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. -- 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
