Gleb Natapov wrote on 2012-11-26:
> On Mon, Nov 26, 2012 at 12:29:54PM +0000, Zhang, Yang Z wrote:
>> Gleb Natapov wrote on 2012-11-26:
>>> On Mon, Nov 26, 2012 at 03:51:04AM +0000, Zhang, Yang Z wrote:
>>>> Gleb Natapov wrote on 2012-11-25:
>>>>> On Wed, Nov 21, 2012 at 04:09:39PM +0800, Yang Zhang wrote:
>>>>>> Posted Interrupt allows vAPICV interrupts to inject into guest directly
>>>>>> without any vmexit.
>>>>>>
>>>>>> - When delivering a interrupt to guest, if target vcpu is running,
>>>>>> update Posted-interrupt requests bitmap and send a notification
>>>>>> event to the vcpu. Then the vcpu will handle this interrupt
>>>>>> automatically, without any software involvemnt.
>>>>> Looks like you allocating one irq vector per vcpu per pcpu and then
>>>>> migrate it or reallocate when vcpu move from one pcpu to another.
>>>>> This is not scalable and migrating irq migration slows things down.
>>>>> What's wrong with allocating one global vector for posted interrupt
>>>>> during vmx initialization and use it for all vcpus?
>>>>
>>>> Consider the following situation:
>>>> If vcpu A is running when notification event which belong to vcpu B is
> arrived,
>>> since the vector match the vcpu A's notification vector, then this event
>>> will be consumed by vcpu A(even it do nothing) and the interrupt cannot
>>> be handled in time. The exact same situation is possible with your code.
>>> vcpu B can be migrated from pcpu and vcpu A will take its place and will
>>> be assigned the same vector as vcpu B. But I fail to see why is this a
>> No, the on bit will be set to prevent notification event when vcpu B start
> migration. And it only free the vector before it going to run in another pcpu.
> There is a race. Sender check on bit, vcpu B migrate to another pcpu and
> starts running there, vcpu A takes vpuc's B vector, sender send PI vcpu
> A gets it.
Yes, it do exist. But I think it should be ok even this happens.
>>
>>> problem. vcpu A will ignore PI since pir will be empty and vcpu B should
>>> detect new event during next vmentry.
>> Yes, but the next vmentry may happen long time later and interrupt cannot be
> serviced until next vmentry. In current way, it will cause vmexit and re-schedule
> the vcpu B.
> Vmentry will happen when scheduler will decide that vcpu can run. There
I don't know how scheduler can know the vcpu can run in this case, can you elaborate it?
I thought it may have problems with global vector in some cases(maybe I am wrong, since I am not familiar with KVM scheduler):
If target VCPU is in idle, and this notification event is consumed by other VCPU, then how can scheduler know the vcpu is ready to run? Even there is a way for scheduler to know, then when? Isn't it too late?
If notification event arrived in hypervisor, then how the handler know which VCPU the notification event belong to?
> is no problem here. What you probably want to say is that vcpu may not be
> aware of interrupt happening since it was migrated to different vcpu
> just after PI IPI was sent and thus missed it. But than PIR interrupts
> should be processed during vmentry on another pcpu:
>
> Sender: Guest:
>
> set pir
> set on
> if (vcpu in guest mode on pcpu1)
> vmexit on pcpu1
> vmentry on pcpu2
> process pir, deliver interrupt
> send PI IPI to pcpu1
>>
>>>>
>>>>>
>>>>>> + if (!cfg) {
>>>>>> + free_irq_at(irq, NULL);
>>>>>> + return 0;
>>>>>> + }
>>>>>> +
>>>>>> + raw_spin_lock_irqsave(&vector_lock, flags);
>>>>>> + if (!__assign_irq_vector(irq, cfg, mask))
>>>>>> + ret = irq;
>>>>>> + raw_spin_unlock_irqrestore(&vector_lock, flags);
>>>>>> +
>>>>>> + if (ret) {
>>>>>> + irq_set_chip_data(irq, cfg);
>>>>>> + irq_clear_status_flags(irq, IRQ_NOREQUEST);
>>>>>> + } else {
>>>>>> + free_irq_at(irq, cfg);
>>>>>> + }
>>>>>> + return ret;
>>>>>> +}
>>>>>
>>>>> This function is mostly cut&paste of create_irq_nr().
