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=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 D0329C0044C for ; Wed, 31 Oct 2018 21:01:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 76CED2064C for ; Wed, 31 Oct 2018 21:01:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="r+gKVQiB" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 76CED2064C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-security-module-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726377AbeKAGAp (ORCPT ); Thu, 1 Nov 2018 02:00:45 -0400 Received: from merlin.infradead.org ([205.233.59.134]:44108 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726127AbeKAGAp (ORCPT ); Thu, 1 Nov 2018 02:00:45 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=n9e9jx5bhT7iQOS4/AYUEiXPtLoQRDuZXOe6A2RZAow=; b=r+gKVQiBGZuRlTYYn0pqnPPZx w/uYbpzWqFEmKqO1lW1UDk4pwqHcTlkYOwrTom7IgA8qgZBKle+fe34Wlq6PlSguoF9RDPmq7zeRS 8Ab4CTH7M/LBH2kZCZb2FT0iD7vmeqIhwnK9v3r9k8pEwcE7nGf56wYCEMVkVN/GgHagIJZMV+ocE FaARVd5/5jIlTD5iqJZ3wU6G2Dn2JAMdS3Sbtdilc8hJwQd5FhqHsSW01ci5V1bi8WgGn+XvGtEMg 9uKedkCdXFCuT/Qlu6D7ErBAUWZj/tb8/ZslR3FSo6LnS9l4bLJZINJTVte/Su89aqSRcCZTHSZSx rY9hJ/9TA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gHxbO-0006zU-6J; Wed, 31 Oct 2018 21:00:34 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 3FE712029F887; Wed, 31 Oct 2018 22:00:32 +0100 (CET) Date: Wed, 31 Oct 2018 22:00:32 +0100 From: Peter Zijlstra To: Andy Lutomirski Cc: Matthew Wilcox , Igor Stoppa , Tycho Andersen , Kees Cook , Mimi Zohar , Dave Chinner , James Morris , Michal Hocko , Kernel Hardening , linux-integrity , LSM List , Igor Stoppa , Dave Hansen , Jonathan Corbet , Laura Abbott , Randy Dunlap , Mike Rapoport , "open list:DOCUMENTATION" , LKML , Thomas Gleixner Subject: Re: [PATCH 10/17] prmem: documentation Message-ID: <20181031210032.GA3159@hirez.programming.kicks-ass.net> References: <0A7AFB50-9ADE-4E12-B541-EC7839223B65@amacapital.net> <20181030175814.GB10491@bombadil.infradead.org> <20181030182841.GE7343@cisco> <20181030192021.GC10491@bombadil.infradead.org> <9edbdf8b-b5fb-5a82-43b4-b639f5ec8484@gmail.com> <20181030213557.GE10491@bombadil.infradead.org> <20181031100237.GN744@hirez.programming.kicks-ass.net> <659CFC78-22BF-492B-B2E4-B8E89AA08446@amacapital.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <659CFC78-22BF-492B-B2E4-B8E89AA08446@amacapital.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Wed, Oct 31, 2018 at 01:36:48PM -0700, Andy Lutomirski wrote: > > > On Oct 31, 2018, at 3:02 AM, Peter Zijlstra wrote: > > > >> On Tue, Oct 30, 2018 at 09:41:13PM -0700, Andy Lutomirski wrote: > >> To clarify some of this thread, I think that the fact that rare_write > >> uses an mm_struct and alias mappings under the hood should be > >> completely invisible to users of the API. No one should ever be > >> handed a writable pointer to rare_write memory (except perhaps during > >> bootup or when initializing a large complex data structure that will > >> be rare_write but isn't yet, e.g. the policy db). > > > > Being able to use pointers would make it far easier to do atomics and > > other things though. > > This stuff is called *rare* write for a reason. Do we really want to > allow atomics beyond just store-release? Taking a big lock and then > writing in the right order should cover everything, no? Ah, so no. That naming is very misleading. We modify page-tables a _lot_. The point is that only a few sanctioned sites are allowed writing to it, not everybody. I _think_ the use-case for atomics is updating the reference counts of objects that are in this write-rare domain. But I'm not entirely clear on that myself either. I just really want to avoid duplicating that stuff.