From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:35790) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S2gdU-0006G5-Pn for qemu-devel@nongnu.org; Wed, 29 Feb 2012 05:19:58 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1S2gd4-0002G7-Kn for qemu-devel@nongnu.org; Wed, 29 Feb 2012 05:19:52 -0500 Received: from mx1.redhat.com ([209.132.183.28]:17044) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S2gd4-0002Fo-D1 for qemu-devel@nongnu.org; Wed, 29 Feb 2012 05:19:26 -0500 Date: Wed, 29 Feb 2012 10:19:13 +0000 From: "Daniel P. Berrange" Message-ID: <20120229101913.GG5050@redhat.com> References: <4F4AF1FB.6000903@cn.fujitsu.com> <4F4CB926.6050600@redhat.com> <4F4D7F5E.5040202@cn.fujitsu.com> <4F4DF4C6.90609@redhat.com> <20120229095842.GF5050@redhat.com> <4F4DF86C.5010407@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <4F4DF86C.5010407@redhat.com> Subject: Re: [Qemu-devel] [PATCH] kvm: notify host when guest paniced Reply-To: "Daniel P. Berrange" List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: qemu-devel , KAMEZAWA Hiroyuki , kvm list , linux-kernel@vger.kernel.org On Wed, Feb 29, 2012 at 12:05:32PM +0200, Avi Kivity wrote: > On 02/29/2012 11:58 AM, Daniel P. Berrange wrote: > > > > > > How about using a virtio-serial channel for this? You can transfer any > > > amount of information (including the dump itself). > > > > When the guest OS has crashed, any dumps will be done from the host > > OS using libvirt's core dump mechanism. The guest OS isn't involved > > and is likely too dead to be of any use anyway. Likewise it is > > quite probably too dead to work a virtio-serial channel or any > > similarly complex device. We're really just after the simplest > > possible notification that the guest kernel has paniced. > > If it's alive enough to panic, it's alive enough to kexec its kdump > kernel. After that it can do anything. > > Guest-internal dumps are more useful IMO that host-initiated dumps. In > a cloud, the host-initiated dump is left on the host, outside the reach > of the guest admin, outside the guest image where all the symbols are, > and sometimes not even on the same host if a live migration occurred. > It's more useful in small setups, or if the problem is in the > hypervisor, not the guest. I don't think guest vs host dumps should be considered mutually exclusive, they both have pluses+minuses. Configuring kexec+kdump requires non-negligable guest admin configuration work before it's usable, and this work is guest OS specific, if it is possible at all. A permanent panic notifier that's built in the kernel by default requires zero guest admin config, and can allow host admin to automate collection of dumps across all their hosts/guests. The KVM hypercall notification is fairly trivially ported to any OS kernel, by comparison with a full virtio + virtio-serial impl. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|