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=-4.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 616D1C4727F for ; Tue, 29 Sep 2020 13:07:07 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 406B8208FE for ; Tue, 29 Sep 2020 13:07:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="GqCIqM7B" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 406B8208FE 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 5BF9B6B005D; Tue, 29 Sep 2020 09:07:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 546F26B006E; Tue, 29 Sep 2020 09:07:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 40F698E0001; Tue, 29 Sep 2020 09:07:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0045.hostedemail.com [216.40.44.45]) by kanga.kvack.org (Postfix) with ESMTP id 278F46B005D for ; Tue, 29 Sep 2020 09:07:04 -0400 (EDT) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id D03EE5836 for ; Tue, 29 Sep 2020 13:07:03 +0000 (UTC) X-FDA: 77316124326.23.bee56_6012cc72718a Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin23.hostedemail.com (Postfix) with ESMTP id A77963760C for ; Tue, 29 Sep 2020 13:07:03 +0000 (UTC) X-HE-Tag: bee56_6012cc72718a X-Filterd-Recvd-Size: 4368 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf29.hostedemail.com (Postfix) with ESMTP for ; Tue, 29 Sep 2020 13:07:02 +0000 (UTC) Received: from kernel.org (unknown [87.71.73.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 579B4207F7; Tue, 29 Sep 2020 13:06:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601384821; bh=7KLc+w8RZZNLjtjf6HYJ79RwMDeyJUnvfHtVGdo8qiw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=GqCIqM7BqT+6pPkJY9utQWj93QJ3bSPfFrqfJHOudSA2n7THcsgAIPdERjDgGYpbv 3YsHM8vksG2xzKmuaMDxtRxuppf8SFckyt7f4t7JRp6EXb5ekXTVyBUz49dbfKDnNc d4WEziQvM+yY9x8NI++tf8P6f980mVqec1FHevs4= Date: Tue, 29 Sep 2020 16:06:41 +0300 From: Mike Rapoport To: David Hildenbrand Cc: Peter Zijlstra , Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , Elena Reshetova , "H. Peter Anvin" , Idan Yaniv , Ingo Molnar , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Mark Rutland , Mike Rapoport , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Thomas Gleixner , Shuah Khan , Tycho Andersen , Will Deacon , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org, x86@kernel.org Subject: Re: [PATCH v6 5/6] mm: secretmem: use PMD-size pages to amortize direct map fragmentation Message-ID: <20200929130641.GG2142832@kernel.org> 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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8435eff6-7fa9-d923-45e5-d8850e4c6d73@redhat.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 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. The prevois version contained a patch that allowed reserving a memory pool for the secretmem at boot time to avpoid splitting pages from the direct map > But my suggestion was not well received :) The disagreemet was only whether to use CMA or simple boot time reservation :-P > -- > Thanks, > > David / dhildenb > -- Sincerely yours, Mike.