On Thu, Mar 22, 2012 at 03:44:45PM +0800, Wen Congyang wrote: > At 03/22/2012 03:31 PM, Gleb Natapov Wrote: > > 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. > > I mean: if the qemu(or other app) want to know the register value, it can > get it from vmcs. So there is no need to pass register value from guest > to host. > I understand what you mean and I am saying that reading register values shouldn't be part of the protocol. Examining cpu state postmortem is OK of course. > Another question: each outl will cause vmexit? > Yes, IIRC you can pass through io port to a guest but KVM doesn't do it. > Thanks > Wen Congyang > > > > >> 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 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
