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 6EA9CECE560 for ; Tue, 18 Sep 2018 13:00:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0694A2086E for ; Tue, 18 Sep 2018 13:00:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0694A2086E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lxorguk.ukuu.org.uk 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 S1729501AbeIRSdN (ORCPT ); Tue, 18 Sep 2018 14:33:13 -0400 Received: from www.llwyncelyn.cymru ([82.70.14.225]:59936 "EHLO fuzix.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726037AbeIRSdN (ORCPT ); Tue, 18 Sep 2018 14:33:13 -0400 Received: from alans-desktop (82-70-14-226.dsl.in-addr.zen.co.uk [82.70.14.226]) by fuzix.org (8.15.2/8.15.2) with ESMTP id w8ID0UE2020826; Tue, 18 Sep 2018 14:00:30 +0100 Date: Tue, 18 Sep 2018 14:00:30 +0100 From: Alan Cox To: Joerg Roedel Cc: Meelis Roos , Thomas Gleixner , Linux Kernel list , linux-mm@kvack.org, Andrea Arcangeli , Linus Torvalds Subject: Re: 32-bit PTI with THP = userspace corruption Message-ID: <20180918140030.248afa21@alans-desktop> In-Reply-To: <20180911121128.ikwptix6e4slvpt2@suse.de> References: <20180830205527.dmemjwxfbwvkdzk2@suse.de> <20180831070722.wnulbbmillxkw7ke@suse.de> <20180911114927.gikd3uf3otxn2ekq@suse.de> <20180911121128.ikwptix6e4slvpt2@suse.de> Organization: Intel Corporation X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 11 Sep 2018 14:12:22 +0200 Joerg Roedel wrote: > On Tue, Sep 11, 2018 at 02:58:10PM +0300, Meelis Roos wrote: > > The machines where I have PAE off are the ones that have less memory. > > PAE is off just for performance reasons, not lack of PAE. PAE should be > > present on all of my affected machines anyway and current distributions > > seem to mostly assume 686 and PAE anyway for 32-bit systems. > > Right, most distributions don't even provide a non-PAE kernel for their > users anymore. > > How big is the performance impact of using PAE over legacy paging? On what system. In the days of the original 36bit PAE Xeons it was around 10% when we measured it at Red Hat, but that was long ago and as you go newer it really ought to be vanishingly small. There are pretty much no machines that don't support PAE and are still even vaguely able to boot a modern Linux kernel. The oddity is the Pentium-M but most distros shipped a hack to use PAE on the Pentium M anyway as it seems to work fine. Alan