Re: [PATCH 16/32] KVM: arm64: gic: Introduce irq_queue and set_pending_state to irq_ops

There are times when the default behaviour of vgic_queue_irq_unlock is
undesirable. This is because some GICs, such a GICv5 which is the main
driver for this change, handle the majority of the interrupt lifecycle
in hardware. In this case, there is no need for a per-VCPU AP list as
the interrupt can be made pending directly. This is done either via
the ICH_PPI_x_EL2 registers for PPIs, or with the VDPEND system
instruction for SPIs and LPIs.

The queue_irq_unlock function is made overridable using a new function
pointer in struct irq_ops. In kvm_vgic_inject_irq,
vgic_queue_irq_unlock is overridden if the function pointer is
non-null.

Additionally, a new function is added via a function pointer -
set_pending_state. The intent is for this to be used to directly set
the pending state in hardware.

Both of these new irq_ops are unused in this change - it is purely
providing the infrastructure itself. The subsequent PPI injection
changes provide a demonstration of their usage.

Signed-off-by: Sascha Bischoff <redacted>
---
 arch/arm64/kvm/vgic/vgic.c |  9 ++++++++-
 include/kvm/arm_vgic.h     | 15 +++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index 1fe3dcc997860..fc01c6d07fe62 100644
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c

@@ -547,7 +547,14 @@ int kvm_vgic_inject_irq(struct kvm *kvm, struct kvm_vcpu *vcpu,
 	else
 		irq->pending_latch = true;
 
-	vgic_queue_irq_unlock(kvm, irq, flags);
+	if (irq->ops && irq->ops->set_pending_state)
+		WARN_ON_ONCE(!irq->ops->set_pending_state(vcpu, irq));
+
+	if (irq->ops && irq->ops->queue_irq_unlock)
+		WARN_ON_ONCE(!irq->ops->queue_irq_unlock(kvm, irq, flags));
+	else
+		vgic_queue_irq_unlock(kvm, irq, flags);