From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: nVMX regression v3.13+, bisected Date: Wed, 26 Feb 2014 21:25:29 +0100 Message-ID: <530E4DB9.5050001@redhat.com> References: <530E43EC.7000600@canonical.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: Anthoine Bourgeois To: Stefan Bader , kvm@vger.kernel.org Return-path: Received: from mail-qc0-f173.google.com ([209.85.216.173]:45008 "EHLO mail-qc0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751107AbaBZUZd (ORCPT ); Wed, 26 Feb 2014 15:25:33 -0500 Received: by mail-qc0-f173.google.com with SMTP id x3so2178690qcv.32 for ; Wed, 26 Feb 2014 12:25:32 -0800 (PST) In-Reply-To: <530E43EC.7000600@canonical.com> Sender: kvm-owner@vger.kernel.org List-ID: Il 26/02/2014 20:43, Stefan Bader ha scritto: > Hi, > > I was looking at a bug report[1] about a regression on nested VMX that started > with kernel v3.13 (same issue still existed with v3.14-rc4). The problem shows > up when running a v3.13 kernel in L0 and then trying to launch a L2 (L1 was > either a v3.2 kernel or v3.13, so seemed to have no immediate influence). L2 is > trying to boot a iso image and hangs before the isolinux boot loader displays > anything. A preinstalled hd image fails to boot, too. > > I bisected this and ended up on the following commit which, when reverted made > the launch work again: > > Author: Anthoine Bourgeois > Date: Wed Nov 13 11:45:37 2013 +0100 > > kvm, vmx: Fix lazy FPU on nested guest > > If a nested guest does a NM fault but its CR0 doesn't contain the TS > flag (because it was already cleared by the guest with L1 aid) then we > have to activate FPU ourselves in L0 and then continue to L2. If TS flag > is set then we fallback on the previous behavior, forward the fault to > L1 if it asked for. > > Signed-off-by: Anthoine Bourgeois > Signed-off-by: Paolo Bonzini > > The condition to exit to L0 seems to be according to what the description says. > Could it be that the handling in L0 is doing something wrong? Thanks, I'll look at it tomorrow or Friday. Paolo