Re: [PATCH v4 3/4] KVM: x86: ioapic: Preserve irr_delivered for duplicate edge interrupts

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

On Tue, 2026-08-11 at 15:41 +0800, Hao Zhang wrote:
> From: Hao Zhang <zhanghao1@kylinos.cn>
> 
> For edge-triggered interrupts, ioapic_set_irq() clears irr_delivered
> before checking whether the new edge is a duplicate.  A duplicate edge
> is then coalesced without being serviced, leaving the interrupt visible
> in KVM_GET_IRQCHIP state even though the original interrupt was already
> delivered.
> 
> Move the state update after the duplicate-edge check so duplicate edges
> do not make a delivered interrupt appear pending during VM migration.

ioapic_set_irq() returns 0 for coalesced edge triggered IRQ, meaning it is
considered not delivered.  I don't see a problem if it is marked as pending in
ioapic->irr during KVM_GET_IRQCHIP for migration?  It seems the result is the
coalesced IRQ will get re-injected, but what's wrong of this?

But I am not sure on this, so will leave to maintainers.

> 
> Add a selftest to verify that a duplicate edge interrupt does not make
> an already-delivered interrupt visible in the saved IRR state.

IMO it's better to split kselftest changes to a separate patch out of KVM
changes.

> 
> Fixes: 5bda6eed2e36 ("KVM: ioapic: Record edge-triggered interrupts delivery status")

When this commit was merged, AFAICT the then ioapic_set_irq() didn't support
coalesced edge triggered IRQ at all, so technically this one shouldn't be the
one to blame.