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

[Marcelo Tosatti <mtosatti@redhat.com>]

On Wed, Mar 30, 2011 at 08:47:03PM +0200, Gleb Natapov wrote:
> 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.

Yes.