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=-2.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,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 EE8D0C2BB1D for ; Tue, 17 Mar 2020 15:01:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BE7EB20735 for ; Tue, 17 Mar 2020 15:01:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584457261; bh=qozp4mAmk80/dw66b2ODzgKhXyNgiGnEZxLweGXrNTE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=qXQOkLP4Z28SxMWcwkAf8H3lX+Mz2bv+Cy/bfVYs5gKbyftbOg00F2U2Q3lLDczU5 yN5gzzm1Ney54kyuacLtsRpQ88u1yPQkrYQRIDXgKyn11rlBqdfNrKEsshQH8QLGUB IictnsqFyk6naBrE4V3qImfQtoGj3mGQjiZqYNjY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726761AbgCQPBA (ORCPT ); Tue, 17 Mar 2020 11:01:00 -0400 Received: from mail-pl1-f182.google.com ([209.85.214.182]:33476 "EHLO mail-pl1-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726478AbgCQPBA (ORCPT ); Tue, 17 Mar 2020 11:01:00 -0400 Received: by mail-pl1-f182.google.com with SMTP id ay11so9747615plb.0 for ; Tue, 17 Mar 2020 08:00:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=vfSoAVJlByohpySolMWfb+lAbCe6QR2JwcgA3eLHp8k=; b=Yr7bXDAjHvpERe5gNP7DKJVrpgmoZtqpYYfjAX+Ve79pomZJlKPGBG1KqYfkzXXV4/ YU+mnGOKksoOhyt6t3j+y4EtEbsHUNvCzvLA1DklrigBAULWUGyO2T4dJRDR9X0lrOnb RQ7m87LlJuDdekWSSo0GmPvusnYxhEbuN+Ae3wTyXIMwcjKtywVIprXeJvb+XCvcx1A9 bjFSt3C5rUbUtRO7AMOhJgPfreUCfQNmpj9vyJKB79EjWGYpnxA909FagV4kxJ547QXp /NDQ4iv8nvDajf/gI0QieYcfNXD6IFGHaNoQy95WM9sWBXHo2IpFH/JkGNE5gQERDoeL Mo6w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=vfSoAVJlByohpySolMWfb+lAbCe6QR2JwcgA3eLHp8k=; b=PficZGg5WjRjI5TAvsl3wGmb93wWYHCdTnH/1a2IxXTNT4rhG1i1KSs/wKTGaWvIMJ zkKxT8jnpVBWF0O3CNxr0vtvBg45l39oBnhpW1NwxBvK6YZbOxolxZXWQpezrNxbhJ2T 3kH0WlJ3Sxj3Bn/9sZsfMTwscskgKG1a4QOrKt793WnJPldd62AGcsAHMX3W1dUBHwBP maflROrk7pbn0+gtpOO58NqirvL57zQZUHVKFuEDgBHZflINW5kLEmiFgdRguP7HPcES kKojbq2jwipZJCV35kALTtt9QNJ+4lSwXgy0n13Irq6z0bsdMfI86TxNY/xGOOWz7sUG Cpcw== X-Gm-Message-State: ANhLgQ0iEHJ3pe/EeDee7J0Uh2uHNeYkMLX2IdfnEkZiF7iohF4WzEt1 h281gIpGWh3eWWbo8hYhhoo= X-Google-Smtp-Source: ADFU+vsSMRYG+5Cr2foBfrD9eVKu86uVo7HHockEOoT/ujyxOB6x5/FjJ1fmLdLJ39mUyEtNaCIFtw== X-Received: by 2002:a17:90a:feb:: with SMTP id 98mr5798277pjz.72.1584457258142; Tue, 17 Mar 2020 08:00:58 -0700 (PDT) Received: from google.com ([2620:15c:211:1:3e01:2939:5992:52da]) by smtp.gmail.com with ESMTPSA id d1sm3437488pfc.3.2020.03.17.08.00.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Mar 2020 08:00:56 -0700 (PDT) Date: Tue, 17 Mar 2020 08:00:55 -0700 From: Minchan Kim To: Michal Hocko Cc: Jann Horn , Linux-MM , kernel list , Daniel Colascione , Dave Hansen , "Joel Fernandes (Google)" , Andrew Morton Subject: Re: interaction of MADV_PAGEOUT with CoW anonymous mappings? Message-ID: <20200317150055.GC73302@google.com> References: <20200312082248.GS23944@dhcp22.suse.cz> <20200312201602.GA68817@google.com> <20200312204155.GE23944@dhcp22.suse.cz> <20200313020851.GD68817@google.com> <20200313080546.GA21007@dhcp22.suse.cz> <20200313205941.GA78185@google.com> <20200316092052.GD11482@dhcp22.suse.cz> <20200317014340.GA73302@google.com> <20200317071239.GB26018@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200317071239.GB26018@dhcp22.suse.cz> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 17, 2020 at 08:12:39AM +0100, Michal Hocko wrote: > On Mon 16-03-20 18:43:40, Minchan Kim wrote: > > On Mon, Mar 16, 2020 at 10:20:52AM +0100, Michal Hocko wrote: > > > On Fri 13-03-20 13:59:41, Minchan Kim wrote: > > > > On Fri, Mar 13, 2020 at 09:05:46AM +0100, Michal Hocko wrote: > > > > > On