Re: [Qemu-devel] [PATCH 3/3] QEMU kvm/i386 : Adding KICK_VCPU capability support in i386 target.

[Alexander Graf]

On 19.12.2011, at 14:59, Avi Kivity wrote:

> On 12/19/2011 03:54 PM, Alexander Graf wrote:
>> On 04.12.2011, at 19:26, Raghavendra K T wrote:
>> 
>>> Extend the KVM Hypervisor to enable KICK_VCPU feature that allows
>>> a vcpu to kick the halted vcpu to continue with execution in PV ticket
>>> spinlock.
>>> 
>>> Signed-off-by: Srivatsa Vaddagiri <address@hidden>
>>> Signed-off-by: Raghavendra K T <address@hidden>
>>> ---
>>> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
>>> index 5bfc21f..69bce21 100644
>>> --- a/target-i386/kvm.c
>>> +++ b/target-i386/kvm.c
>>> @@ -97,6 +97,7 @@ struct kvm_para_features {
>>>    { KVM_CAP_NOP_IO_DELAY, KVM_FEATURE_NOP_IO_DELAY },
>>>    { KVM_CAP_PV_MMU, KVM_FEATURE_MMU_OP },
>>>    { KVM_CAP_ASYNC_PF, KVM_FEATURE_ASYNC_PF },
>>> +    { KVM_CAP_KICK_VCPU, KVM_FEATURE_KICK_VCPU },
>> 
>> So this is handled in the kernel? Who enables the feature? Is it always on? 
>> Why bother with it in user space at all then?
> 
> Backwards compatibility

If we want backwards compatibility, we need more than just a simple feature 
check, no? Oh, you feed that into CPUID? That's nifty. Ok, so you behave like 
VMX/SVM do on real hardware - you always expose the functionality but don't 
list it in CPUID for older user space.

Makes sense.


Alex