Re: [Qemu-devel] [PATCH] kvm: ioapic: conditionally delay irq delivery duringeoi broadcast

["Zhang Haoyu" <zhanghy@sangfor.com>]

>> Currently, we call ioapic_service() immediately when we find the irq is still
>> active during eoi broadcast. But for real hardware, there's some dealy between
>> the EOI writing and irq delivery (system bus latency?). So we need to emulate
>> this behavior. Otherwise, for a guest who haven't register a proper irq handler
>> , it would stay in the interrupt routine as this irq would be re-injected
>> immediately after guest enables interrupt. This would lead guest can't move
>> forward and may miss the possibility to get proper irq handler registered (one
>> example is windows guest resuming from hibernation).
>> 
>> As there's no way to differ the unhandled irq from new raised ones, this patch
>> solve this problems by scheduling a delayed work when the count of irq injected
>> during eoi broadcast exceeds a threshold value. After this patch, the guest can
>> move a little forward when there's no suitable irq handler in case it may
>> register one very soon and for guest who has a bad irq detection routine ( such
>> as note_interrupt() in linux ), this bad irq would be recognized soon as in the
>> past.
>> 
>> Cc: Michael S. Tsirkin <mst@redhat.com>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> Signed-off-by: Zhang Haoyu <zhanghy@sangfor.com>
>> ---
>>  include/trace/events/kvm.h | 20 ++++++++++++++++++
>>  virt/kvm/ioapic.c          | 51 ++++++++++++++++++++++++++++++++++++++++++++--
>>  virt/kvm/ioapic.h          |  6 ++++++
>>  3 files changed, 75 insertions(+), 2 deletions(-)
>> 
>> diff --git a/include/trace/events/kvm.h b/include/trace/events/kvm.h
>> index 908925a..b05f688 100644
>> --- a/include/trace/events/kvm.h
>> +++ b/include/trace/events/kvm.h
>> @@ -95,6 +95,26 @@ TRACE_EVENT(kvm_ioapic_set_irq,
>>  		  __entry->coalesced ? " (coalesced)" : "")
>>  );
>>  
>> +TRACE_EVENT(kvm_ioapic_delayed_eoi_inj,
>> +	    TP_PROTO(__u64 e),
>> +	    TP_ARGS(e),
>> +
>> +	TP_STRUCT__entry(
>> +		__field(	__u64,		e		)
>> +	),
>> +
>> +	TP_fast_assign(
>> +		__entry->e		= e;
>> +	),
>> +
>> +	TP_printk("dst %x vec=%u (%s|%s|%s%s)",
>> +		  (u8)(__entry->e >> 56), (u8)__entry->e,
>> +		  __print_symbolic((__entry->e >> 8 & 0x7), kvm_deliver_mode),
>> +		  (__entry->e & (1<<11)) ? "logical" : "physical",
>> +		  (__entry->e & (1<<15)) ? "level" : "edge",
>> +		  (__entry->e & (1<<16)) ? "|masked" : "")
>> +);
>> +
>>  TRACE_EVENT(kvm_msi_set_irq,
>>  	    TP_PROTO(__u64 address, __u64 data),
>>  	    TP_ARGS(address, data),
>> diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
>> index e8ce34c..a36c4c4 100644
>> --- a/virt/kvm/ioapic.c
>> +++ b/virt/kvm/ioapic.c
>> @@ -405,6 +405,24 @@ void kvm_ioapic_clear_all(struct kvm_ioapic *ioapic, int irq_source_id)
>>  	spin_unlock(&ioapic->lock);
>>  }
>>  
>> +static void kvm_ioapic_eoi_inject_work(struct work_struct *work)
>> +{
>> +	int i;
>> +	struct kvm_ioapic *ioapic = container_of(work, struct kvm_ioapic,
>> +						 eoi_inject.work);
>> +	spin_lock(&ioapic->lock);
>> +	for (i = 0; i < IOAPIC_NUM_PINS; i++) {
>> +		union kvm_ioapic_redirect_entry *ent = &ioapic->redirtbl[i];
>> +
>> +		if (ent->fields.trig_mode != IOAPIC_LEVEL_TRIG)
>> +			continue;
>> +
>> +		if (ioapic->irr & (1 << i) && !ent->fields.remote_irr)
>> +			ioapic_service(ioapic, i, false);
>> +	}
>> +	spin_unlock(&ioapic->lock);
>> +}
>> +
>>  static void __kvm_ioapic_update_eoi(struct kvm_vcpu *vcpu,
>>  			struct kvm_ioapic *ioapic, int vector, int trigger_mode)
>>  {
>> @@ -435,8 +453,33 @@ static void __kvm_ioapic_update_eoi(struct kvm_vcpu *vcpu,
>>  
>>  		ASSERT(ent->fields.trig_mode == IOAPIC_LEVEL_TRIG);
>>  		ent->fields.remote_irr = 0;
>> -		if (ioapic->irr & (1 << i))
>> -			ioapic_service(ioapic, i, false);
>> +		if (!ent->fields.mask && (ioapic->irr & (1 << i))) {
>
>The mask check is new - why now? You don't check it in the work handler
>as well.
>
The mask check is to avoid incrementing ioapic->irq_eoi[i] when this irq is masked, the count should be zeroed,
but needless to check it in the work handler, the check will be performed in ioapic_service().

