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

[Gleb Natapov <gleb@redhat.com>]

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.

> 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.