From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wen Congyang Subject: Re: [Qemu-devel] [PATCH 0/2 v3] kvm: notify host when guest panicked Date: Thu, 22 Mar 2012 15:40:51 +0800 Message-ID: <4F6AD783.1000706@cn.fujitsu.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> <20120322072855.GX22368@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Anthony Liguori , minyard@acm.org, kvm list , Jan Kiszka , "linux-kernel@vger.kernel.org" , qemu-devel , Avi Kivity , Corey Minyard , KAMEZAWA Hiroyuki To: Gleb Natapov Return-path: Received: from cn.fujitsu.com ([222.73.24.84]:6246 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752032Ab2CVIAY (ORCPT ); Thu, 22 Mar 2012 04:00:24 -0400 In-Reply-To: <20120322072855.GX22368@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: At 03/22/2012 03:28 PM, Gleb Natapov Wrote: > 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? We can register panic notifier in the guest kernel, and do it in the panic notifier callback. Thanks Wen Congyang > >> >> 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. > >