Re: [PATCH 3/3] KVM: x86: Optimize NMI watchdog delivery

[Sheng Yang <yasker@gmail.com>]

On Wed, Oct 15, 2008 at 04:27:51PM +0200, Jan Kiszka wrote:
> As suggested by Avi, this patch introduces a counter of VCPUs that have
> LVT0 set to NMI mode. Only if the counter > 0, we push the PIT ticks via
> all LAPIC LVT0 lines to enable NMI watchdog support.
> 

I feel a little strange about: if *counter > 0*, we push to *all*. Can we
only push NMIs to the ones that set NMI for LVT0?

How about add a field in struct kvm_lapic? We can quickly know if we need to
inject NMI for this vcpu. Well, though kernel mostly enable NMI watchdog on
all vcpu, I think this is more precise, and match the logic, and avoid one
more field in kvm_arch...

--
regards
Yang, Sheng

> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>  arch/x86/kvm/i8254.c       |   13 +++++++------
>  arch/x86/kvm/lapic.c       |   23 ++++++++++++++++++++---
>  include/asm-x86/kvm_host.h |    1 +
>  3 files changed, 28 insertions(+), 9 deletions(-)
> 
> Index: b/arch/x86/kvm/i8254.c
> ===================================================================
> --- a/arch/x86/kvm/i8254.c
> +++ b/arch/x86/kvm/i8254.c
> @@ -607,12 +607,13 @@ static void __inject_pit_timer_intr(stru
>  	 * 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 || !kvm_apic_accept_pic_intr(vcpu))
> -			continue;
> -		kvm_apic_local_deliver(vcpu, APIC_LVT0);
> -	}
> +	if (kvm->arch.vapics_in_nmi_mode > 0)
> +		for (i = 0; i < KVM_MAX_VCPUS; ++i) {
> +			vcpu = kvm->vcpus[i];
> +			if (!vcpu || !kvm_apic_accept_pic_intr(vcpu))
> +				continue;
> +			kvm_apic_local_deliver(vcpu, APIC_LVT0);
> +		}
>  }
>  
>  void kvm_inject_pit_timer_irqs(struct kvm_vcpu *vcpu)
> Index: b/arch/x86/kvm/lapic.c
> ===================================================================
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -130,6 +130,11 @@ static inline int apic_lvtt_period(struc
>  	return apic_get_reg(apic, APIC_LVTT) & APIC_LVT_TIMER_PERIODIC;
>  }
>  
> +static inline int apic_lvt_nmi_mode(u32 lvt_val)
> +{
> +	return (lvt_val & (APIC_MODE_MASK | APIC_LVT_MASKED)) == APIC_DM_NMI;
> +}
> +
>  static unsigned int apic_lvt_mask[APIC_LVT_NUM] = {
>  	LVT_MASK | APIC_LVT_TIMER_PERIODIC,	/* LVTT */
>  	LVT_MASK | APIC_MODE_MASK,	/* LVTTHMR */
> @@ -672,6 +677,20 @@ static void start_apic_timer(struct kvm_
>  					apic->timer.period)));
>  }
>  
> +static void apic_manage_nmi_watchdog(struct kvm_lapic *apic, u32 lvt0_val)
> +{
> +	int nmi_wd_enabled = apic_lvt_nmi_mode(apic_get_reg(apic, APIC_LVT0));
> +
> +	if (apic_lvt_nmi_mode(lvt0_val)) {
> +		if (!nmi_wd_enabled) {
> +			apic_debug("Receive NMI setting on APIC_LVT0 "
> +				   "for cpu %d\n", apic->vcpu->vcpu_id);
> +			apic->vcpu->kvm->arch.vapics_in_nmi_mode++;
> +		}
> +	} else if (nmi_wd_enabled)
> +		apic->vcpu->kvm->arch.vapics_in_nmi_mode--;
> +}
> +
>  static void apic_mmio_write(struct kvm_io_device *this,
>  			    gpa_t address, int len, const void *data)
>  {
> @@ -753,9 +772,7 @@ static void apic_mmio_write(struct kvm_i
>  		break;
>  
>  	case APIC_LVT0:
> -		if (val == APIC_DM_NMI)
> -			apic_debug("Receive NMI setting on APIC_LVT0 "
> -				"for cpu %d\n", apic->vcpu->vcpu_id);
> +		apic_manage_nmi_watchdog(apic, val);
>  	case APIC_LVTT:
>  	case APIC_LVTTHMR:
>  	case APIC_LVTPC:
> Index: b/include/asm-x86/kvm_host.h
> ===================================================================
> --- a/include/asm-x86/kvm_host.h
> +++ b/include/asm-x86/kvm_host.h
> @@ -359,6 +359,7 @@ struct kvm_arch{
>  	struct kvm_ioapic *vioapic;
>  	struct kvm_pit *vpit;
>  	struct hlist_head irq_ack_notifier_list;
> +	int vapics_in_nmi_mode;
>  
>  	int round_robin_prev_vcpu;
>  	unsigned int tss_addr;
> 
> --
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