From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wen Congyang Subject: Re: [PATCH 0/2 v3] kvm: notify host when guest panicked Date: Thu, 22 Mar 2012 09:05:12 +0800 Message-ID: <4F6A7AC8.5080604@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> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: minyard@acm.org, Gleb Natapov , Jan Kiszka , "linux-kernel@vger.kernel.org" , qemu-devel , Avi Kivity , kvm list , Corey Minyard , KAMEZAWA Hiroyuki To: Anthony Liguori Return-path: In-Reply-To: <4F6A29C6.2070708@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org Sender: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org List-Id: kvm.vger.kernel.org At 03/22/2012 03:19 AM, 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: This solution is more simple than using virtio-serial. > > inl PORT -> returns a magic number indicating the presence of qemucalls I donot understantd this instruction's purpose. > inl PORT+1 -> returns a bitmap of supported features Hmm, we can execute this instruction when guest starts. If the userspace does not process panicked event, there is no need to notify it. > > outl PORT+1 -> data reg1 > outl PORT+2 -> data reg2 > outl PORT+N -> data regN We can get the register value from vmcs. So there is no need to tell the register value to the host. If we decide to avoid touching hypervisor, I agree with this solution. Thanks Wen Congyang > > outl PORT -> qemucall of index value with arguments 1..N > > Regards, > > Anthony Liguori > >> >> In fact the feature can be implemented 100% host side by searching for a >> panic string signature in the console logs. >> > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >