Re: Windows guest reboot failure

[Dor Laor <dor.laor-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

He, Qing wrote:
> Hi folks,
> 	I found that Windows guests often fail reboots in current
> kvm.git. Either the guest hangs, or it reports double fault exception
> which causes qemu aborts. This is not shown with -no-kvm-irqchip option.
>
> 	After some investigation, it seems that this is caused by lack
> of in-kernel components reset. Several windows guests will write RESET
> command to 8042, the keyboard controller. On receiving the command, qemu
> device model will call qemu_system_reset() to reset everything to the
> initial state. However, this mechanism is broken when in-kernel
> components is introduced: qemu doesn't communicate the reset request to
> kvm, so kvm uses stale device state on the next booting, which fails
> reboot.
>
> 	To resolve this, there are at least two options:
> 	1. modify qemu_system_reset(), so that qemu destroys kvm context
> and re-creates.
> 	2. introduce a new ioctl, say KVM_RESET, to kvm. On receiving
> this ioctl, the kernel calls reset handlers registered by other
> components (vcpu, lapic, pic, ioapic, pit, etc.), either against vm or
> against each vcpu.
>
> 	IMO, the first one is easier in modification and maintaining,
> but the second one is closer to qemu logics. Which do you think is more
> appropriate?
>
> Any comment?
>
> Thanks,
> Qing
>   
I'm voting for option 2. As you said its closer to qemu's device model 
approach and it's also similar to kernel components (*pi*)
save/restore methods. It also minimized qemu changes.
Dor.

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