Re: [PATCH v4 4/4] KVM: x86: ioapic: Clear irr_delivered on level-triggered RTE

["Huang, Kai" <kai.huang@intel.com>]

On Tue, 2026-08-11 at 15:43 +0800, Hao Zhang wrote:
> From: Hao Zhang <zhanghao1@kylinos.cn>
> 
> irr_delivered hides delivered edge interrupts from KVM_GET_IRQCHIP.
> The interrupt remains in IRR until the guest deasserts the line.
> 
> The guest can reprogram an IOAPIC RTE from edge to level via MMIO.
> If an edge interrupt was delivered before the trigger mode change, a
> stale irr_delivered bit can incorrectly mask a subsequent pending level
> interrupt from KVM_GET_IRQCHIP.
> 
> That can cause userspace to migrate the VM without a pending level
> interrupt that is still present in KVM's in-kernel IOAPIC.
> 

[...]

> --- a/arch/x86/kvm/ioapic.c
> +++ b/arch/x86/kvm/ioapic.c
> @@ -377,8 +377,17 @@ static void ioapic_write_indirect(struct kvm_ioapic *ioapic, u32 val)
>  		 * as edge-triggered. This behavior is used to simulate an
>  		 * explicit EOI on IOAPICs that don't have the EOI register.
>  		 */
> -		if (e->fields.trig_mode == IOAPIC_EDGE_TRIG)
> +		if (e->fields.trig_mode == IOAPIC_EDGE_TRIG) {
>  			e->fields.remote_irr = 0;
> +		} else {
> +			/*
> +			 * irr_delivered tracks edge-triggered interrupts that
> +			 * have already been delivered.  Clear stale edge-triggered
> +			 * delivery state when the entry is configured for
> +			 * level-triggered interrupts.
> +			 */
> +			ioapic->irr_delivered &= ~(1 << index);
> +		}

To be honest I am not sure whether we should consider this case, but IIUC this
code change doesn't seem to have any harm, so will leave to others.

>  
>  		mask_after = e->fields.mask;
>  		if (mask_before != mask_after)
> diff --git a/tools/testing/selftests/kvm/x86/ioapic_state_test.c b/tools/testing/selftests/kvm/x86/ioapic_state_test.c
> index da0276a1542f..f024f4f01571 100644
> --- a/tools/testing/selftests/kvm/x86/ioapic_state_test.c
> +++ b/tools/testing/selftests/kvm/x86/ioapic_state_test.c

Again, I think you should split selftest code change as a separate patch.

And it's better to have a cover letter for such series with multiple patches.