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=-5.0 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 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 E9D66C4363D for ; Fri, 25 Sep 2020 09:52:01 +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 5EDD4208A9 for ; Fri, 25 Sep 2020 09:52:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="xx+48rJX" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5EDD4208A9 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-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=iRJhMAuXcyAfUiZ40x4RqJqteVU8ntlCXgnOkqGmM6E=; b=xx+48rJXuhfwALqt1RN8l95GR J6bXm85eyaGpLDXasMvvhrhA4MQx7ucPKZ4CWwXim8i/lnGwX+gQYWSRmVysKSNH1eF0eXHWe+AI7 av/2rk7zcf/dNuIixjihAaWCeJfPPer1ORqjtuUbppO9St7mFgdenpqrwO/C2f4DFTPBzf9FZDRFW dHpHq+R1Sn+nqWqNhyn6FNwaMJL4KzxxcNvSKEoSGAndCi8XpsgsBMDjVzMnI2Aszq4Nqep5ugZ/t 5VtfBl3gXep0tKGsgxickaJ68JwBGrnScTvl5JAA1+Vg2Xf7xEoKGhpzAogHkAUzvEBspaI7RyAbn n7GC4hCfg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kLkN9-000105-Tk; Fri, 25 Sep 2020 09:50:35 +0000 Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kLkN6-0000zO-FY; Fri, 25 Sep 2020 09:50:32 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id D5927301A27; Fri, 25 Sep 2020 11:50:29 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BEFA320104626; Fri, 25 Sep 2020 11:50:29 +0200 (CEST) Date: Fri, 25 Sep 2020 11:50:29 +0200 From: Peter Zijlstra To: David Hildenbrand Subject: Re: [PATCH v6 5/6] mm: secretmem: use PMD-size pages to amortize direct map fragmentation Message-ID: <20200925095029.GX2628@hirez.programming.kicks-ass.net> References: <20200924132904.1391-1-rppt@kernel.org> <20200924132904.1391-6-rppt@kernel.org> <20200925074125.GQ2628@hirez.programming.kicks-ass.net> <8435eff6-7fa9-d923-45e5-d8850e4c6d73@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <8435eff6-7fa9-d923-45e5-d8850e4c6d73@redhat.com> 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 , Catalin Marinas , Dave Hansen , linux-mm@kvack.org, Will Deacon , linux-kselftest@vger.kernel.org, "H. Peter Anvin" , Christopher Lameter , Idan Yaniv , Thomas Gleixner , Elena Reshetova , linux-arch@vger.kernel.org, Tycho Andersen , linux-nvdimm@lists.01.org, Shuah Khan , x86@kernel.org, Matthew Wilcox , Mike Rapoport , Ingo Molnar , Michael Kerrisk , Arnd Bergmann , James Bottomley , Borislav Petkov , Alexander Viro , Andy Lutomirski , Paul Walmsley , "Kirill A. Shutemov" , Dan Williams , linux-arm-kernel@lists.infradead.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Palmer Dabbelt , linux-fsdevel@vger.kernel.org, Andrew Morton , Mike Rapoport 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, Sep 25, 2020 at 11:00:30AM +0200, David Hildenbrand wrote: > On 25.09.20 09:41, Peter Zijlstra wrote: > > On Thu, Sep 24, 2020 at 04:29:03PM +0300, Mike Rapoport wrote: > >> From: Mike Rapoport > >> > >> Removing a PAGE_SIZE page from the direct map every time such page is > >> allocated for a secret memory mapping will cause severe fragmentation of > >> the direct map. This fragmentation can be reduced by using PMD-size pages > >> as a pool for small pages for secret memory mappings. > >> > >> Add a gen_pool per secretmem inode and lazily populate this pool with > >> PMD-size pages. > > > > What's the actual efficacy of this? Since the pmd is per inode, all I > > need is a lot of inodes and we're in business to destroy the directmap, > > no? > > > > Afaict there's no privs needed to use this, all a process needs is to > > stay below the mlock limit, so a 'fork-bomb' that maps a single secret > > page will utterly destroy the direct map. > > > > I really don't like this, at all. > > As I expressed earlier, I would prefer allowing allocation of secretmem > only from a previously defined CMA area. This would physically locally > limit the pain. Given that this thing doesn't have a migrate hook, that seems like an eminently reasonable contraint. Because not only will it mess up the directmap, it will also destroy the ability of the page-allocator / compaction to re-form high order blocks by sprinkling holes throughout. Also, this is all very close to XPFO, yet I don't see that mentioned anywhere. Further still, it has this HAVE_SECRETMEM_UNCACHED nonsense which is completely unused. I'm not at all sure exposing UNCACHED to random userspace is a sane idea. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel