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 07:16:34PM +0200, Avi Kivity wrote:
> On 03/30/2011 06:30 PM, 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>
> >
> >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);
> >
> 
> What about the check in inject_pending_events()?
> 
Didn't we decide that this check is not a problem? Worst that can happen
is NMI injection will be delayed till next exit.

--
			Gleb.