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=-5.3 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT 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 9776CC07E85 for ; Tue, 11 Dec 2018 14:35:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5C9A62054F for ; Tue, 11 Dec 2018 14:35:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5C9A62054F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com 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 S1726513AbeLKOfb (ORCPT ); Tue, 11 Dec 2018 09:35:31 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49838 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726231AbeLKOfa (ORCPT ); Tue, 11 Dec 2018 09:35:30 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 93F94C057F9A; Tue, 11 Dec 2018 14:35:29 +0000 (UTC) Received: from redhat.com (ovpn-112-59.ams2.redhat.com [10.36.112.59]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D45411001F45; Tue, 11 Dec 2018 14:35:26 +0000 (UTC) Date: Tue, 11 Dec 2018 14:35:23 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Eduardo Habkost Cc: Borislav Petkov , Paolo Bonzini , =?utf-8?B?SsO2cmcgUsO2ZGVs?= , Andre Przywara , kvm ML , lkml , Tom Lendacky , Eric Blake Subject: Re: kvm: RDTSCP on AMD Message-ID: <20181211143523.GH921@redhat.com> Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20181210181328.GA762@zn.tnic> <20181210183730.GJ4669@habkost.net> <20181210184153.GB5482@zn.tnic> <20181210190600.GK4669@habkost.net> <20181210194258.GD5482@zn.tnic> <20181210200843.GN4669@habkost.net> <20181211103839.GC921@redhat.com> <20181211115546.GQ4669@habkost.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20181211115546.GQ4669@habkost.net> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Tue, 11 Dec 2018 14:35:29 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 11, 2018 at 09:55:46AM -0200, Eduardo Habkost wrote: > On Tue, Dec 11, 2018 at 10:38:39AM +0000, Daniel P. Berrangé wrote: > > On Mon, Dec 10, 2018 at 06:08:43PM -0200, Eduardo Habkost wrote: > > > On Mon, Dec 10, 2018 at 08:42:58PM +0100, Borislav Petkov wrote: > > > > On Mon, Dec 10, 2018 at 05:06:00PM -0200, Eduardo Habkost wrote: > > > > > I mean documenting it. We already have code that will print > > > > > warnings if a feature isn't available. > > > > > > > > > > See my previous attempt to document the minimum kernel version > > > > > at . > > > > > > > > Something like this? > > > > > > > > I still have no clue how to add RDTSCP on pc-*-4.0 and newer. > > > > > > qemu.git master have no PC_COMPAT_3_1 and pc-*-4.0 machine-types > > > yet. I've sent another reply with additional pointers. > > > > > > > > > > > Thx. > > > > > > > > --- > > > > diff --git a/qemu-doc.texi b/qemu-doc.texi > > > > index f7ad1dfe4b69..913b2ef68d54 100644 > > > > --- a/qemu-doc.texi > > > > +++ b/qemu-doc.texi > > > > @@ -37,6 +37,7 @@ > > > > * QEMU System emulator for non PC targets:: > > > > * QEMU Guest Agent:: > > > > * QEMU User space emulator:: > > > > +* System requirements:: > > > > * Implementation notes:: > > > > * Deprecated features:: > > > > * Supported build platforms:: > > > > @@ -2813,6 +2814,13 @@ Act as if the host page size was 'pagesize' bytes > > > > Run the emulation in single step mode. > > > > @end table > > > > > > > > +@node System requirements > > > > +@chapter System requirements > > > > + > > > > +@section KVM kernel module > > > > + > > > > +On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator > > > > +require the host to be running Linux v4.5 or newer. > > > > > > > > > > Sounds good, but it would be nice to document what exactly makes > > > Linux 4.5+ necessary. e.g.: > > > > > > | On x86_64 hosts, it is recommended to run Linux 4.5 or newer on > > > | the host when using the KVM accelerator. > > > | > > > | The Opteron_G2, OpteronG3, Opteron_G4, and Opteron_G5 CPU > > > | models require KVM support for RDTSCP, which was added on > > > | Linux 4.5. > > > > > > I'm CCing some people who may help review English grammar and > > > style. > > > > Note that QEMU has a declared supported platform list which is used to > > set the minimum software versions required. > > > > https://qemu.weilnetz.de/doc/qemu-doc.html#Linux-OS > > > > Based on that policy, the Linux distros we aim to support have the > > following kernel versions: > > > > - Debian Jessie: 4.5 > > - Debian Stretch: 4.5 > > - RHEL-7: 3.10 > > - Ubuntu LTS (Xenial): 4.5 > > - OpenSUSE Leap 15: 4.12.14 > > > > So we can't require Linux 4.5 as a minimum version at this time. > > I'd like us to take a step back and consider what exactly > "support" means here. QEMU will still work on older kernels if > we add RDTSCP to the CPU models, but at the same time I would > like to document that our strict runnability guarantees may not > be kept if running Linux < 4.5. I've just noticed that this thread is not in fact on qemu-devel. So rather than debating the meaning of support here, lets discuss it once the patch adding rdtscp to OpteronG* CPU model is posted to qemu-devel. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|