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=-2.4 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 46955C04EB8 for ; Mon, 10 Dec 2018 18:37:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 174C82081F for ; Mon, 10 Dec 2018 18:37:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 174C82081F 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 S1728313AbeLJShd (ORCPT ); Mon, 10 Dec 2018 13:37:33 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41484 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727593AbeLJShd (ORCPT ); Mon, 10 Dec 2018 13:37:33 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 15AF530014CC; Mon, 10 Dec 2018 18:37:33 +0000 (UTC) Received: from localhost (ovpn-116-63.gru2.redhat.com [10.97.116.63]) by smtp.corp.redhat.com (Postfix) with ESMTP id 48054600D7; Mon, 10 Dec 2018 18:37:32 +0000 (UTC) Date: Mon, 10 Dec 2018 16:37:30 -0200 From: Eduardo Habkost To: Borislav Petkov Cc: Paolo Bonzini , =?iso-8859-1?Q?J=F6rg_R=F6del?= , Andre Przywara , kvm ML , lkml , Tom Lendacky Subject: Re: kvm: RDTSCP on AMD Message-ID: <20181210183730.GJ4669@habkost.net> References: <20181210181328.GA762@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181210181328.GA762@zn.tnic> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Mon, 10 Dec 2018 18:37:33 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 10, 2018 at 07:13:28PM +0100, Borislav Petkov wrote: > Reviving an old thread here. > > On Wed, Jul 06, 2016 at 11:27:16PM +0200, Paolo Bonzini wrote: > > On 06/07/2016 19:34, Eduardo Habkost wrote: > > >> > Nothing is needed in the kernel actually. You can skip the intercept > > >> > by running the guest with MSR_TSC_AUX set to the guest's expected value. > > >> > Which KVM does, except that it's botched so I need to apply the > > >> > patch in https://lkml.org/lkml/2016/4/13/802. > > > Do you mean -cpu Opteron_G*,+rdtscp will be buggy on Linux v4.5? > > > (v4.5 reports rdtscp as supported in GET_SUPPORTED_CPUID) > > > > > > Can we do something to make QEMU detect the buggy kernel before > > > allowing rdtscp to be enabled, or should we just tell people to > > > upgrade their kernel? > > > > We usually just tell people to use the latest stable kernel. > > > > Adding new CPU models is not a big deal, in fact it's almost easier than > > getting compat properties right. :) > > Ok, can we finally revert > > 33b5e8c03ae7 ("target-i386: Disable rdtscp on Opteron_G* CPU models") > > in the qemu tree? > > Three years should be enough by now for > > 46896c73c1a4 ("KVM: svm: add support for RDTSCP") > > to have percolated downstream. That's Linux v4.5, released in March 2016. It isn't as simply as reverting commit 33b5e8c03ae7, but we can surely re-add RDTSCP on pc-*-4.0 and newer. I thought we added documentation mentioning the minimum kernel version required by QEMU, but I can't find it. In either case, it seems reasonable to require Linux 4.5 or newer on newer machine-types. -- Eduardo