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=-7.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 439D7C433E6 for ; Tue, 12 Jan 2021 22:47:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E2EA123138 for ; Tue, 12 Jan 2021 22:47:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2438480AbhALWrF (ORCPT ); Tue, 12 Jan 2021 17:47:05 -0500 Received: from mail.kernel.org ([198.145.29.99]:33980 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2436769AbhALWrE (ORCPT ); Tue, 12 Jan 2021 17:47:04 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id A3B4A230F9; Tue, 12 Jan 2021 22:46:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1610491583; bh=Rqin12tOcaSlTV0JXx5zAMTAIc0/hFy8RZqaB/MNwdY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Cg8lDoFec4nxn4ii7SgesxmcAdK/ZNLOi6F8E53v1gyb6dhcaSQ3/EepChN1EE7ri PdHcEkZ4wmBKZVHZXlAR0Axg/WiQVXdc9BAgfZlNjb4rGDaiu4kRyocGIMv/T7wBMR MxflRnIiu+vwQRcw+whzQ6OjfrlMmmT5Oa4PGt+Mx/IwfxlQzhohMkWUbRi3u6hd1q Wba5BkCe3gusMjnr7aThGGrqpYpkTjqDM+ezRikDJbRcfCFU/zxb4n4Tt7PawBBTnr bIEh4ze/hUCI1EpS+8TP0sdQx+TIiTj/9ChoepX5Fy9MB5aenX7Gf61IBY9dTCarAp eMmy7vyDn1kNA== Date: Tue, 12 Jan 2021 22:46:17 +0000 From: Will Deacon To: Nadav Amit Cc: Yu Zhao , Laurent Dufour , Peter Zijlstra , Vinayak Menon , Linus Torvalds , Andy Lutomirski , Peter Xu , Andrea Arcangeli , linux-mm , lkml , Pavel Emelyanov , Mike Kravetz , Mike Rapoport , stable , Minchan Kim , surenb@google.com Subject: Re: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect Message-ID: <20210112224616.GA10512@willie-the-truck> References: <20210105153727.GK3040@hirez.programming.kicks-ass.net> <0201238b-e716-2a3c-e9ea-d5294ff77525@linux.vnet.ibm.com> <2C7AE23B-ACA3-4D55-A907-AF781C5608F0@gmail.com> <20210112214337.GA10434@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 12, 2021 at 02:29:51PM -0800, Nadav Amit wrote: > > On Jan 12, 2021, at 1:43 PM, Will Deacon wrote: > > > > On Tue, Jan 12, 2021 at 12:38:34PM -0800, Nadav Amit wrote: > >>> On Jan 12, 2021, at 11:56 AM, Yu Zhao wrote: > >>> On Tue, Jan 12, 2021 at 11:15:43AM -0800, Nadav Amit wrote: > >>>> I will send an RFC soon for per-table deferred TLB flushes tracking. > >>>> The basic idea is to save a generation in the page-struct that tracks > >>>> when deferred PTE change took place, and track whenever a TLB flush > >>>> completed. In addition, other users - such as mprotect - would use > >>>> the tlb_gather interface. > >>>> > >>>> Unfortunately, due to limited space in page-struct this would only > >>>> be possible for 64-bit (and my implementation is only for x86-64). > >>> > >>> I don't want to discourage you but I don't think this would end up > >>> well. PPC doesn't necessarily follow one-page-struct-per-table rule, > >>> and I've run into problems with this before while trying to do > >>> something similar. > >> > >> Discourage, discourage. Better now than later. > >> > >> It will be relatively easy to extend the scheme to be per-VMA instead of > >> per-table for architectures that prefer it this way. It does require > >> TLB-generation tracking though, which Andy only implemented for x86, so I > >> will focus on x86-64 right now. > > > > Can you remind me of what we're missing on arm64 in this area, please? I'm > > happy to help get this up and running once you have something I can build > > on. > > Let me first finish making something that we can use as a basis for a > discussion. I do not waste your time before I have something ready. Sure thing! Give me a shout when you're ready. Will