Re: [PATCH] KVM: x86: Convert INIT and SIPI signals into synchronously handled events

[Jan Kiszka <jan.kiszka@web.de>]

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On 2013-03-12 13:06, Paolo Bonzini wrote:
>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>> index 02b51dd..4a21a6b 100644
>> --- a/arch/x86/kvm/lapic.c
>> +++ b/arch/x86/kvm/lapic.c
>> @@ -731,7 +731,7 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
>>  	case APIC_DM_INIT:
>>  		if (!trig_mode || level) {
>>  			result = 1;
>> -			vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
>> +			set_bit(KVM_APIC_INIT, &apic->pending_events);
> 
> I think this should clear pending SIPIs, unless KVM_APIC_INIT was
> already set in which case it should be a no-op.  Something like:
> 
> 	e = apic->pending_events;
> 	while (!(e & KVM_APIC_INIT))
> 		e = cmpxchg(&apic->pending_events, e,
> 			    (e | KVM_APIC_INIT) & ~KVM_APIC_SIPI);
> 
> If you do this, better make pending_events an atomic_t.

Quick question: Why atomic_t? It becomes a bit ugly to poke into the
atomic counter for bitops, and cmpxchg is mapped on an interlocked version.

Jan



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