Re: [RFC][PATCH 3/4] KVM: VMX: Enable NMI with in-kernel irqchip

Avi Kivity
2008-05-12T07:54:00Z

Yang, Sheng wrote:
> On Friday 09 May 2008 23:49:13 Avi Kivity wrote:
>
>> Yang, Sheng wrote:
>>
>>> From 4942a5c35c97e5edb6fe1303e04fb86f25cac345 Mon Sep 17 00:00:00 2001
>>> From: Sheng Yang <sheng.yang@intel.com>
>>> Date: Thu, 8 May 2008 16:00:57 +0800
>>> Subject: [PATCH 3/4] KVM: VMX: Enable NMI with in-kernel irqchip
>>>
>>>
>>> static void kvm_do_inject_irq(struct kvm_vcpu *vcpu)
>>> {
>>> int word_index = __ffs(vcpu->arch.irq_summary);
>>> @@ -2146,9 +2159,11 @@ static void do_interrupt_requests(struct kvm_vcpu
>>> *vcpu,
>>> /*
>>> * Interrupts blocked. Wait for unblock.
>>> */
>>> - cpu_based_vm_exec_control |= CPU_BASED_VIRTUAL_INTR_PENDING;
>>> + cpu_based_vm_exec_control |=
>>> + CPU_BASED_VIRTUAL_INTR_PENDING;
>>> else
>>> - cpu_based_vm_exec_control &= ~CPU_BASED_VIRTUAL_INTR_PENDING;
>>> + cpu_based_vm_exec_control &=
>>> + ~CPU_BASED_VIRTUAL_INTR_PENDING;
>>>
>> This seems spurious.
>>
>
> Sorry, seems I am too anxious to keep it in hand... I would like to check it
> much careful in the future.
>
>
>>> /* We need to handle NMIs before interrupts are enabled */
>>> - if ((intr_info & INTR_INFO_INTR_TYPE_MASK) == 0x200) { /* nmi */
>>> + if ((intr_info & INTR_INFO_INTR_TYPE_MASK) == 0x200) {
>>> KVMTRACE_0D(NMI, vcpu, handler);
>>> - asm("int $2");
>>> + if (!cpu_has_virtual_nmis())
>>> + asm("int $2");
>>> }
>>> }
>>>
>> That's a host nmi. So does the PIN_BASED_VIRTUAL_NMI mean NMIs are
>> handled like unacked host interrupts?
>>
>
> Not exactly. No host NMI here if Virtual_NMI is set. Copy from SDM 3B table
> 20-5:
>
> "If this control(Virtual NMIs) is 1, NMIs are never blocked and the “blocking
> by NMI” bit (bit 3) in the interruptibility-state field
> indicates “virtual-NMI blocking” (see Table 20-3). This control also
> interacts with the “NMI-window exiting” VM-execution control (see Section
> 20.6.2)."
>

I still don't understand. What does "NMIs are never blocked" mean?
what happens if an NMI occurs while in guest mode? Obviously we don't
want it to be delivered to the guest.

--
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