>>>>
>>>> Yes, this function allow to allocate vector from specified cpu.
>>>>
>>> Does not justify code duplication.
>> ok. will change it in next version.
>>
> Please use single global vector in the next version.
>
>>>>>>
>>>>>> if (kvm_x86_ops->has_virtual_interrupt_delivery(vcpu))
>>>>>> apic->vid_enabled = true;
>>>>>> +
>>>>>> + if (kvm_x86_ops->has_posted_interrupt(vcpu))
>>>>>> + apic->pi_enabled = true;
>>>>>> +
>>>>> This is global state, no need per apic variable.
>> Even all vcpus use the same setting, but according to SDM, apicv really is a per
> apic variable.
> It is not per vapic in our implementation and this is what is
> important here.
>
>> Anyway, if you think we should not put it here, where is the best place?
> It is not needed, just use has_posted_interrupt(vcpu) instead.
ok
>>
>>>>>> @@ -1555,6 +1611,11 @@ static void vmx_vcpu_load(struct kvm_vcpu
>>> *vcpu,
>>>>> int cpu)
>>>>>> struct desc_ptr *gdt = &__get_cpu_var(host_gdt);
>>>>>> unsigned long sysenter_esp;
>>>>>> + if (enable_apicv_pi && to_vmx(vcpu)->pi)
>>>>>> + pi_set_on(to_vmx(vcpu)->pi);
>>>>>> +
>>>>> Why?
>>>>
>>>> Here means the vcpu start migration. So we should prevent the
>>>> notification event until migration end.
>>>>
>>> You check for IN_GUEST_MODE while sending notification. Why is this not
>> For interrupt from emulated device, it enough. But VT-d device doesn't know
> the vcpu is migrating, so set the on bit to prevent the notification event when
> target vcpu is migrating.
> Why should VT-d device care about that? It sets bits in pir and sends
> IPI. If vcpu is running it process pir immediately, if not it will do it
> during next vmentry.
We already know the vcpu is not running(it will run soon), we can set this bit to prevent the unnecessary IPI.
>>
>>> enough? Also why vmx_vcpu_load() call means that vcpu start migration?
>> I think the follow check can ensure the vcpu is in migration, am I wrong?
>> if (vmx->loaded_vmcs->cpu != cpu)
> This code checks that this vcpu ran on that pcpu last time.
Yes, migration starts more earlier than here. But I think it should be ok to set ON bit here. Do you have any better idea?
>> {
>> if (enable_apicv_pi && to_vmx(vcpu)->pi)
>> pi_set_on(to_vmx(vcpu)->pi);
>> }
>>
>>>>>> + kvm_make_request(KVM_REQ_POSTED_INTR, vcpu);
>>>>>> +
>>>>>> kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu); local_irq_disable();
>>>>>> list_add(&vmx->loaded_vmcs->loaded_vmcss_on_cpu_link, @@ -1582,6
>>>>>> +1643,8 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
>>>>>> vcpu->cpu = -1; kvm_cpu_vmxoff(); }
>>>>>> + if (enable_apicv_pi && to_vmx(vcpu)->pi)
>>>>>> + pi_set_on(to_vmx(vcpu)->pi);
>>>>> Why?
>>>>
>>>> When vcpu schedule out, no need to send notification event to it, just set
> the
>>> PIR and wakeup it is enough.
>>> Same as above. When vcpu is scheduled out it will no be in IN_GUEST_MODE
>> Right.
>>
>>> mode. Also in this case we probably should set bit directly in IRR and leave
>>> PIR alone.
>>> From the view of hypervisor, IRR and PIR are same. For each vmentry, if PI is
> enabled, the IRR equal to (IRR | PIR). So there is no difference to set IRR or PIR if
> target vcpu is not running.
