On Thu, Mar 22, 2012 at 09:05:12AM +0800, Wen Congyang wrote: > 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. > No device should examine register value. Ideally QEMU would read registers only during migration. > 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@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > Please read the FAQ at http://www.tux.org/lkml/ > > -- 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
