Re: [PATCH v2] KVM: Fix simultaneous NMIs

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On 09/20/2011 05:59 PM, Marcelo Tosatti wrote:
On Tue, Sep 20, 2011 at 04:56:02PM +0300, Avi Kivity wrote:
>  On 09/20/2011 04:25 PM, Marcelo Tosatti wrote:
>  >>
>  >>   @@ -2827,6 +2828,7 @@ static int kvm_vcpu_ioctl_x86_set_mce(struct kvm_vcpu *vcpu,
>  >>    static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
>  >>    					struct kvm_vcpu_events *events)
>  >>    {
>  >>   +	process_nmi(vcpu);
>  >>    	events->exception.injected =
>  >>    		vcpu->arch.exception.pending&&
>  >>    		!kvm_exception_is_soft(vcpu->arch.exception.nr);
>  >>   @@ -2844,7 +2846,7 @@ static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
>  >>    			KVM_X86_SHADOW_INT_MOV_SS | KVM_X86_SHADOW_INT_STI);
>  >>
>  >>    	events->nmi.injected = vcpu->arch.nmi_injected;
>  >>   -	events->nmi.pending = vcpu->arch.nmi_pending;
>  >>   +	events->nmi.pending = vcpu->arch.nmi_pending != 0;
>  >>    	events->nmi.masked = kvm_x86_ops->get_nmi_mask(vcpu);
>  >>    	events->nmi.pad = 0;
>  >
>  >nmi_queued should also be saved and restored. Not sure if its necessary
>  >though.
>  >
>  >Should at least reset nmi_queued somewhere (set_vcpu_events?).
>
>  Did you miss the call to process_nmi()?

It transfers nmi_queued to nmi_pending with capping. What i mean is that
upon system reset, nmi_queued (which refers to pre-reset system state)
should be zeroed.

The is get_events(); for set_events(), process_nmi() does zero nmi_queued() (and then we overwrite nmi_pending).


>  We do have a small issue.  If we exit during NMI-blocked-by-STI and
>  nmi_pending == 2, then we lose the second interrupt.  Should rarely
>  happen, since external interrupts never exit in that condition, but
>  it's a wart.

And the above system reset case, you should be able to handle it by
saving/restoring nmi_queued (so that QEMU can zero it in vcpu_reset).

We could just add a KVM_CAP (and flag) that extends nmi_pending from a bool to a counter.




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

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