linux-kernel - Re: [PATCH RFC V10 16/18] kvm hypervisor : Simplify kvm_for_each_vcpu with kvm_irq_delivery_to

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Date:	Tue, 16 Jul 2013 23:49:03 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	mingo@...hat.com, jeremy@...p.org, x86@...nel.org,
	konrad.wilk@...cle.com, hpa@...or.com, pbonzini@...hat.com,
	linux-doc@...r.kernel.org, habanero@...ux.vnet.ibm.com,
	xen-devel@...ts.xensource.com, peterz@...radead.org,
	mtosatti@...hat.com, stefano.stabellini@...citrix.com,
	andi@...stfloor.org, attilio.rao@...rix.com, ouyang@...pitt.edu,
	gregkh@...e.de, agraf@...e.de, chegu_vinod@...com,
	torvalds@...ux-foundation.org, avi.kivity@...il.com,
	tglx@...utronix.de, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, stephan.diestelhorst@....com,
	riel@...hat.com, drjones@...hat.com,
	virtualization@...ts.linux-foundation.org,
	srivatsa.vaddagiri@...il.com
Subject: Re: [PATCH RFC V10 16/18] kvm hypervisor : Simplify kvm_for_each_vcpu
 with kvm_irq_delivery_to_apic

On 07/15/2013 09:16 PM, Gleb Natapov wrote:
> On Mon, Jul 15, 2013 at 09:06:13PM +0530, Raghavendra K T wrote:
>> On 07/14/2013 06:54 PM, Gleb Natapov wrote:
>>> On Mon, Jun 24, 2013 at 06:13:53PM +0530, Raghavendra K T wrote:
>>>> Simplify kvm_for_each_vcpu with kvm_irq_delivery_to_apic
>>>>
>>>> From: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
>>>>
>>>> Note that we are using APIC_DM_REMRD which has reserved usage.
>>>> In future if APIC_DM_REMRD usage is standardized, then we should
>>>> find some other way or go back to old method.
>>>>
>>>> Suggested-by: Gleb Natapov <gleb@...hat.com>
>>>> Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
>>>> ---
>>>>   arch/x86/kvm/lapic.c |    5 ++++-
>>>>   arch/x86/kvm/x86.c   |   25 ++++++-------------------
>>>>   2 files changed, 10 insertions(+), 20 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>>>> index e1adbb4..3f5f82e 100644
>>>> --- a/arch/x86/kvm/lapic.c
>>>> +++ b/arch/x86/kvm/lapic.c
>>>> @@ -706,7 +706,10 @@ out:
>>>>   		break;
>>>>
>>>>   	case APIC_DM_REMRD:
>>>> -		apic_debug("Ignoring delivery mode 3\n");
>>>> +		result = 1;
>>>> +		vcpu->arch.pv.pv_unhalted = 1;
>>>> +		kvm_make_request(KVM_REQ_EVENT, vcpu);
>>>> +		kvm_vcpu_kick(vcpu);
>>>>   		break;
>>>>
>>>>   	case APIC_DM_SMI:
>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>> index 92a9932..b963c86 100644
>>>> --- a/arch/x86/kvm/x86.c
>>>> +++ b/arch/x86/kvm/x86.c
>>>> @@ -5456,27 +5456,14 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
>>>>    */
>>>>   static void kvm_pv_kick_cpu_op(struct kvm *kvm, int apicid)
>>>>   {
>>>> -	struct kvm_vcpu *vcpu = NULL;
>>>> -	int i;
>>>> +	struct kvm_lapic_irq lapic_irq;
>>>>
>>>> -	kvm_for_each_vcpu(i, vcpu, kvm) {
>>>> -		if (!kvm_apic_present(vcpu))
>>>> -			continue;
>>>> +	lapic_irq.shorthand = 0;
>>>> +	lapic_irq.dest_mode = 0;
>>>> +	lapic_irq.dest_id = apicid;
>>>>
>>>> -		if (kvm_apic_match_dest(vcpu, 0, 0, apicid, 0))
>>>> -			break;
>>>> -	}
>>>> -	if (vcpu) {
>>>> -		/*
>>>> -		 * Setting unhalt flag here can result in spurious runnable
>>>> -		 * state when unhalt reset does not happen in vcpu_block.
>>>> -		 * But that is harmless since that should soon result in halt.
>>>> -		 */
>>>> -		vcpu->arch.pv.pv_unhalted = true;
>>>> -		/* We need everybody see unhalt before vcpu unblocks */
>>>> -		smp_wmb();
>>>> -		kvm_vcpu_kick(vcpu);
>>>> -	}
>>>> +	lapic_irq.delivery_mode = APIC_DM_REMRD;
>>> Need to make sure that delivery_mode cannot be set to APIC_DM_REMRD
>> >from MSI/IOAPIC/IPI path.
>>
>> I Gleb,
>> I need your help here since I do not know much about apic.
>>
>> so are you saying explicitly checking that, kvm_set_msi_irq,
>> apic_send_ipi, native_setup_ioapic_entry, does not have
>> APIC_DM_REMRD as delivery_mode set?
>>
> Yes, but on a second thought what bad can happen if we will not check it?
> If guest configures irq to inject APIC_DM_REMRD interrupt this may
> needlessly wakeup sleeping vcpu and it will try to accrue spinlock
> again, so no correctness problem only performance. If this is the case
> lets leave it as it for now.

Okay.

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