Re: [Qemu-devel] [PATCH 1/1 V5 tuning] kernel/kvm: introduce KVM_SET_LINT1 and fix improper nmi emulation

[Jan Kiszka]

On 2011-10-14 13:59, Sasha Levin wrote:
> On Fri, 2011-10-14 at 17:51 +0800, Lai Jiangshan wrote:
>> 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 masked 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, we introduce introduce KVM_SET_LINT1,
>> and we can use KVM_SET_LINT1 to correctly emulate NMI button
>> without change the old KVM_NMI behavior.
>>
>> Signed-off-by: Lai Jiangshan <address@hidden>
>> Reported-by: Kenji Kaneshige <address@hidden>
>> ---
> 
> It could use a documentation update as well.
> 
>>  arch/x86/kvm/irq.h   |    1 +
>>  arch/x86/kvm/lapic.c |    7 +++++++
>>  arch/x86/kvm/x86.c   |    8 ++++++++
>>  include/linux/kvm.h  |    3 +++
>>  4 files changed, 19 insertions(+), 0 deletions(-)
>> 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..fccd094 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -2077,6 +2077,7 @@ int kvm_dev_ioctl_check_extension(long ext)
>>      case KVM_CAP_XSAVE:
>>      case KVM_CAP_ASYNC_PF:
>>      case KVM_CAP_GET_TSC_KHZ:
>> +    case KVM_CAP_SET_LINT1:
>>              r = 1;
>>              break;
>>      case KVM_CAP_COALESCED_MMIO:
>> @@ -3264,6 +3265,13 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>>  
>>              goto out;
>>      }
>> +    case KVM_SET_LINT1: {
>> +            r = -EINVAL;
>> +            if (!irqchip_in_kernel(vcpu->kvm))
>> +                    goto out;
>> +            r = 0;
>> +            kvm_apic_lint1_deliver(vcpu);
> 
> We simply ignore the return value of kvm_apic_local_deliver() and assume
> it always works. why?
> 

Hmm, I suddenly realized that we switched from enhancing the KVM_NMI
IOCTL to adding KVM_SET_LINT1 - what motivated this?

( Maybe we should let the kernel part settle first before iterating
through user space changes. )

Jan

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