linux-kernel - Re: [v3 25/26] KVM: Suppress posted-interrupt when 'SN' is set

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Date:	Thu, 18 Dec 2014 09:38:06 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [v3 25/26] KVM: Suppress posted-interrupt when 'SN' is set



On 18/12/2014 04:14, Wu, Feng wrote:
> 
> 
>> -----Original Message-----
>> From: linux-kernel-owner@...r.kernel.org
>> [mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of Paolo Bonzini
>> Sent: Thursday, December 18, 2014 1:43 AM
>> To: Wu, Feng; Thomas Gleixner; Ingo Molnar; H. Peter Anvin; x86@...nel.org;
>> Gleb Natapov; Paolo Bonzini; dwmw2@...radead.org; joro-zLv9SwRftAIdnm+yROfE0A@...lic.gmane.org; Alex
>> Williamson; Jiang Liu
>> Cc: iommu@...ts.linux-foundation.org; linux-kernel-u79uwXL29TY76Z2rM5mHXA@...lic.gmane.org; KVM list;
>> Eric Auger
>> Subject: Re: [v3 25/26] KVM: Suppress posted-interrupt when 'SN' is set
>>
>>
>>
>> On 12/12/2014 16:14, Feng Wu wrote:
>>> Currently, we don't support urgent interrupt, all interrupts
>>> are recognized as non-urgent interrupt, so we cannot send
>>> posted-interrupt when 'SN' is set.
>>
>> Can this happen?  If the vcpu is in guest mode, it cannot have been
>> scheduled out, and that's the only case when SN is set.
>>
>> Paolo
> 
> Currently, the only place where SN is set is vCPU is preempted and waiting for
> the next scheduling in the runqueue. But I am not sure whether we need to
> set SN for other purpose in future. Adding SN checking here is just to follow
> the Spec. non-urgent interrupts are suppressed when SN is set.

I would change that to a WARN_ON_ONCE then.

Paolo

> Thanks,
> Feng
> 
>>
>>> Signed-off-by: Feng Wu
>> <feng.wu-ral2JQCrhuEAvxtiuMwx3w@...lic.gmane.org>
>>> ---
>>>  arch/x86/kvm/vmx.c | 11 +++++++++--
>>>  1 file changed, 9 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>> index a1c83a2..0aee151 100644
>>> --- a/arch/x86/kvm/vmx.c
>>> +++ b/arch/x86/kvm/vmx.c
>>> @@ -4401,15 +4401,22 @@ static int vmx_vm_has_apicv(struct kvm *kvm)
>>>  static void vmx_deliver_posted_interrupt(struct kvm_vcpu *vcpu, int
>> vector)
>>>  {
>>>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>>> -	int r;
>>> +	int r, sn;
>>>
>>>  	if (pi_test_and_set_pir(vector, &vmx->pi_desc))
>>>  		return;
>>>
>>> +	/*
>>> +	 * Currently, we don't support urgent interrupt, all interrupts
>>> +	 * are recognized as non-urgent interrupt, so we cannot send
>>> +	 * posted-interrupt when 'SN' is set.
>>> +	 */
>>> +	sn = pi_test_sn(&vmx->pi_desc);
>>> +
>>>  	r = pi_test_and_set_on(&vmx->pi_desc);
>>>  	kvm_make_request(KVM_REQ_EVENT, vcpu);
>>>  #ifdef CONFIG_SMP
>>> -	if (!r && (vcpu->mode == IN_GUEST_MODE))
>>> +	if (!r && !sn && (vcpu->mode == IN_GUEST_MODE))
>>>  		apic->send_IPI_mask(get_cpu_mask(vcpu->cpu),
>>>  				POSTED_INTR_VECTOR);
>>>  	else
>>> --
>> --
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