linux-kernel - Re: [v3 24/26] KVM: Update Posted-Interrupts Descriptor when vCPU is blocked

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Date:	Thu, 26 Feb 2015 20:41:14 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	"Wu, Feng" <feng.wu@...el.com>
Cc:	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
	"gleb@...nel.org" <gleb@...nel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"joro@...tes.org" <joro@...tes.org>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"jiang.liu@...ux.intel.com" <jiang.liu@...ux.intel.com>,
	"eric.auger@...aro.org" <eric.auger@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Zhang, Yang Z" <yang.z.zhang@...el.com>
Subject: Re: [v3 24/26] KVM: Update Posted-Interrupts Descriptor when vCPU is
 blocked

On Thu, Feb 26, 2015 at 08:08:15AM +0000, Wu, Feng wrote:
> 
> 
> > -----Original Message-----
> > From: Marcelo Tosatti [mailto:mtosatti@...hat.com]
> > Sent: Thursday, February 26, 2015 5:50 AM
> > To: Wu, Feng
> > Cc: tglx@...utronix.de; mingo@...hat.com; hpa@...or.com; x86@...nel.org;
> > gleb@...nel.org; pbonzini@...hat.com; dwmw2@...radead.org;
> > joro@...tes.org; alex.williamson@...hat.com; jiang.liu@...ux.intel.com;
> > eric.auger@...aro.org; linux-kernel@...r.kernel.org;
> > iommu@...ts.linux-foundation.org; kvm@...r.kernel.org
> > Subject: Re: [v3 24/26] KVM: Update Posted-Interrupts Descriptor when vCPU
> > is blocked
> > 
> > On Fri, Dec 12, 2014 at 11:14:58PM +0800, Feng Wu wrote:
> > > This patch updates the Posted-Interrupts Descriptor when vCPU
> > > is blocked.
> > >
> > > pre-block:
> > > - Add the vCPU to the blocked per-CPU list
> > > - Clear 'SN'
> > > - Set 'NV' to POSTED_INTR_WAKEUP_VECTOR
> > >
> > > post-block:
> > > - Remove the vCPU from the per-CPU list
> > >
> > > Signed-off-by: Feng Wu <feng.wu@...el.com>
> > > ---
> > 
> > Don't see this is needed, can use the existing POSTED_INTR_VECTOR:
> > 
> > If in guest mode, IPI will be handled in VMX non-root by performed
> > PIR->IRR transfer.
> > 
> > If outside guest mode, POSTED_INTR_VECTOR IPI will be handled by host
> > which can wakeup the guest (in case it is halted).
> 
> Please see the following scenario:
> 
> 1. vCPU0 is running on pCPU0
> 2. vCPU0 is halted and vCPU1 is currently running on pCPU0
> 3. An interrupt occurs for vCPU0, if we still use POSTED_INTR_VECTOR
> for vCPU0, the notification event for vCPU0 (the event will go to pCPU1)
> will be consumed by vCPU1 incorrectly. The worst case is that vCPU0
> will never be woken up again since the wakeup event for it is always
> consumed by other vCPUs incorrectly.
> 
> Thanks,
> Feng

Ouch, yes.

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