oU1e88asDmGcSJ68F5AeQg+6ADKkJPZMkbIN26HWJjVHC9LKrR vDwI3vs3aVZSVbm6tYzFJgqY2qVEsSj3Qk//OKmmJHL07iW4C/wEkvnrxH1Y37fjKw JPVgvVoxq+oTZVFPxNySdTBezE6ahK15JLyux1pM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730568AbfFTJWN (ORCPT ); Thu, 20 Jun 2019 05:22:13 -0400 Received: from mx2.suse.de ([195.135.220.15]:45652 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725875AbfFTJWM (ORCPT ); Thu, 20 Jun 2019 05:22:12 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 1AA10AF58; Thu, 20 Jun 2019 09:22:11 +0000 (UTC) Date: Thu, 20 Jun 2019 11:22:09 +0200 From: Michal Hocko To: Minchan Kim Cc: Andrew Morton , linux-mm , LKML , linux-api@vger.kernel.org, Johannes Weiner , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Daniel Colascione , Shakeel Butt , Sonny Rao , Brian Geffon , jannh@google.com, oleg@redhat.com, christian@brauner.io, oleksandr@redhat.com, hdanton@sina.com, lizeb@google.com Subject: Re: [PATCH v2 4/5] mm: introduce MADV_PAGEOUT Message-ID: <20190620092209.GD12083@dhcp22.suse.cz> References: <20190610111252.239156-1-minchan@kernel.org> <20190610111252.239156-5-minchan@kernel.org> <20190619132450.GQ2968@dhcp22.suse.cz> <20190620041620.GB105727@google.com> <20190620070444.GB12083@dhcp22.suse.cz> <20190620084040.GD105727@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190620084040.GD105727@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 20-06-19 17:40:40, Minchan Kim wrote: > > > > Pushing out a shared page cache > > > > is possible even now but this interface gives a much easier tool to > > > > evict shared state and perform all sorts of timing attacks. Unless I am > > > > missing something we should be doing something similar to mincore and > > > > ignore shared pages without a writeable access or at least document why > > > > we do not care. > > > > > > I'm not sure IIUC side channel attach. As you mentioned, without this syscall, > > > 1. they already can do that simply by memory hogging > > > > This is way much more harder for practical attacks because the reclaim > > logic is not fully under the attackers control. Having a direct tool to > > reclaim memory directly then just opens doors to measure the other > > consumers of that memory and all sorts of side channel. > > Not sure it's much more harder. It's really easy on my experience. > Just creating new memory hogger and consume memory step by step until > you newly allocated pages will be reclaimed. You can contain an untrusted application into a memcg and it will only reclaim its own working set. > > > 2. If we need fix MADV_PAGEOUT, that means we need to fix MADV_DONTNEED, too? > > > > nope because MADV_DONTNEED doesn't unmap from other processes. > > Hmm, I don't understand. MADV_PAGEOUT doesn't unmap from other > processes, either. Either I am confused or missing something. shrink_page_list does try_to_unmap and that unmaps from all processes, right? > Could you elborate it a bit more what's your concern? If you manage to unmap from a remote process then you can measure delays implied from the refault and that information can be used to infer what the remote application is doing. -- Michal Hocko SUSE Labs