linux-kernel - Re: [PATCH v3 1/4] KVM: Recover IRTE to remapped mode if the interrupt is not single-destination

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Date:	Thu, 21 Jan 2016 11:34:31 +0800
From:	Yang Zhang <yang.zhang.wz@...il.com>
To:	"Wu, Feng" <feng.wu@...el.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"rkrcmar@...hat.com" <rkrcmar@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 1/4] KVM: Recover IRTE to remapped mode if the
 interrupt is not single-destination

On 2016/1/21 11:14, Wu, Feng wrote:
>
>
>> -----Original Message-----
>> From: Yang Zhang [mailto:yang.zhang.wz@...il.com]
>> Sent: Thursday, January 21, 2016 11:06 AM
>> To: Wu, Feng <feng.wu@...el.com>; pbonzini@...hat.com;
>> rkrcmar@...hat.com
>> Cc: linux-kernel@...r.kernel.org; kvm@...r.kernel.org
>> Subject: Re: [PATCH v3 1/4] KVM: Recover IRTE to remapped mode if the
>> interrupt is not single-destination
>>
>> On 2016/1/20 9:42, Feng Wu wrote:
>>> When the interrupt is not single destination any more, we need
>>> to change back IRTE to remapped mode explicitly.
>>>
>>> Signed-off-by: Feng Wu <feng.wu@...el.com>
>>> ---
>>>    arch/x86/kvm/vmx.c | 11 ++++++++++-
>>>    1 file changed, 10 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>> index e2951b6..13d14d4 100644
>>> --- a/arch/x86/kvm/vmx.c
>>> +++ b/arch/x86/kvm/vmx.c
>>> @@ -10764,8 +10764,17 @@ static int vmx_update_pi_irte(struct kvm
>> *kvm, unsigned int host_irq,
>>>    		 */
>>>
>>>    		kvm_set_msi_irq(e, &irq);
>>> -		if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu))
>>> +		if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu)) {
>>> +			/*
>>> +			 * Make sure the IRTE is in remapped mode if
>>> +			 * we don't handle it in posted mode.
>>> +			 */
>>> +			pi_set_sn(vcpu_to_pi_desc(vcpu));
>>> +			ret = irq_set_vcpu_affinity(host_irq, NULL);
>>> +			pi_clear_sn(vcpu_to_pi_desc(vcpu));
>>> +
>>>    			continue;
>>> +		}
>>>
>>>    		vcpu_info.pi_desc_addr = __pa(vcpu_to_pi_desc(vcpu));
>>>    		vcpu_info.vector = irq.vector;
>>>
>>
>> I am still feel weird with this change: according the semantic of VT-d
>> posted interrupt, the interrupt will injected to guest through posted
>> notification and /proc/interrupts shows the same meaning. But now,
>> without being aware of user, the interrupt changes to legacy way and it
>> appears on different entry on /proc/interrupts. It looks weird.
>
> I don't think it has problem here, IMO, this is exactly how it works.
> There should be different entry for the interrupts in VT-d PI mode
> and leagcy mode.

I am not saying any problem here. Just feel weird. From a normal user's 
point, he has turned on the VT-d pi and according the semantic of VT-d 
pi, he should not observe the interrupt through legacy mode, but now he 
do see it. Maybe print out a message here will be helpful, like what you 
did for disabled lapic found during irq injection.

>
> For VT-d PI mode, it is delivered by notification event, for legacy mode,
> it is delivered by VFIO.
>
> Thanks,
> Feng
>
>>
>> Any comments? Paolo.
>>
>> --
>> best regards
>> yang


-- 
best regards
yang