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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 140E5C76188 for ; Tue, 16 Jul 2019 03:55:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DD39B20693 for ; Tue, 16 Jul 2019 03:55:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731221AbfGPDzW (ORCPT ); Mon, 15 Jul 2019 23:55:22 -0400 Received: from mx2.suse.de ([195.135.220.15]:49506 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730275AbfGPDzW (ORCPT ); Mon, 15 Jul 2019 23:55:22 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 3C1C7AB9D; Tue, 16 Jul 2019 03:55:21 +0000 (UTC) Subject: Re: [Xen-devel] [PATCH 0/2] Remove 32-bit Xen PV guest support To: Andrew Cooper , Andy Lutomirski , Andi Kleen Cc: Borislav Petkov , Stefano Stabellini , X86 ML , Thomas Gleixner , LinuxVirtualization , xen-devel , Boris Ostrovsky , Ingo Molnar , LKML , Alok Kataria , "H. Peter Anvin" References: <20190715113739.17694-1-jgross@suse.com> <87y30zfe9z.fsf@linux.intel.com> From: Juergen Gross Message-ID: Date: Tue, 16 Jul 2019 05:55:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: de-DE Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15.07.19 19:39, Andrew Cooper wrote: > On 15/07/2019 18:28, Andy Lutomirski wrote: >> On Mon, Jul 15, 2019 at 9:34 AM Andi Kleen wrote: >>> Juergen Gross writes: >>> >>>> The long term plan has been to replace Xen PV guests by PVH. The first >>>> victim of that plan are now 32-bit PV guests, as those are used only >>>> rather seldom these days. Xen on x86 requires 64-bit support and with >>>> Grub2 now supporting PVH officially since version 2.04 there is no >>>> need to keep 32-bit PV guest support alive in the Linux kernel. >>>> Additionally Meltdown mitigation is not available in the kernel running >>>> as 32-bit PV guest, so dropping this mode makes sense from security >>>> point of view, too. >>> Normally we have a deprecation period for feature removals like this. >>> You would make the kernel print a warning for some releases, and when >>> no user complains you can then remove. If a user complains you can't. >>> >> As I understand it, the kernel rules do allow changes like this even >> if there's a complaint: this is a patch that removes what is >> effectively hardware support. If the maintenance cost exceeds the >> value, then removal is fair game. (Obviously we weight the value to >> preserving compatibility quite highly, but in this case, Xen dropped >> 32-bit hardware support a long time ago. If the Xen hypervisor says >> that 32-bit PV guest support is deprecated, it's deprecated.) >> >> That being said, a warning might not be a bad idea. What's the >> current status of this in upstream Xen? > > So personally, I'd prefer to see support stay, but at the end of the day > it is Juergen's choice as the maintainer of the code. Especially on the security front we are unsafe with 32-bit PV Linux. And making it safe will make it so slow that the needed effort is not spent very well. Juergen