linux-kernel - Re: [PATCH RFC V5 3/6] kvm : Add unhalt msr to aid (live) migration

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Message-ID: <4F8D18FD.2040801@linux.vnet.ibm.com>
Date:	Tue, 17 Apr 2012 12:47:17 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>, Avi Kivity <avi@...hat.com>
CC:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	X86 <x86@...nel.org>, Jeremy Fitzhardinge <jeremy@...p.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alexander Graf <agraf@...e.de>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Gleb Natapov <gleb@...hat.com>,
	Randy Dunlap <rdunlap@...otime.net>, linux-doc@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>,
	Virtualization <virtualization@...ts.linux-foundation.org>,
	Xen <xen-devel@...ts.xensource.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [PATCH RFC V5 3/6] kvm : Add unhalt msr to aid (live) migration

On 04/12/2012 05:45 AM, Marcelo Tosatti wrote:
> On Fri, Mar 23, 2012 at 01:37:26PM +0530, Raghavendra K T wrote:
>> From: Raghavendra K T<raghavendra.kt@...ux.vnet.ibm.com>
>>

[...]
>
> Unless there is a reason to use an MSR, should use a normal ioctl
> such as KVM_{GET,SET}_MP_STATE.
>
>

I agree with you. In the current implementation, since we are not doing
any communication between host/guest (on this flag), I too felt MSR is
an overkill for this.

IMO, patch like below should do the job, which I am planning to include
in next version of patch.
Let me know if you foresee any side-effects.

---
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index aa44292..5c81a66 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5691,7 +5691,9 @@ int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu 
*vcpu,
  int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
  				    struct kvm_mp_state *mp_state)
  {
-	mp_state->mp_state = vcpu->arch.mp_state;
+	mp_state->mp_state = (vcpu->arch.mp_state == KVM_MP_STATE_HALTED &&
+				vcpu->pv_unhalted)?
+				KVM_MP_STATE_RUNNABLE : vcpu->arch.mp_state;
  	return 0;
  }

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