Re: Windows guest reboot failure

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@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.
>   

That's too destructive, there's lots of state to recreate, things like 
dirty page logging need to be reinitialized.

> 	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.
>
>   

There's a third option: let the regular qemu logic work, and after that 
copy the state to kvm (just like after vm restore).  I tried that but 
there were problems so I dropped it.  But the approach should work.

> 	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?
>
>   

I think #2.  Synchronization will be difficult; we'll need to send 
signals to all other vcpus so that they drop the vcpu mutex.


-- 
error compiling committee.c: too many arguments to function


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