> But there is a difference for KVM code. For instance
> kvm_arch_vcpu_runnable() checks for interrupts in IRR, but not PIR.
> Migration code does the same.
Right. With PI, we need check the PIR too.
>>
>>>
>>>>
>>>>>> }
>>>>>>
>>>>>> static void vmx_fpu_activate(struct kvm_vcpu *vcpu)
>>>>>> @@ -2451,12 +2514,6 @@ static __init int setup_vmcs_config(struct
>>>>> vmcs_config *vmcs_conf)
>>>>>> u32 _vmexit_control = 0;
>>>>>> u32 _vmentry_control = 0;
>>>>>> - min = PIN_BASED_EXT_INTR_MASK | PIN_BASED_NMI_EXITING;
>>>>>> - opt = PIN_BASED_VIRTUAL_NMIS;
>>>>>> - if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_PINBASED_CTLS,
>>>>>> - &_pin_based_exec_control) < 0)
>>>>>> - return -EIO;
>>>>>> -
>>>>>> min = CPU_BASED_HLT_EXITING |
>>>>>> #ifdef CONFIG_X86_64
>>>>>> CPU_BASED_CR8_LOAD_EXITING |
>>>>>> @@ -2531,6 +2588,17 @@ static __init int setup_vmcs_config(struct
>>>>> vmcs_config *vmcs_conf)
>>>>>> &_vmexit_control) < 0)
>>>>>> return -EIO;
>>>>>> + min = PIN_BASED_EXT_INTR_MASK | PIN_BASED_NMI_EXITING;
>>>>>> + opt = PIN_BASED_VIRTUAL_NMIS | PIN_BASED_POSTED_INTR;
>>>>>> + if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_PINBASED_CTLS,
>>>>>> + &_pin_based_exec_control) < 0)
>>>>>> + return -EIO;
>>>>>> +
>>>>>> + if (!(_cpu_based_2nd_exec_control &
>>>>>> + SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY) ||
>>>>>> + !(_vmexit_control & VM_EXIT_ACK_INTR_ON_EXIT))
>>>>>> + _pin_based_exec_control &= ~PIN_BASED_POSTED_INTR;
>>>>>> +
>>>>>> min = 0; opt = VM_ENTRY_LOAD_IA32_PAT; if
>>>>>> (adjust_vmx_controls(min, opt, MSR_IA32_VMX_ENTRY_CTLS, @@ -2715,6
>>>>>> +2783,9 @@ static __init int hardware_setup(void) if
>>>>>> (!cpu_has_vmx_virtual_intr_delivery()) enable_apicv_vid = 0;
>>>>>> + if (!cpu_has_vmx_posted_intr() || !x2apic_enabled())
>>>>> In nested guest x2apic may be enabled without irq remapping. Check for
>>>>> irq remapping here.
>>>>
>>>> There are no posted interrupt available in nested case. We don't need
>>>> to check IR here.
>>>>
>>> One day emulation will be added. If pre-request for PI is IR check
>>> for IR.
>>
>>
>>> BTW why IR is needed for PI. To deliver assigned devices interrupts
>>> directly into a guest sure, but why is it required for delivering
>>> interrupts from emulated devices or IPIs?
>> Posted Interrupt support is Xeon only and these platforms will have x2APIC. So,
> Linux will enable x2APIC on these platforms. So we only want to enable PI when
> x2apic is enabled and IR is required for x2apic.
> The fact that x2APIC is available on all platform that support PI is
> irrelevant. If one is not strictly required by the other by architecture
> do not couple them.
Right. We only want to simply the implementation of enable "ack intr on exit". If IR enabled, then don't need to check the trig mode(all interrupts are edge) when using self IPI to regenerate the interrupt.
