* KVM_EXIT_HALT and KVM_CREATE_IRQCHIP
@ 2010-06-10 9:52 Pekka Enberg
2010-06-10 10:03 ` Avi Kivity
0 siblings, 1 reply; 4+ messages in thread
From: Pekka Enberg @ 2010-06-10 9:52 UTC (permalink / raw)
To: Avi Kivity, KVM General, Cyrill Gorcunov, Asias He
Hi!
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.
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?
Pekka
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: KVM_EXIT_HALT and KVM_CREATE_IRQCHIP
2010-06-10 9:52 KVM_EXIT_HALT and KVM_CREATE_IRQCHIP Pekka Enberg
@ 2010-06-10 10:03 ` Avi Kivity
2010-06-10 10:15 ` Pekka Enberg
0 siblings, 1 reply; 4+ messages in thread
From: Avi Kivity @ 2010-06-10 10:03 UTC (permalink / raw)
To: Pekka Enberg; +Cc: KVM General, Cyrill Gorcunov, Asias He
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
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: KVM_EXIT_HALT and KVM_CREATE_IRQCHIP
2010-06-10 10:03 ` Avi Kivity
@ 2010-06-10 10:15 ` Pekka Enberg
2010-06-10 10:54 ` Avi Kivity
0 siblings, 1 reply; 4+ messages in thread
From: Pekka Enberg @ 2010-06-10 10:15 UTC (permalink / raw)
To: Avi Kivity; +Cc: KVM General, Cyrill Gorcunov, Asias He
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
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: KVM_EXIT_HALT and KVM_CREATE_IRQCHIP
2010-06-10 10:15 ` Pekka Enberg
@ 2010-06-10 10:54 ` Avi Kivity
0 siblings, 0 replies; 4+ messages in thread
From: Avi Kivity @ 2010-06-10 10:54 UTC (permalink / raw)
To: Pekka Enberg; +Cc: KVM General, Cyrill Gorcunov, Asias He
On 06/10/2010 01:15 PM, Pekka Enberg wrote:
>
> 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?
>
HLT has nothing to do with power off. Qemu emulates ACPI power
management, you can either do that or roll your own (for example an I/O
port that calls exit(0) when the guest accesses it).
--
error compiling committee.c: too many arguments to function
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2010-06-10 10:54 UTC | newest]
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2010-06-10 9:52 KVM_EXIT_HALT and KVM_CREATE_IRQCHIP Pekka Enberg
2010-06-10 10:03 ` Avi Kivity
2010-06-10 10:15 ` Pekka Enberg
2010-06-10 10:54 ` Avi Kivity
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