Re: [PATCH] KVM: x86: Avoid busy loops over uninjectable pending APIC timers

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

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On 2013-03-17 09:47, Gleb Natapov wrote:
> On Sat, Mar 16, 2013 at 09:49:07PM +0100, Jan Kiszka wrote:
>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>
>> If the guest didn't take the last APIC timer interrupt yet and generates
>> another one on top, e.g. via periodic mode, we do not block the VCPU
>> even if the guest state is halted. The reason is that
>> apic_has_pending_timer continues to return a non-zero value.
>>
>> Fix this busy loop by taking the IRR content for the LVT vector in
>> apic_has_pending_timer into account.
>>
> Just drop coalescing tacking for lapic interrupt. After posted interrupt
> will be merged __apic_accept_irq() will not longer return coalescing
> information, so the code will be dead anyway.

If I understood the follow-up discussion correctly, we aren't dropping
de-coalescing support yet. So how to proceed with this fix here?

Jan

> 
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>> ---
>>
>> Not a critical issue, we are looping fully interruptible, but it's ugly
>> to do so IMHO.
>>
>>  arch/x86/kvm/lapic.c |    4 +++-
>>  1 files changed, 3 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>> index a8e9369..658abf5 100644
>> --- a/arch/x86/kvm/lapic.c
>> +++ b/arch/x86/kvm/lapic.c
>> @@ -1473,7 +1473,9 @@ int apic_has_pending_timer(struct kvm_vcpu *vcpu)
>>  	struct kvm_lapic *apic = vcpu->arch.apic;
>>  
>>  	if (kvm_vcpu_has_lapic(vcpu) && apic_enabled(apic) &&
>> -			apic_lvt_enabled(apic, APIC_LVTT))
>> +	    apic_lvt_enabled(apic, APIC_LVTT) &&
>> +	    !apic_test_vector(apic_lvt_vector(apic, APIC_LVTT),
>> +					      apic->regs + APIC_IRR))
>>  		return atomic_read(&apic->lapic_timer.pending);
>>  
>>  	return 0;
>> -- 
>> 1.7.3.4
> 
> --
> 			Gleb.



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