Re: [Qemu-devel] [PATCH for 2.8?] x86: ioapic: ignore level irq during processing

[Paolo Bonzini <pbonzini@redhat.com>]

On 31/07/2016 16:18, Peter Xu wrote:
> For level triggered interrupts, we will get Remote IRR bit cleared after
> guest kernel finished processing specific request. Before that, we
> should ignore the same interrupt from triggering again.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> 
> I discovered this during debugging some IR issues. Only did very
> minimum test with e1000, but IIUC this should be the correct behavior
> for level triggered interrupts, and before that we might be sending
> some extra interrupts to guest (while we should not).
> 
>  hw/intc/ioapic.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/intc/ioapic.c b/hw/intc/ioapic.c
> index 2d3282a..350f761 100644
> --- a/hw/intc/ioapic.c
> +++ b/hw/intc/ioapic.c
> @@ -129,9 +129,15 @@ static void ioapic_service(IOAPICCommonState *s)
>                      }
>                      continue;
>                  }
> -#else
> -                (void)coalesce;
>  #endif
> +
> +                if (coalesce) {
> +                    /* We are level triggered interrupts, and the
> +                     * guest should be still working on previous one,
> +                     * so skip it. */
> +                    continue;
> +                }
> +
>                  /* No matter whether IR is enabled, we translate
>                   * the IOAPIC message into a MSI one, and its
>                   * address space will decide whether we need a
> 

The patch is okay for 2.7, as it matches what is done in the KVM
split-irqchip case.

Paolo