Re: KVM: x86: better fix for race between nmi injection and enabling nmi window

[Gleb Natapov <gleb@redhat.com>]

On Wed, Mar 30, 2011 at 01:30:28PM -0300, Marcelo Tosatti wrote:
> 
> Based on Gleb's idea, fix race between nmi injection and enabling 
> nmi window in a simpler way.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
But we need to revert the patch that introduced use of request for NMI
first.  Otherwise NMI will not be delivered, no?

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a6a129f..9a7cc1be 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5152,6 +5152,7 @@ static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
>  static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  {
>  	int r;
> +	int nmi_pending;
>  	bool req_int_win = !irqchip_in_kernel(vcpu->kvm) &&
>  		vcpu->run->request_interrupt_window;
>  
> @@ -5195,11 +5196,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  	if (unlikely(r))
>  		goto out;
>  
> +	nmi_pending = ACCESS_ONCE(vcpu->arch.nmi_pending);
> +
>  	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
>  		inject_pending_event(vcpu);
>  
>  		/* enable NMI/IRQ window open exits if needed */
> -		if (vcpu->arch.nmi_pending)
> +		if (nmi_pending)
>  			kvm_x86_ops->enable_nmi_window(vcpu);
>  		else if (kvm_cpu_has_interrupt(vcpu) || req_int_win)
>  			kvm_x86_ops->enable_irq_window(vcpu);

--
			Gleb.