> -----Original Message----- > From: linux-kernel-owner@xxxxxxxxxxxxxxx > [mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] On Behalf Of Paolo Bonzini > Sent: Thursday, December 18, 2014 4:37 PM > To: linux-kernel@xxxxxxxxxxxxxxx > Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; > linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx > 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.wu@xxxxxxxxx> > >> -- > >> To unsubscribe from this list: send the line "unsubscribe kvm" in > >> the body of a message to majordomo@xxxxxxxxxxxxxxx > >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- > 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/ -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
