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=-1.0 required=3.0 tests=MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 989EFC2BB1D for ; Fri, 13 Mar 2020 08:05:52 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 633B1206E2 for ; Fri, 13 Mar 2020 08:05:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 633B1206E2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D9F436B0005; Fri, 13 Mar 2020 04:05:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D76AA6B0006; Fri, 13 Mar 2020 04:05:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CB3A36B0007; Fri, 13 Mar 2020 04:05:51 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0087.hostedemail.com [216.40.44.87]) by kanga.kvack.org (Postfix) with ESMTP id B211A6B0005 for ; Fri, 13 Mar 2020 04:05:51 -0400 (EDT) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 7E42E180AD806 for ; Fri, 13 Mar 2020 08:05:51 +0000 (UTC) X-FDA: 76589605302.23.ring08_6d4db1a7c7229 X-HE-Tag: ring08_6d4db1a7c7229 X-Filterd-Recvd-Size: 5528 Received: from mail-wr1-f66.google.com (mail-wr1-f66.google.com [209.85.221.66]) by imf47.hostedemail.com (Postfix) with ESMTP for ; Fri, 13 Mar 2020 08:05:51 +0000 (UTC) Received: by mail-wr1-f66.google.com with SMTP id x11so6084631wrv.5 for ; Fri, 13 Mar 2020 01:05:50 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=FQIOitXv3I5pRGgA4gJJvh9qLRp63SkIhEeNZmb4v4Y=; b=udMXBhth2RWzZ40MCFh273gJvrOjZEjB/e72Q9asnuSrx7XjAGE4zUWblWM95Fa6aL 9/Wdo4R6/klQiBDhk8bnPW9riI+mchr8H/4C/0+AJzlB0yvF6Tb2SkdJTvV3VaHk6B+6 DUOjlQFjkFU4XvknzD522HRnwhrObXGqfl7yDm2WIBu9ht/Oyj7XJ3MCnjE93kN0B2Xj +ed+UKvBPOHG2LyNLpQBmAJWXGW8C67Io99cDKCDVmWqr82lzF/E3AO2TMGB9X546t6o 1Oaq+w/EAlgUnVcNIqox1wY+2plseDvPzqOnOcy8AKQi/tI5exouSDgEJIWXtTTwPjxJ /kmQ== X-Gm-Message-State: ANhLgQ2vO/MUpRHSGzQ5AfIdVfujbDM8qtB0W/ZcD5qAFuwzCyGIhIsS AoJf+1PJejUhqEjWhSs+xM8= X-Google-Smtp-Source: ADFU+vtTyV3NvKc+L2hMQ/BBBqjMU3ksdfo2QGEY4XxgRncswglhQHcuaxtLB7TyTXalsxzeF1WkFA== X-Received: by 2002:a5d:6150:: with SMTP id y16mr16406894wrt.352.1584086749914; Fri, 13 Mar 2020 01:05:49 -0700 (PDT) Received: from localhost (ip-37-188-247-35.eurotel.cz. [37.188.247.35]) by smtp.gmail.com with ESMTPSA id 133sm16541367wmd.5.2020.03.13.01.05.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Mar 2020 01:05:49 -0700 (PDT) Date: Fri, 13 Mar 2020 09:05:46 +0100 From: Michal Hocko To: Minchan Kim 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: <20200313080546.GA21007@dhcp22.suse.cz> References: <20200312082248.GS23944@dhcp22.suse.cz> <20200312201602.GA68817@google.com> <20200312204155.GE23944@dhcp22.suse.cz> <20200313020851.GD68817@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200313020851.GD68817@google.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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) nothing really prevents the MADV_PAGEOUT to be called faster than the reference bit being readded. > > underestimated the issue because I was not aware of runtimes mentioned > > in the referenced links. Essentially a lot of CoW memory shared over > > security domains. > > I tend to agree about security part in the description, but still don't > agree with performance concern in the description so I'd like to remove > it in the description. Current situation is caused by security concern > unfortunately, not performance reason. Well, I have to admit that I haven't seen any actual numbers here but considering zygote like workload I would rather not even risk it. Even if the risk is theoretical I would rather put the restriction and mention it in the changelog. If somebody would like to drop this restriction it is at least more clear what to test for. -- Michal Hocko SUSE Labs