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

[Marcelo Tosatti]

On Thu, Feb 26, 2015 at 08:08:15AM +0000, Wu, Feng wrote:
> 
> 
> > -----Original Message-----
> > From: Marcelo Tosatti [mailto:mtosatti@xxxxxxxxxx]
> > Sent: Thursday, February 26, 2015 5:50 AM
> > To: Wu, Feng
> > Cc: tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; hpa@xxxxxxxxx; x86@xxxxxxxxxx;
> > gleb@xxxxxxxxxx; pbonzini@xxxxxxxxxx; dwmw2@xxxxxxxxxxxxx;
> > joro@xxxxxxxxxx; alex.williamson@xxxxxxxxxx; jiang.liu@xxxxxxxxxxxxxxx;
> > eric.auger@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx
> > 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@xxxxxxxxx>
> > > ---
> > 
> > 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.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/