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

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On 03/30/2011 08:47 PM, 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@xxxxxxxxxx>
>  >
>  >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.

Could be very far in the future.

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

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