> -----Original Message-----
> From: linux-kernel-ow...@vger.kernel.org
> [mailto:linux-kernel-ow...@vger.kernel.org] On Behalf Of Paolo Bonzini
> Sent: Thursday, December 18, 2014 4:37 PM
> To: linux-ker...@vger.kernel.org
> Cc: iommu@lists.linux-foundation.org; k...@vger.kernel.org;
> linux-ker...@vger.kernel.org; k...@vger.kernel.org
> Subject: Re: [v3 24/26] KVM: Update Posted-Interrupts Descriptor when vCPU
> is blocked
>
>
>
> On 18/12/2014 04:16, Wu, Feng wrote:
> >>> pre-block:
> >>> - Add the vCPU to the blocked per-CPU list
> >>> - Clear 'SN'
> >>
> >> Should SN be already clear (and NV set to POSTED_INTR_VECTOR)?
> >
> > I think the SN bit should be clear here, Adding it here is just to make sure
> > SN is clear when vCPU is blocked, so it can receive wakeup notification
> > event
> later.
>
> Then, please, WARN if the SN bit is set inside the if (vcpu->blocked).
> Inside that if you can just add the vCPU to the blocked list on vcpu_put.
>
> >> Can it
> >> happen that you go from sched-out to blocked without doing a sched-in
> first?
> >>
> >
> > I cannot imagine this scenario, can you please be more specific? Thanks a
> > lot!
>
> I cannot either. :) But it would be the case where SN is not cleared.
> So we agree that it cannot happen.
>
> >> In fact, if this is possible, what happens if vcpu->preempted &&
> >> vcpu->blocked?
> >
> > In fact, vcpu->preempted && vcpu->blocked happens sometimes, but I think
> there is
> > no issues. Please refer to the following case:
>
> I agree that there should be no issues. But if it can happen, it's better:
>
> 1) to separate the handling of preemption and blocking: preemption
> handles SN/NV/NDST, blocking handles the wakeup list.
>
Sorry, I don't quite understand this.
I think handling of preemption and blocking is separated in vmx_vcpu_put().
For vmx_vcpu_load(), the handling of SN/NV/NDST is common for preemption
and blocking.
Thanks,
Feng
> 2) to change this
>
> + } else if (vcpu->blocked) {
> + /*
> + * The vcpu is blocked on the wait queue.
> + * Store the blocked vCPU on the list of the
> + * vcpu->wakeup_cpu, which is the destination
> + * of the wake-up notification event.
>
> to just
>
> }
> if (vcpu->blocked) {
> ...
> }
> > kvm_vcpu_block()
> > -> vcpu->blocked = true;
> > -> prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
> >
> > before schedule() is called, this vcpu is woken up by another guy, so
> > the state of the vcpu associated thread is changed to TASK_RUNNING,
> > then preemption happens after interrupts or the following schedule() is
> > hit, this will call kvm_sched_out(), in which current->state ==
> TASK_RUNNING
> > and vcpu->preempted is set to true. So now vcpu->preempted and
> vcpu->blocked
> > are both true. In vmx_vcpu_put(), we will check vcpu->preempted first,
> > so
> > the vCPU will not be blocked, and the vcpu->blocked will be set the
> > false in
> > vmx_vcpu_load().
> >
> > But maybe I need do a little change to the vmx_vcpu_load() like below:
> >
> > /*
> > * Delete the vCPU from the related wakeup queue
> > * if we are resuming from blocked state
> > */
> > if (vcpu->blocked) {
> > vcpu->blocked = false;
> > + /* if wakeup_cpu == -1, the
> > vcpu is currently not
> blocked on any
> > + pCPU, don't need dequeue here
> > */
> > + if (vcpu->wakeup_cpu != -1) {
> >
> spin_lock_irqsave(&per_cpu(blocked_vcpu_on_cpu_lock,
> > vcpu->wakeup_cpu), flags);
> > list_del(&vcpu->blocked_vcpu_list);
> >
> spin_unlock_irqrestore(&per_cpu(blocked_vcpu_on_cpu_lock,
> > vcpu->wakeup_cpu), flags);
> > vcpu->wakeup_cpu = -1;
> > + }
> > }
>
> Good idea.
>
> Paolo
>
> > Any ideas about this? Thanks a lot!
> >
> > Thanks,
> > Feng
> >
> >
> > -> schedule();
> >
> >
> >>
> >>> - Set 'NV' to POSTED_INTR_WAKEUP_VECTOR
> >>>
> >>> post-block:
> >>> - Remove the vCPU from the per-CPU list
> >>
> >> Paolo
> >>
> >>> Signed-off-by: Feng Wu <feng...@intel.com>
> >> --
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