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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 98ADFC433F5 for ; Mon, 3 Sep 2018 01:48:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 58B922077C for ; Mon, 3 Sep 2018 01:48:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 58B922077C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727323AbeICGGl (ORCPT ); Mon, 3 Sep 2018 02:06:41 -0400 Received: from gate.crashing.org ([63.228.1.57]:46872 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725762AbeICGGk (ORCPT ); Mon, 3 Sep 2018 02:06:40 -0400 Received: from localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id w830thW3029336; Sun, 2 Sep 2018 19:55:44 -0500 Message-ID: Subject: Re: Access to non-RAM pages From: Benjamin Herrenschmidt To: Linus Torvalds , Jiri Kosina Cc: =?ISO-8859-1?Q?J=FCrgen_Gro=DF?= , Linux Kernel Mailing List , Michal Hocko , Naoya Horiguchi , Michael Ellerman , Will Deacon Date: Mon, 03 Sep 2018 10:55:42 +1000 In-Reply-To: References: <3009b28a-971c-920a-9184-900f1f3b2203@suse.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-1.fc28) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2018-09-03 at 10:48 +1000, Benjamin Herrenschmidt wrote: > On Sat, 2018-09-01 at 11:06 -0700, Linus Torvalds wrote: > > [ Adding a few new people the the cc. > > > > The issue is the worry about software-speculative accesses (ie > > things like CONFIG_DCACHE_WORD_ACCESS - not talking about the hw > > speculation now) accessing past RAM into possibly contiguous IO ] > > > > On Sat, Sep 1, 2018 at 10:27 AM Linus Torvalds > > wrote: > > > > > > If you have a machine with RAM that touches IO, you need to disable > > > the last page, exactly the same way we disable and marked reserved the > > > first page at zero. > > So I missed the departure of that train ... stupid question, with > CONFIG_DCACHE_WORD_ACCESS, if that can be unaligned (I assume it can), > what prevents it from crossing into a non-mapped page (not even IO) and > causing an oops ? Looking at a random user in fs/dcache.c its not a > uaccess-style read with recovery.... Or am I missing somethign obvious > here ? Also, if we cross page boundaries with those guys then we have a bigger problem no ? we could fall off a vmalloc page into the nether or into an ioremap mapping no ? Cheers, Ben.