Re: [Xen-devel] xen/arm: GIC: unable to inject hw irq warning

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 3 Sep 2014, Vijay Kilari wrote:
> Hi Stefano,
> 
>  I face following warning messages for LPI/ITS interrupt.
> Can you throw some light on this warning?
> 
> (XEN) gic.c:394:d0v0 unable to inject hw irq=8736 into d0v0: already
> active in LR0
> (XEN) gic.c:394:d0v0 unable to inject hw irq=8736 into d0v0: already
> active in LR0
> (XEN) gic.c:394:d0v0 unable to inject hw irq=8736 into d0v0: already
> active in LR1
> (XEN) gic.c:394:d0v0 unable to inject hw irq=8736 into d0v0: already
> active in LR1
> (XEN) gic.c:394:d0v0 unable to inject hw irq=8736 into d0v0: already
> active in LR1
> (XEN) gic.c:394:d0v0 unable to inject hw irq=8736 into d0v0: already
> active in LR0

Hello Vijay,
the warning is for a condition that should not happen. All the following
must be true for the warning to trigger:

- the irq is an hardware irq (p->desc != NULL)

- the irq is active in the LR register (GICH_LR_ACTIVE)

- we need to inject a second irq while the first one is still active

The GICv2 specification explicitely states that it is not possible to
set an hardware irq as pending and active in the LR registers (5-175).

Regardless from the GICv2 specification, it shouldn't be possible to
receive a second hardware interrupt in Xen while the guest is still
handling the first one. So the question is: how is it possible that xen
is even trying to inject a second irq while the first one is still
active?  I would check how GIC_IRQ_GUEST_QUEUED was set.

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