From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: KVM: PIC: enhance IPI avoidance
Date: Wed, 24 Sep 2008 11:40:38 -0300
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Cc: kvm-devel <kvm@vger.kernel.org>
To: Avi Kivity <avi@redhat.com>
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On Wed, Sep 24, 2008 at 03:19:47PM +0300, Avi Kivity wrote:
>> Index: kvm/arch/x86/kvm/irq.h
>> ===================================================================
>> --- kvm.orig/arch/x86/kvm/irq.h
>> +++ kvm/arch/x86/kvm/irq.h
>> @@ -42,6 +42,7 @@ struct kvm_kpic_state {
>>  	u8 irr;		/* interrupt request register */
>>  	u8 imr;		/* interrupt mask register */
>>  	u8 isr;		/* interrupt service register */
>> +	u8 isr_ack;	/* interrupt ack detection */
>>  	u8 priority_add;	/* highest irq priority */
>>  	u8 irq_base;
>>  	u8 read_reg_select;
>>   
>
> Needs to be cleared by reset 

@@ -213,6 +214,7 @@ void kvm_pic_reset(struct kvm_kpic_state
        s->irr = 0;
        s->imr = 0;
        s->isr = 0;
+       s->isr_ack = 0xff;
        s->priority_add = 0;
        s->irq_base = 0;
        s->read_reg_select = 0;

> and by register load from userspace, no?

Isnt that responsability of the guest? Unacked IOAPIC interrupts are not
cleared on register load, are they?