Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754640AbeALULk (ORCPT + 1 other); Fri, 12 Jan 2018 15:11:40 -0500 Received: from mail-ot0-f193.google.com ([74.125.82.193]:45297 "EHLO mail-ot0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753875AbeALULj (ORCPT ); Fri, 12 Jan 2018 15:11:39 -0500 X-Google-Smtp-Source: ACJfBotRxILO1JwPE8SQTY96IVJEzLgUSniOHOj5pR4cxFd0wally0ha5kCjSggIzHVv3uGG5moXHge9vSwlaHWZygI= MIME-Version: 1.0 In-Reply-To: <20180112172057.j33yhxb4gz6soscj@shells.gnugeneration.com> References: <20180110233252.GA14739@amd> <20180112110624.GA13254@amd> <20180112172057.j33yhxb4gz6soscj@shells.gnugeneration.com> From: Arnd Bergmann Date: Fri, 12 Jan 2018 21:11:38 +0100 X-Google-Sender-Auth: 9Fr_q5gau6U4bb79ImiXe4JcLCk Message-ID: Subject: Re: Linux 4.15-rc7 To: vcaputo@pengaru.com Cc: Pavel Machek , Olivier Galibert , Linus Torvalds , Linux Kernel Mailing List , jikos@suse.cz Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Fri, Jan 12, 2018 at 6:20 PM, wrote: > On Fri, Jan 12, 2018 at 02:23:20PM +0100, Arnd Bergmann wrote: >> Could you be more specific which 32-bit x86 chips you have that are >> affected by Meltdown? Do you mean pre-2004 Pentiums or Core-Duo >> laptops? I would guess that Cyrix/Natsemi/AMD 6x86/MediaGX/Geode >> and AMD NexGen K6/K7 also affected by Spectre but probably not >> Meltdown, and most other 32-bit microarchitectures seem to be purely >> in-order. >> > > I have some Celeron D, 4GiB dedicated servers with a 32-bit stack. > They've proven to be very reliable boxes, and are the most affordable > baremetal x86 machines I've found. I'd appreciate a PTI implementation > on them. That's an interesting setup for a number of reasons: - Celeron D are mostly 64-bit CPUs, but it depends on the particular model/stepping, so if you have a couple of them, you might be able to avoid the meltdown bug by running a 64-bit kernel with KPTI at least on some of them, or trivially replace the CPU on others. This usually works without changing user space, and tends to result in a faster system than running a 32-bit kernel as you avoid highmem. - I haven't found a definite answer on whether Netburst-based CPUs are affected by meltdown at all. Some people claim it's affected, others say it's not. If the code from https://github.com/IAIK/meltdown is successful on your Celeron D, then we know it's affected, if not, then you could decide to not care about KPTI (Spectre would still be an issue). - A 32-bit system running with mostly highmem (only the low 768 MB out of 4GB are directly mapped) means some of the exploits are harder to do in practice, as most of the page cache is not visible in the kernel, and reading data from other processes will fail more often that succeed. - Economically, it seems barely worth running these if you pay for the electricity: the CPU costs a few dollars/euros, it only takes a couple of weeks of continuous operation to exceed that in operating cost. Replacing the mainboard with a modern low end all-in-one board at 10W might pay off within a year. If you don't pay for electricity, that obviously doesn't work. Arnd