Re: [PATCH for-4.14 v2 2/2] x86/passthrough: introduce a flag for GSIs not requiring an EOI or unmask

[Jan Beulich <jbeulich@suse.com>]

On 10.06.2020 16:29, Roger Pau Monne wrote:
> @@ -558,6 +559,12 @@ int pt_irq_create_bind(
>                       */
>                      ASSERT(!mask);
>                      share = trigger_mode;
> +                    if ( trigger_mode == VIOAPIC_EDGE_TRIG )
> +                        /*
> +                         * Edge IO-APIC interrupt, no EOI or unmask to perform
> +                         * and hence no timer needed.
> +                         */
> +                        pirq_dpci->flags |= HVM_IRQ_DPCI_NO_EOI;

Is this really limited to edge triggered IO-APIC interrupts?
MSI ones are effectively edge triggered too, aren't they?
Along the lines of irq_acktype() maskable MSI may then also
not need any such arrangements? The pirq_guest_eoi() ->
desc_guest_eoi() path looks to confirm this.

> @@ -920,6 +923,8 @@ static void hvm_dirq_assist(struct domain *d, struct hvm_pirq_dpci *pirq_dpci)
>          if ( pirq_dpci->flags & HVM_IRQ_DPCI_IDENTITY_GSI )
>          {
>              hvm_gsi_assert(d, pirq->pirq);
> +            if ( pirq_dpci->flags & HVM_IRQ_DPCI_NO_EOI )
> +                goto out;

Immediately ahead of this there's a similar piece of code
dealing with PCI INTx. They're commonly level triggered, but
I don't think there's a strict need for this to be the case.
At least hvm_pci_intx_assert() -> assert_gsi() ->
vioapic_irq_positive_edge() also cover the edge triggered one.

Jan