>> +			++ioapic->irq_eoi[i];
>> +			if (ioapic->irq_eoi[i] == IOAPIC_SUCCESSIVE_IRQ_MAX_COUNT) {
>> +				/*
>> +				 * Real hardware does not deliver the irq so
>> +				 * immediately during eoi broadcast, so we need
>> +				 * to emulate this behavior. Otherwise, for
>> +				 * guests who has not registered handler of a
>> +				 * level irq, this irq would be injected
>> +				 * immediately after guest enables interrupt
>> +				 * (which happens usually at the end of the
>> +				 * common interrupt routine). This would lead
>> +				 * guest can't move forward and may miss the
>> +				 * possibility to get proper irq handler
>> +				 * registered. So we need to give some breath to
>> +				 * guest. TODO: 1 is too long?
>
>TODO should be clarify. Maybe also translate the "1" into something
>HZ-derived.
>
I will delete the TODO comment, now the risk of "1 is too long" can be ignored, 
because "if (ioapic->irq_eoi[i] == IOAPIC_SUCCESSIVE_IRQ_MAX_COUNT)" cannot be true except interrupt storm happened from the the angle of probability.

>> +				 */
>> +				schedule_delayed_work(&ioapic->eoi_inject, 1);
>> +				ioapic->irq_eoi[i] = 0;
>> +				trace_kvm_ioapic_delayed_eoi_inj(ent->bits);
>> +			}
>> +			else {
>
>I think it's the desired kernel style to do "} else {" here, but I'm not
>totally sure if that rule exists.
>
I read CodingStyle, you are right.
>> +				ioapic_service(ioapic, i, false);
>> +			}
>> +		else {
>
>I strongly suspect this version of the patch wasn't built... ;)
>
I backported it on my host linux-3.10, and built it okay.
And this time I build it on upstream, failed,
no matched "}" for if (ioapic->irq_eoi[i] == IOAPIC_SUCCESSIVE_IRQ_MAX_COUNT).
So sorry for my careless.
I will post a new patch.

>> +			ioapic->irq_eoi[i] = 0;
>> +		}
>>  	}
>>  }
>>  
>> @@ -565,12 +608,14 @@ static void kvm_ioapic_reset(struct kvm_ioapic *ioapic)
>>  {
>>  	int i;
>>  
>> +	cancel_delayed_work_sync(&ioapic->eoi_inject);
>>  	for (i = 0; i < IOAPIC_NUM_PINS; i++)
>>  		ioapic->redirtbl[i].fields.mask = 1;
>>  	ioapic->base_address = IOAPIC_DEFAULT_BASE_ADDRESS;
>>  	ioapic->ioregsel = 0;
>>  	ioapic->irr = 0;
>>  	ioapic->id = 0;
>> +	memset(ioapic->irq_eoi, 0x00, IOAPIC_NUM_PINS);
>>  	rtc_irq_eoi_tracking_reset(ioapic);
>>  	update_handled_vectors(ioapic);
>>  }
>> @@ -589,6 +634,7 @@ int kvm_ioapic_init(struct kvm *kvm)
>>  	if (!ioapic)
>>  		return -ENOMEM;
>>  	spin_lock_init(&ioapic->lock);
>> +	INIT_DELAYED_WORK(&ioapic->eoi_inject, kvm_ioapic_eoi_inject_work);
>>  	kvm->arch.vioapic = ioapic;
>>  	kvm_ioapic_reset(ioapic);
>>  	kvm_iodevice_init(&ioapic->dev, &ioapic_mmio_ops);
>> @@ -609,6 +655,7 @@ void kvm_ioapic_destroy(struct kvm *kvm)
>>  {
>>  	struct kvm_ioapic *ioapic = kvm->arch.vioapic;
>>  
>> +	cancel_delayed_work_sync(&ioapic->eoi_inject);
>>  	if (ioapic) {
>>  		kvm_io_bus_unregister_dev(kvm, KVM_MMIO_BUS, &ioapic->dev);
>>  		kvm->arch.vioapic = NULL;
>> diff --git a/virt/kvm/ioapic.h b/virt/kvm/ioapic.h
>> index 90d43e9..260ac0a 100644
>> --- a/virt/kvm/ioapic.h
>> +++ b/virt/kvm/ioapic.h
>> @@ -34,6 +34,10 @@ struct kvm_vcpu;
>>  #define	IOAPIC_INIT			0x5
>>  #define	IOAPIC_EXTINT			0x7
>>  
>> +/* max successive count of the same irq during ioapic eoi broadcast, if this limitation reached,
>> +   which can be considered as interrupt storm happened */
>> +#define IOAPIC_SUCCESSIVE_IRQ_MAX_COUNT 10000
>> +
>>  #ifdef CONFIG_X86
>>  #define RTC_GSI 8
>>  #else
>> @@ -59,6 +63,8 @@ struct kvm_ioapic {
>>  	spinlock_t lock;
>>  	DECLARE_BITMAP(handled_vectors, 256);
>>  	struct rtc_status rtc_status;
>> +	struct delayed_work eoi_inject;
>> +	u32 irq_eoi[IOAPIC_NUM_PINS];
>>  };
>>  
>>  #ifdef DEBUG
>> 
>
>The general approach looks sane to me. I was first concerned the delay
>could affect non-broken guests as well, but the loop counter prevents
>this effectively.
>

>Jan