Thu 12-03-20 19:08:51, Minchan Kim wrote: > > > > > > On Thu, Mar 12, 2020 at 09:41:55PM +0100, Michal Hocko wrote: > > > > > > > On Thu 12-03-20 13:16:02, Minchan Kim wrote: > > > > > > > > On Thu, Mar 12, 2020 at 09:22:48AM +0100, Michal Hocko wrote: > > > > > > > [...] > > > > > > > > > From eca97990372679c097a88164ff4b3d7879b0e127 Mon Sep 17 00:00:00 2001 > > > > > > > > > From: Michal Hocko > > > > > > > > > Date: Thu, 12 Mar 2020 09:04:35 +0100 > > > > > > > > > Subject: [PATCH] mm: do not allow MADV_PAGEOUT for CoW pages > > > > > > > > > > > > > > > > > > Jann has brought up a very interesting point [1]. While shared pages are > > > > > > > > > excluded from MADV_PAGEOUT normally, CoW pages can be easily reclaimed > > > > > > > > > that way. This can lead to all sorts of hard to debug problems. E.g. > > > > > > > > > performance problems outlined by Daniel [2]. There are runtime > > > > > > > > > environments where there is a substantial memory shared among security > > > > > > > > > domains via CoW memory and a easy to reclaim way of that memory, which > > > > > > > > > MADV_{COLD,PAGEOUT} offers, can lead to either performance degradation > > > > > > > > > in for the parent process which might be more privileged or even open > > > > > > > > > side channel attacks. The feasibility of the later is not really clear > > > > > > > > > > > > > > > > I am not sure it's a good idea to mention performance stuff because > > > > > > > > it's rather arguble. You and Johannes already pointed it out when I sbumit > > > > > > > > early draft which had shared page filtering out logic due to performance > > > > > > > > reason. You guys suggested the shared pages has higher chance to be touched > > > > > > > > so that if it's really hot pages, that whould keep in the memory. I agree. > > > > > > > > > > > > > > Yes, the hot memory is likely to be referenced but the point was an > > > > > > > unexpected latency because of the major fault. I have to say that I have > > > > > > > > > > > > I don't understand your point here. If it's likely to be referenced > > > > > > among several processes, it doesn't have the major fault latency. > > > > > > What's your point here? > > > > > > > > > > a) the particular CoW page might be cold enough to be reclaimed and b) > > > > > > > > If it is, that means it's *cold* so it's really worth to be reclaimed. > > > > > > > > > nothing really prevents the MADV_PAGEOUT to be called faster than the > > > > > reference bit being readded. > > > > > > > > Yeb, that's undesirable. I should admit it was not intended when I implemented > > > > PAGEOUT. The thing is page_check_references clears access bit of pte for every > > > > process are sharing the page so that two times MADV_PAGEOUT from a process could > > > > evict the page. That's the really bug. > > > > > > I do not really think this is a bug. This is a side effect of the > > > reclaim process and we do not really want MADV_{PAGEOUT,COLD} behave > > > > No, that's the bug since we didn't consider the side effect. > > > > > differently here because then the behavior would be even harder to > > > > No, I do want to have difference because it's per-process hint. IOW, > > what he know is for only his context, not others so it shouldn't clean > > others' pte. That makes difference between LRU aging and the hint. > > Just to make it clear, are you really suggesting to special case > page_check_references for madvise path? > No, (page_mapcount() > 1) checks *effectively* fixes the performance bug as well as vulnerability issue.