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

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Message-ID: <87y5pch9b3.fsf@linux.vnet.ibm.com>
Date:	Tue, 01 May 2012 08:55:20 +0530
From:	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Cc:	peterz@...radead.org, mingo@...e.hu, jeremy@...p.org,
	mtosatti@...hat.com, kvm@...r.kernel.org, x86@...nel.org,
	vatsa@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	avi@...hat.com, hpa@...or.com
Subject: Re: [RFC PATCH v1 1/5] KVM Guest: Add VCPU running/pre-empted state for guest

On Tue, 01 May 2012 06:33:59 +0530, Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com> wrote:
> 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@...llo.nl>
> > Signed-off-by: Nikunj A. Dadhania<nikunj@...ux.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?
>
Yes, thats correct. 

Regards
Nikunj

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