Re: [RFC PATCH v1 1/5] KVM Guest: Add VCPU running/pre-empted state for guest

[Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>]

On 04/27/2012 09:53 PM, Nikunj A. Dadhania wrote:
> The patch adds guest code for msr between guest and hypervisor. The
> msr will export the vcpu running/pre-empted information to the guest
> from host. This will enable guest to intelligently send ipi to running
> vcpus and set flag for pre-empted vcpus. This will prevent waiting for
> vcpus that are not running.
>
> Suggested-by: Peter Zijlstra<a.p.zijlstra@chello.nl>
> Signed-off-by: Nikunj A. Dadhania<nikunj@linux.vnet.ibm.com>
> ---
>   arch/x86/include/asm/kvm_para.h |   10 ++++++++++
>   arch/x86/kernel/kvm.c           |   33 +++++++++++++++++++++++++++++++++
>   2 files changed, 43 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index 77266d3..f57b5cc 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -24,6 +24,7 @@
>   #define KVM_FEATURE_ASYNC_PF		4
>   #define KVM_FEATURE_STEAL_TIME		5
>   #define KVM_FEATURE_PV_UNHALT		6
> +#define KVM_FEATURE_VCPU_STATE          7

I think you intended to use KVM_FEATURE_VCPU_STATE to address
guest/host compatibility issue so that host/guest does not break
when one of them run older kernel?