Re: [PATCH 08/14] KVM: x86: Enable NMI Watchdog via in-kernel PIT source

[Avi Kivity <avi@redhat.com>]

jan.kiszka@siemens.com wrote:
> LINT0 of the LAPIC can be used to route PIT events as NMI watchdog ticks
> into the guest. This patch aligns the in-kernel irqchip emulation with
> the user space irqchip with already supports this feature. The trick is
> to route PIT interrupts to all LAPIC's LVT0 lines.
>
> Rebased and slightly polished patch originally posted by Sheng Yang.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> Signed-off-by: Sheng Yang <sheng.yang@intel.com>
> ---
>  arch/x86/kvm/i8254.c |   15 +++++++++++++++
>  arch/x86/kvm/irq.h   |    1 +
>  arch/x86/kvm/lapic.c |   34 +++++++++++++++++++++++++++++-----
>  3 files changed, 45 insertions(+), 5 deletions(-)
>
> Index: b/arch/x86/kvm/i8254.c
> ===================================================================
> --- a/arch/x86/kvm/i8254.c
> +++ b/arch/x86/kvm/i8254.c
> @@ -594,10 +594,25 @@ void kvm_free_pit(struct kvm *kvm)
>  
>  static void __inject_pit_timer_intr(struct kvm *kvm)
>  {
> +	struct kvm_vcpu *vcpu;
> +	int i;
> +
>  	mutex_lock(&kvm->lock);
>  	kvm_set_irq(kvm, 0, 1);
>  	kvm_set_irq(kvm, 0, 0);
>  	mutex_unlock(&kvm->lock);
> +
> +	/*
> +	 * Provides NMI watchdog support in IOAPIC mode.
> +	 * The route is: PIT -> PIC -> LVT0 in NMI mode,
> +	 * timer IRQs will continue to flow through the IOAPIC.
> +	 */
> +	for (i = 0; i < KVM_MAX_VCPUS; ++i) {
> +		vcpu = kvm->vcpus[i];
> +		if (!vcpu)
> +			continue;
> +		kvm_apic_local_deliver(vcpu, APIC_LVT0);
> +	}
>  }
>   

It would be better to gate this on a variable which is set only if this 
is actually necessary (e.g, does any vcpu have LVT0 set to NMI mode).  
Otherwise, we touch all vcpus up to 1000 times a second.  As this is an 
optimization, it can be done later.


-- 
error compiling committee.c: too many arguments to function