From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: DOS VM problem with QEMU-KVM and newer kernels Date: Mon, 16 Apr 2012 12:25:37 +0200 Message-ID: <4F8BF3A1.8090200@siemens.com> References: <4F871FB6.4020906@wiesinger.com> <4F8A988A.2000009@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Gerhard Wiesinger , "qemu-devel@nongnu.org" , "kvm@vger.kernel.org" , "Roedel, Joerg" , Kevin Wolf To: Avi Kivity Return-path: Received: from goliath.siemens.de ([192.35.17.28]:16707 "EHLO goliath.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752693Ab2DPKZs (ORCPT ); Mon, 16 Apr 2012 06:25:48 -0400 In-Reply-To: <4F8A988A.2000009@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 2012-04-15 11:44, Avi Kivity wrote: > The trigger is probably > >> commit f1c1da2bde712812a3e0f9a7a7ebe7a916a4b5f4 >> Author: Jan Kiszka >> Date: Tue Oct 18 18:23:11 2011 +0200 >> >> KVM: SVM: Keep intercepting task switching with NPT enabled >> >> AMD processors apparently have a bug in the hardware task switching >> support when NPT is enabled. If the task switch triggers a NPF, we can >> get wrong EXITINTINFO along with that fault. On resume, spurious >> exceptions may then be injected into the guest. >> >> We were able to reproduce this bug when our guest triggered #SS >> and the >> handler were supposed to run over a separate task with not yet touched >> stack pages. >> >> Work around the issue by continuing to emulate task switches even in >> NPT mode. >> >> Signed-off-by: Jan Kiszka >> Signed-off-by: Marcelo Tosatti > > Although it's not the patch's direct fault - it simply exposed an > existing bug in kvm. > > Things to try: > - revert the patch with a newer kernel > - try 3.4-rc2 which has some task switch fixes from Kevin; if you want a > Fedora kernel, use rawhide's [2] > - post traces [1] > > Jan, Joerg, was an AMD erratum published for the bug? It wasn't an erratum but a documented feature limitation in the AMD architecture that was simply ignored by the old code. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux