Re: KVM_EXIT_HALT and KVM_CREATE_IRQCHIP

[Avi Kivity <avi@redhat.com>]

On 06/10/2010 12:52 PM, Pekka Enberg wrote:

>
> How is the guest supposed to halt the hypervisor if KVM_CREATE_IRQCHIP 
> is being used? The kvm_emulate_halt() function seems to handle the 
> halt event completely if irqchip_in_kernel() returns true and thus 
> never exits to the hypervisor.

"The hypervisor" is the combination of userspace and kvm.  Without 
KVM_CREATE_IRQCHIP, HLT is emulated in userspace.  With 
KVM_CREATE_IRQCHIP, HLT is emulated in the kernel.  Emulating HLT in the 
kernel results in a faster return from HLT, which occurs frequently.

If you need to break out of the kernel, send a signal to the thread 
that's running the vcpu.  That works whether the guest is running or 
sleeping.

> I see there's a KVM_GET_MP_STATE ioctl that can be used to check if 
> state is KVM_MP_STATE_HALTED but as we never exit to the hypervisor, 
> how is this supposed to work? Am I missing something obvious here?

In general you only rarely want to check the state (example are for 
debugging and for live migration).  It's not a stable value (the guest 
executing HLT, or a guest interrupt delivered, will change its value).  
What's your use case?

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