>>
>>>>>
>>>>>> + enable_apicv_pi = 0;
>>>>>> +
>>>>>> if (nested) nested_vmx_setup_ctls_msrs(); @@ -3881,6 +3952,93
>>>>>> @@ static void ept_set_mmio_spte_mask(void)
>>>>>> kvm_mmu_set_mmio_spte_mask(0xffull << 49 | 0x6ull); }
>>>>>> +irqreturn_t pi_handler(int irq, void *data)
>>>>>> +{
>>>>>> + struct vcpu_vmx *vmx = data;
>>>>>> +
>>>>>> + kvm_make_request(KVM_REQ_EVENT, &vmx->vcpu);
>>>>>> + kvm_vcpu_kick(&vmx->vcpu);
>>>>>> +
>>>>>> + return IRQ_HANDLED;
>>>>>> +}
>>>>>> +
>>>>>> +static int vmx_has_posted_interrupt(struct kvm_vcpu *vcpu)
>>>>>> +{
>>>>>> + return irqchip_in_kernel(vcpu->kvm) && enable_apicv_pi;
>>>>>> +}
>>>>>> +
>>>>>> +static void vmx_pi_migrate(struct kvm_vcpu *vcpu)
>>>>>> +{
>>>>>> + int ret = 0;
>>>>>> + struct vcpu_vmx *vmx = to_vmx(vcpu);
>>>>>> +
>>>>>> + if (!enable_apicv_pi)
>>>>>> + return ;
>>>>>> +
>>>>>> + preempt_disable();
>>>>>> + local_irq_disable();
>>>>>> + if (!vmx->irq) {
>>>>>> + ret = arch_pi_alloc_irq(vmx);
>>>>>> + if (ret < 0) {
>>>>>> + vmx->irq = -1;
>>>>>> + goto out;
>>>>>> + }
>>>>>> + vmx->irq = ret;
>>>>>> +
>>>>>> + ret = request_irq(vmx->irq, pi_handler, IRQF_NO_THREAD,
>>>>>> + "Posted Interrupt", vmx);
>>>>>> + if (ret) {
>>>>>> + vmx->irq = -1;
>>>>>> + goto out;
>>>>>> + }
>>>>>> +
>>>>>> + ret = arch_pi_get_vector(vmx->irq);
>>>>>> + } else
>>>>>> + ret = arch_pi_migrate(vmx->irq, smp_processor_id());
>>>>>> +
>>>>>> + if (ret < 0) {
>>>>>> + vmx->irq = -1;
>>>>>> + goto out;
>>>>>> + } else {
>>>>>> + vmx->vector = ret;
>>>>>> + vmcs_write16(POSTED_INTR_NV, vmx->vector);
>>>>>> + pi_clear_on(vmx->pi);
>>>>>> + }
>>>>>> +out:
>>>>>> + local_irq_enable();
>>>>>> + preempt_enable();
>>>>>> + return ;
>>>>>> +}
>>>>>> +
>>>>>> +static int vmx_send_nv(struct kvm_vcpu *vcpu,
>>>>>> + int vector)
>>>>>> +{
>>>>>> + struct vcpu_vmx *vmx = to_vmx(vcpu);
>>>>>> +
>>>>>> + if (unlikely(vmx->irq == -1))
>>>>>> + return 0;
>>>>>> +
>>>>>> + if (vcpu->cpu == smp_processor_id()) {
>>>>>> + pi_set_on(vmx->pi);
>>>>> Why? You clear this bit anyway in vmx_update_irq() during guest entry.
>>>> Here means the target vcpu already in vmx non-root mode. Then it will
>>> consume the interrupt on next vm entry and we don't need to send the
>>> notification event from other cpu, just update PIR is enough.
>>> I understand why you avoid sending PI IPI here, but you do not update
>>> pir in this case either. You only set "on" bit here and set vector directly
>>> in IRR in __apic_accept_irq() since vmx_send_nv() returns 0 in this case.
>>> Interrupt is delivered from IRR on the next entry.
>> As I mentioned, IRR is basically same as PIR.
>>
> That does not explain why are you setting "on" without setting bit in pir.
Right. Just set the PIR and return 1 is enough.
