Hi Avi,
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.
On 6/10/10 1:03 PM, Avi Kivity wrote:
"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.
OK, makes sense.
On 06/10/2010 12:52 PM, Pekka Enberg wrote:
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?
On 6/10/10 1:03 PM, Avi Kivity wrote:
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?
Well, power off, basically. Specifically, running a small test 'kernel'
that exists after it's done its work. I guess the thing I was missing
was that hlt is really for other purposes than power off. I guess it's
up to the hypervisor to emulate APM or something and stop the hypervisor
there?
Pekka
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