Re: [Qemu-devel] [PATCH v11] kvm: notify host when the guest is panicked

[Wen Congyang]

At 10/31/2012 09:12 AM, Marcelo Tosatti Wrote:
> On Thu, Oct 25, 2012 at 11:42:32AM +0800, Hu Tao wrote:
>> We can know the guest is panicked when the guest runs on xen.
>> But we do not have such feature on kvm.
>>
>> Another purpose of this feature is: management app(for example:
>> libvirt) can do auto dump when the guest is panicked. If management
>> app does not do auto dump, the guest's user can do dump by hand if
>> he sees the guest is panicked.
>>
>> We have three solutions to implement this feature:
>> 1. use vmcall
>> 2. use I/O port
>> 3. use virtio-serial.
>>
>> We have decided to avoid touching hypervisor. The reason why I choose
>> choose the I/O port is:
>> 1. it is easier to implememt
>> 2. it does not depend any virtual device
>> 3. it can work when starting the kernel
> 
> It has been asked earlier why a simple virtio device is not usable
> for this (with no response IIRC).

1. We can't use virtio device when the kernel is booting.
2. The virtio's driver can be built as a module, and if it is not loaded
   and the kernel is panicked, there is no way to notify the host.
3. I/O port is more reliable than virtio device.
   If virtio's driver has some bug, and it cause kernel panicked, we can't
   use it. The I/O port is more reliable because it only depends on notifier
   chain(If we use virtio device, it also depends on notifier chain).

Thanks
Wen Congyang

> 
> Also, there is no high level documentation: purpose of the interface,
> how a management application should use it, etc.
> 
>