Re: [PATCH 1/1 V2] kernel/kvm: fix improper nmi emulation

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(2011/10/12 2:00), Lai Jiangshan wrote:
> From: Kenji Kaneshige<kaneshige.kenji@xxxxxxxxxxxxxx>
> 
> Currently, NMI interrupt is blindly sent to all the vCPUs when NMI
> button event happens. This doesn't properly emulate real hardware on
> which NMI button event triggers LINT1. Because of this, NMI is sent to
> the processor even when LINT1 is maskied in LVT. For example, this
> causes the problem that kdump initiated by NMI sometimes doesn't work
> on KVM, because kdump assumes NMI is masked on CPUs other than CPU0.
> 
> With this patch, KVM_NMI ioctl is handled as follows.
> 
> - When in-kernel irqchip is enabled, KVM_NMI ioctl is handled as a
>    request of triggering LINT1 on the processor. LINT1 is emulated in
>    in-kernel irqchip.
> 
> - When in-kernel irqchip is disabled, KVM_NMI ioctl is handled as a
>    request of injecting NMI to the processor. This assumes LINT1 is
>    already emulated in userland.
> 
> (laijs) Changed from v1:
> Add KVM_NMI API document
> Add KVM_CAP_USER_NMI
> 
> Signed-off-by: Kenji Kaneshige<kaneshige.kenji@xxxxxxxxxxxxxx>
> Tested-by: Lai Jiangshan<laijs@xxxxxxxxxxxxxx>
> ---
>   Documentation/virtual/kvm/api.txt |   20 ++++++++++++++++++++
>   arch/x86/kvm/irq.h                |    1 +
>   arch/x86/kvm/lapic.c              |    7 +++++++
>   arch/x86/kvm/x86.c                |   12 ++++++++++++
>   include/linux/kvm.h               |    3 +++
>   5 files changed, 43 insertions(+), 0 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index b0e4b9c..5c24cc3 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -1430,6 +1430,26 @@ is supported; 2 if the processor requires all virtual machines to have
>   an RMA, or 1 if the processor can use an RMA but doesn't require it,
>   because it supports the Virtual RMA (VRMA) facility.
> 
> +4.64 KVM_NMI
> +
> +Capability: KVM_CAP_USER_NMI
> +Architectures: x86
> +Type: vcpu ioctl
> +Parameters: none
> +Returns: 0 on success, -1 on error
> +
> +This ioctl injects NMI to the vcpu.
> +
> +If with capability KVM_CAP_LAPIC_NMI, KVM_NMI ioctl is handled as follows:
> +
> +	- When in-kernel irqchip is enabled, KVM_NMI ioctl is handled as a
> +	  request of triggering LINT1 on the processor. LINT1 is emulated in
> +	  in-kernel lapic irqchip.
> +
> +	- When in-kernel irqchip is disabled, KVM_NMI ioctl is handled as a
> +	  request of injecting NMI to the processor. This assumes LINT1 is
> +	  already emulated in userland lapic.
> +
>   5. The kvm_run structure
> 
>   Application code obtains a pointer to the kvm_run structure by
> diff --git a/arch/x86/kvm/irq.h b/arch/x86/kvm/irq.h
> index 53e2d08..0c96315 100644
> --- a/arch/x86/kvm/irq.h
> +++ b/arch/x86/kvm/irq.h
> @@ -95,6 +95,7 @@ void kvm_pic_reset(struct kvm_kpic_state *s);
>   void kvm_inject_pending_timer_irqs(struct kvm_vcpu *vcpu);
>   void kvm_inject_apic_timer_irqs(struct kvm_vcpu *vcpu);
>   void kvm_apic_nmi_wd_deliver(struct kvm_vcpu *vcpu);
> +void kvm_apic_lint1_deliver(struct kvm_vcpu *vcpu);
>   void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu);
>   void __kvm_migrate_pit_timer(struct kvm_vcpu *vcpu);
>   void __kvm_migrate_timers(struct kvm_vcpu *vcpu);
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 57dcbd4..87fe36a 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1039,6 +1039,13 @@ void kvm_apic_nmi_wd_deliver(struct kvm_vcpu *vcpu)
>   		kvm_apic_local_deliver(apic, APIC_LVT0);
>   }
> 
> +void kvm_apic_lint1_deliver(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_lapic *apic = vcpu->arch.apic;
> +
> +	kvm_apic_local_deliver(apic, APIC_LVT1);
> +}
> +
>   static struct kvm_timer_ops lapic_timer_ops = {
>   	.is_periodic = lapic_is_periodic,
>   };
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 84a28ea..6862ef7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2729,12 +2729,24 @@ static int kvm_vcpu_ioctl_interrupt(struct kvm_vcpu *vcpu,
>   	return 0;
>   }
> 
> +#ifdef KVM_CAP_LAPIC_NMI
> +static int kvm_vcpu_ioctl_nmi(struct kvm_vcpu *vcpu)
> +{
> +	if (irqchip_in_kernel(vcpu->kvm))
> +		kvm_apic_lint1_deliver(vcpu);
> +	else
> +		kvm_inject_nmi(vcpu);
> +
> +	return 0;
> +}
> +#else
>   static int kvm_vcpu_ioctl_nmi(struct kvm_vcpu *vcpu)
>   {
>   	kvm_inject_nmi(vcpu);
> 
>   	return 0;
>   }
> +#endif

I don't think we need to keep old kvm_vcpu_ioctl_nmi() behavior because
it's clearly a bug.

Regards,
Kenji Kaneshige
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