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Date: Thu, 22 Mar 2012 09:05:12 +0800 From: Wen Congyang <wency@...fujitsu.com> To: Anthony Liguori <anthony@...emonkey.ws> CC: Avi Kivity <avi@...hat.com>, minyard@....org, Gleb Natapov <gleb@...hat.com>, Jan Kiszka <jan.kiszka@...mens.com>, qemu-devel <qemu-devel@...gnu.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, kvm list <kvm@...r.kernel.org>, Corey Minyard <tcminyard@...il.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Subject: Re: [Qemu-devel] [PATCH 0/2 v3] kvm: notify host when guest panicked 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@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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