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 3260EC4363D for ; Fri, 25 Sep 2020 07:43:00 +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 AF38923600 for ; Fri, 25 Sep 2020 07:42:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="ENXA5FEM" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AF38923600 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=65bJ+hGyCVNqzLS84+9cPzKKHQ6xNZ0Z8NnOBNUXvjE=; b=ENXA5FEMNSMbniNrUjCP7blmm y5fiQbaYCT/JrSy6l7pu20xuPWMuBbt54S0pvKoVDj8hwB8Ys+4WU+PvMva7xqwgsclVvXC6XID1w JIEIqzTEjLWbWAmN/YdVrhgmcCSVSqlRCxqi9J8+nKRHETy0YqiEQAn/Oi+/oMWmW9BEIQ0r5eBPP TFgumHkXAR+kAcupcV/YYKxyMQZUmW2WdZIlYXCtxVh7JEFobcnan5LgfWOBFntberj1ncgMjheSF NS38u/m9oEQRmp/J1XsQnvDIPf4HsI626Gyr3eY2Tu5KmH7JJlFFKK4UiarYSxmECNbSy75kSNsJX QSvCEdaFA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kLiMN-0003fn-97; Fri, 25 Sep 2020 07:41:39 +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 1kLiMF-0003cu-I3; Fri, 25 Sep 2020 07:41:31 +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 59EEE302753; Fri, 25 Sep 2020 09:41:25 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B942B20104626; Fri, 25 Sep 2020 09:41:25 +0200 (CEST) Date: Fri, 25 Sep 2020 09:41:25 +0200 From: Peter Zijlstra To: Mike Rapoport Subject: Re: [PATCH v6 5/6] mm: secretmem: use PMD-size pages to amortize direct map fragmentation Message-ID: <20200925074125.GQ2628@hirez.programming.kicks-ass.net> References: <20200924132904.1391-1-rppt@kernel.org> <20200924132904.1391-6-rppt@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200924132904.1391-6-rppt@kernel.org> 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 , David Hildenbrand , 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 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 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. IIRC Kirill looked at merging the directmap. I think he ran into performance issues there, but we really need something like that before something like this lands. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel