KVM: arm64: Invert ap_list sorting to push active interrupts out

Having established that pending interrupts should have priority
to be moved into the LRs over the active interrupts, implement this
in the ap_list sorting.

Tested-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Link: https://msgid.link/20251120172540.2267180-25-maz@kernel.org
Signed-off-by: Oliver Upton <oupton@kernel.org>

1 files changed, 12 insertions, 15 deletions

diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index 004010104659..c7a5454ac4c9 100644
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c
@@ -270,10 +270,7 @@ struct kvm_vcpu *vgic_target_oracle(struct vgic_irq *irq)
  * well, the first items in the list being the first things populated in the
  * LRs.
  *
- * A hard rule is that active interrupts can never be pushed out of the LRs
- * (and therefore take priority) since we cannot reliably trap on deactivation
- * of IRQs and therefore they have to be present in the LRs.
- *
+ * Pending, non-active interrupts must be placed at the head of the list.
  * Otherwise things should be sorted by the priority field and the GIC
  * hardware support will take care of preemption of priority groups etc.
  *
@@ -298,21 +295,21 @@ static int vgic_irq_cmp(void *priv, const struct list_head *a,
 	raw_spin_lock(&irqa->irq_lock);
 	raw_spin_lock_nested(&irqb->irq_lock, SINGLE_DEPTH_NESTING);
 
-	if (irqa->active || irqb->active) {
-		ret = (int)irqb->active - (int)irqa->active;
-		goto out;
-	}
+	penda = irqa->enabled && irq_is_pending(irqa) && !irqa->active;
+	pendb = irqb->enabled && irq_is_pending(irqb) && !irqb->active;
 
-	penda = irqa->enabled && irq_is_pending(irqa);
-	pendb = irqb->enabled && irq_is_pending(irqb);
+	ret = (int)pendb - (int)penda;
+	if (ret)
+		goto out;
 
-	if (!penda || !pendb) {
-		ret = (int)pendb - (int)penda;
+	/* Both pending and enabled, sort by priority (lower number first) */
+	ret = (int)irqa->priority - (int)irqb->priority;
+	if (ret)
 		goto out;
-	}
 
-	/* Both pending and enabled, sort by priority */
-	ret = irqa->priority - irqb->priority;
+	/* Finally, HW bit active interrupts have priority over non-HW ones */
+	ret = (int)irqb->hw - (int)irqa->hw;
+
 out:
 	raw_spin_unlock(&irqb->irq_lock);
 	raw_spin_unlock(&irqa->irq_lock);