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. > > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
