From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754218Ab2CVH3K (ORCPT ); Thu, 22 Mar 2012 03:29:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46397 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751140Ab2CVH3H (ORCPT ); Thu, 22 Mar 2012 03:29:07 -0400 Date: Thu, 22 Mar 2012 09:28:55 +0200 From: Gleb Natapov To: Anthony Liguori Cc: Avi Kivity , minyard@acm.org, Jan Kiszka , qemu-devel , "linux-kernel@vger.kernel.org" , kvm list , Corey Minyard , KAMEZAWA Hiroyuki Subject: Re: [Qemu-devel] [PATCH 0/2 v3] kvm: notify host when guest panicked Message-ID: <20120322072855.GX22368@redhat.com> References: <4F58664D.1070800@cn.fujitsu.com> <4F66E14F.3040809@cn.fujitsu.com> <4F6854F4.3060703@cn.fujitsu.com> <20120320154517.GG27928@redhat.com> <4F692723.8050904@cn.fujitsu.com> <20120321091127.GO22368@redhat.com> <4F69FF48.3010200@acm.org> <4F6A00EC.3060706@redhat.com> <4F6A29C6.2070708@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F6A29C6.2070708@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 21, 2012 at 02:19:34PM -0500, Anthony Liguori wrote: > On 03/21/2012 11:25 AM, Avi Kivity wrote: > >On 03/21/2012 06:18 PM, Corey Minyard wrote: > >> > >>>Look at drivers/char/ipmi/ipmi_msghandler.c. It has code to send panic > >>>event over IMPI. The code is pretty complex. Of course if we a going to > >>>implement something more complex than simple hypercall for panic > >>>notification we better do something more interesting with it than just > >>>saying "panic happened", like sending stack traces on all cpus for > >>>instance. > >> > >>I doubt that's the best example, unfortunately. The IPMI event log > >>has limited space and it has to be send a little piece at a time since > >>each log entry is 14 bytes. It just prints the panic string, nothing > >>else. Not that it isn't useful, it has saved my butt before. > >> > >>You have lots of interesting options with paravirtualization. You > >>could, for instance, create a console driver that delivered all > >>console output efficiently through a hypercall. That would be really > >>easy. Or, as you mention, a custom way to deliver panic information. > >>Collecting information like stack traces would be harder to > >>accomplish, as I don't think there is currently a way to get it except > >>by sending it to printk. > > > >That already exists; virtio-console (or serial console emulation) can do > >the job. > > I think the use case here is pretty straight forward: if the guest > finds itself in bad place, it wants to indicate that to the host. > > We shouldn't rely on any device drivers or complex code. It should > be as close to a single instruction as possible that can run even if > interrupts are disabled. > > An out instruction fits this very well. I think a simple protocol like: > > inl PORT -> returns a magic number indicating the presence of qemucalls > inl PORT+1 -> returns a bitmap of supported features > Sigh, one more PV isa device. > outl PORT+1 -> data reg1 > outl PORT+2 -> data reg2 > outl PORT+N -> data regN > > outl PORT -> qemucall of index value with arguments 1..N And you think you can trust panicked SMP guest to not call this on multiple cpus simultaneously? > > Regards, > > Anthony Liguori > > > > >In fact the feature can be implemented 100% host side by searching for a > >panic string signature in the console logs. > > -- Gleb.