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

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Message-ID: <A9667DDFB95DB7438FA9D7D576C3D87E0AC04938@SHSMSX104.ccr.corp.intel.com>
Date:	Thu, 18 Dec 2014 15:09:48 +0000
From:	"Zhang, Yang Z" <yang.z.zhang@...el.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
CC:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: RE: [v3 25/26] KVM: Suppress posted-interrupt when 'SN' is set

Paolo Bonzini wrote on 2014-12-18:
> 
> 
> On 18/12/2014 04:14, Wu, Feng wrote:
>> 
>> 
>> linux-kernel-owner@...r.kernel.org wrote on mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of Paolo:
>>> x86@...nel.org; Gleb Natapov; Paolo Bonzini; dwmw2@...radead.org;
>>> joro-zLv9SwRftAIdnm+yROfE0A@...lic.gmane.org; Alex Williamson;
>>> joro-zLv9SwRftAIdnm+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

If the vCPU is preempted, shouldn't the subsequent be ignored? What happens if a PI is occurs when vCPU is preempted?

>> 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.


Best regards,
Yang


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