From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH 4/4] KVM: Rework of guest debug state writing Date: Thu, 04 Feb 2010 16:41:44 +0100 Message-ID: <4B6AEAB8.3030509@siemens.com> References: <372238c800e0d57815f472502fdf78e53463bbb6.1265232579.git.jan.kiszka@siemens.com> <20100203234929.GA11012@amt.cnet> <4B6A15EE.4050501@web.de> <20100204130038.GA15671@amt.cnet> <4B6AE1E6.9040805@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Anthony Liguori , qemu-devel@nongnu.org, Avi Kivity , kvm@vger.kernel.org To: Marcelo Tosatti Return-path: Received: from david.siemens.de ([192.35.17.14]:22448 "EHLO david.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932866Ab0BDPmJ (ORCPT ); Thu, 4 Feb 2010 10:42:09 -0500 In-Reply-To: <4B6AE1E6.9040805@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: Jan Kiszka wrote: > Marcelo Tosatti wrote: >> On Thu, Feb 04, 2010 at 01:33:50AM +0100, Jan Kiszka wrote: >>> Marcelo Tosatti wrote: >>>> On Wed, Feb 03, 2010 at 10:29:45PM +0100, Jan Kiszka wrote: >>>>> So far we synchronized any dirty VCPU state back into the kernel before >>>>> updating the guest debug state. This was a tribute to a deficit in x86 >>>>> kernels before 2.6.33. But as this is an arch-dependent issue, it is >>>>> better handle in the x86 part of KVM and remove the writeback point for >>>>> generic code. >>>> Jan, >>>> >>>> This patch breaks migration. >>> Can you elaborate what you did? I can't reproduce, and I do not see any >>> conceptual issue (given that guest debugging conflicts with migration >>> anyway). >> kvm-autotest fails (migration only, install is ok, both Linux and Win >> guests). Not sure why, perhaps the unconditional KVM_SET_GUEST_DEBUG >> corrupts state somehow? >> >> Tested with io thread enabled. > > That's this default-off thing, so... OK, confirmed, investigating. > Heisenbug: It first also popped up (in form of a frozen migration target) after removing this patch, but now it's totally unreproducible, whatever patch I apply or revert from my series. Base is current master. I tend to think there is a hidden issue of iothread vs. migration, unrelated to this patch. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1Nd3q4-0006dy-MX for qemu-devel@nongnu.org; Thu, 04 Feb 2010 10:41:52 -0500 Received: from [199.232.76.173] (port=60001 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Nd3q4-0006dp-2l for qemu-devel@nongnu.org; Thu, 04 Feb 2010 10:41:52 -0500 Received: from Debian-exim by monty-python.gnu.org with spam-scanned (Exim 4.60) (envelope-from ) id 1Nd3pz-0003uf-VM for qemu-devel@nongnu.org; Thu, 04 Feb 2010 10:41:51 -0500 Received: from david.siemens.de ([192.35.17.14]:22371) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1Nd3pz-0003u8-34 for qemu-devel@nongnu.org; Thu, 04 Feb 2010 10:41:47 -0500 Message-ID: <4B6AEAB8.3030509@siemens.com> Date: Thu, 04 Feb 2010 16:41:44 +0100 From: Jan Kiszka MIME-Version: 1.0 References: <372238c800e0d57815f472502fdf78e53463bbb6.1265232579.git.jan.kiszka@siemens.com> <20100203234929.GA11012@amt.cnet> <4B6A15EE.4050501@web.de> <20100204130038.GA15671@amt.cnet> <4B6AE1E6.9040805@siemens.com> In-Reply-To: <4B6AE1E6.9040805@siemens.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: [PATCH 4/4] KVM: Rework of guest debug state writing List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Marcelo Tosatti Cc: Anthony Liguori , qemu-devel@nongnu.org, kvm@vger.kernel.org, Avi Kivity Jan Kiszka wrote: > Marcelo Tosatti wrote: >> On Thu, Feb 04, 2010 at 01:33:50AM +0100, Jan Kiszka wrote: >>> Marcelo Tosatti wrote: >>>> On Wed, Feb 03, 2010 at 10:29:45PM +0100, Jan Kiszka wrote: >>>>> So far we synchronized any dirty VCPU state back into the kernel before >>>>> updating the guest debug state. This was a tribute to a deficit in x86 >>>>> kernels before 2.6.33. But as this is an arch-dependent issue, it is >>>>> better handle in the x86 part of KVM and remove the writeback point for >>>>> generic code. >>>> Jan, >>>> >>>> This patch breaks migration. >>> Can you elaborate what you did? I can't reproduce, and I do not see any >>> conceptual issue (given that guest debugging conflicts with migration >>> anyway). >> kvm-autotest fails (migration only, install is ok, both Linux and Win >> guests). Not sure why, perhaps the unconditional KVM_SET_GUEST_DEBUG >> corrupts state somehow? >> >> Tested with io thread enabled. > > That's this default-off thing, so... OK, confirmed, investigating. > Heisenbug: It first also popped up (in form of a frozen migration target) after removing this patch, but now it's totally unreproducible, whatever patch I apply or revert from my series. Base is current master. I tend to think there is a hidden issue of iothread vs. migration, unrelated to this patch. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux