Re: [PATCH v5 3/6] KVM: x86: ioapic: Preserve irr_delivered for duplicate edge interrupts

On Thu, 2026-08-13 at 15:52 +0800, Hao Zhang wrote:
> > Could this sequence cause latched edge-triggered interrupts to be silently
> > ignored and lost if a guest temporarily masks IOAPIC pins during interrupt
> > handling?
> > 
> 
> Sashiko seems to assume that an edge-triggered interrupt which is signaled
> while the IOAPIC RTE is masked must remain latched and then be delivered when
> the RTE is unmasked.
> 
> However, the Intel 82093AA I/O Advanced Programmable Interrupt Controller datasheet
> (https://pdos.csail.mit.edu/6.828/2018/readings/ia32/ioapic.pdf) states that 
> edge-sensitive interrupts signaled on a masked interrupt pin are ignored, 
> i.e. they are not delivered or held pending.
> 
> KVM's userspace ABI (https://www.kernel.org/doc/html/v6.12/virt/kvm/api.html#kvm-irq-line) 
> also represents an edge interrupt as a pulse, by asserting the line and then deasserting 
> it. If that complete pulse occurs while the RTE is masked, there is no pending edge that 
> needs to be delivered on unmask.

+1.