>>>>
>>>>>> + return 0; + } + + pi_set_pir(vector, vmx->pi); + if
>>>>>> (!pi_test_and_set_on(vmx->pi) && (vcpu->mode == IN_GUEST_MODE)) {
>>>>>> + apic->send_IPI_mask(get_cpu_mask(vcpu->cpu), vmx->vector);
>>>>>> + return 1; + } + return 0; +} + +static void free_pi(struct
>>>>>> vcpu_vmx *vmx) +{ + if (enable_apicv_pi) { + kfree(vmx->pi);
>>>>>> + arch_pi_free_irq(vmx->irq, vmx); + } +} +
>>>>>> /*
>>>>>> * Sets up the vmcs for emulated real mode.
>>>>>> */
>>>>>> @@ -3890,6 +4048,7 @@ static int vmx_vcpu_setup(struct vcpu_vmx
> *vmx)
>>>>>> unsigned long a;
>>>>>> #endif
>>>>>> int i;
>>>>>> + u32 pin_based_exec_ctrl = vmcs_config.pin_based_exec_ctrl;
>>>>>>
>>>>>> /* I/O */ vmcs_write64(IO_BITMAP_A, __pa(vmx_io_bitmap_a)); @@
>>>>>> -3901,8 +4060,10 @@ static int vmx_vcpu_setup(struct vcpu_vmx
>>>>>> *vmx) vmcs_write64(VMCS_LINK_POINTER, -1ull); /* 22.3.1.5 */
>>>>>>
>>>>>> /* Control */
>>>>>> - vmcs_write32(PIN_BASED_VM_EXEC_CONTROL,
>>>>>> - vmcs_config.pin_based_exec_ctrl); + if (!enable_apicv_pi)
>>>>>> + pin_based_exec_ctrl &= ~PIN_BASED_POSTED_INTR; +
>>>>>> + vmcs_write32(PIN_BASED_VM_EXEC_CONTROL, pin_based_exec_ctrl);
>>>>>>
>>>>>> vmcs_write32(CPU_BASED_VM_EXEC_CONTROL,
>>>>> vmx_exec_control(vmx));
>>>>>>
>>>>>> @@ -3920,6 +4081,12 @@ static int vmx_vcpu_setup(struct vcpu_vmx
>>> *vmx)
>>>>>> vmcs_write16(GUEST_INTR_STATUS, 0);
>>>>>> }
>>>>>> + if (enable_apicv_pi) {
>>>>>> + vmx->pi = kmalloc(sizeof(struct pi_desc),
>>>>>> + GFP_KERNEL | __GFP_ZERO);
>>>>>> + vmcs_write64(POSTED_INTR_DESC_ADDR, __pa((vmx->pi)));
>>>>>> + }
>>>>>> +
>>>>>> if (ple_gap) { vmcs_write32(PLE_GAP, ple_gap);
>>>>>> vmcs_write32(PLE_WINDOW, ple_window); @@ -6161,6 +6328,11 @@
>>>>>> static void vmx_update_irq(struct kvm_vcpu *vcpu) if
>>>>>> (!enable_apicv_vid) return ;
>>>>>> + if (enable_apicv_pi) {
>>>>>> + kvm_apic_update_irr(vcpu, (unsigned int *)vmx->pi->pir);
>>>>>> + pi_clear_on(vmx->pi);
>>>>> Why do you do that? Isn't VMX process posted interrupts on vmentry if
>>>>> "on" bit is set?
>>> Can you answer this question?
>> No, vmentry do nothing for PI. Posted interrupt only happens when an
> unmasked external interrupt arrived and the target vcpu is running. Beyond that,
> cpu follow the old way.
>>
> Now that totally contradicts what you wrote above! (unless I
> misunderstood you, in which case clarify please)
>
> From the view of hypervisor, IRR and PIR are same. For each vmentry, if
> PI is enabled, the IRR equal to (IRR | PIR). So there is no difference
> to set IRR or PIR if target vcpu is not running.
> --
> Gleb.
Sorry, maybe I mislead you. VMentry have nothing to do PI.
What I mean" IRR and PIR are same" is because this patch will copy PIR to IRR before each vmentry. So I think this two should be same in some levels. But according your comments, it may wrong.
Best regards,
Yang
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