[PATCH 3/8] KVM: arm/arm64: vgic-its: Cache successful MSI->LPI translation

[Marc Zyngier <marc.zyngier@arm.com>]

On a successful translation, preserve the parameters in the LPI
translation cache. Each translation is reusing the last slot
in the list, naturally evincting the least recently used entry.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 virt/kvm/arm/vgic/vgic-its.c | 41 ++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
index 5758504fd934..bc370b6c5afa 100644
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -538,6 +538,45 @@ static unsigned long vgic_mmio_read_its_idregs(struct kvm *kvm,
 	return 0;
 }
 
+static void vgic_its_cache_translation(struct kvm *kvm, struct vgic_its *its,
+				       u32 devid, u32 eventid,
+				       struct vgic_irq *irq)
+{
+	struct vgic_dist *dist = &kvm->arch.vgic;
+	struct vgic_translation_cache_entry *cte;
+	unsigned long flags;
+
+	/* Do not cache a directly injected interrupt */
+	if (irq->hw)
+		return;
+
+	raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
+
+	/* Always reuse the last entry (LRU policy) */
+	cte = list_last_entry(&dist->lpi_translation_cache,
+			      typeof(*cte), entry);
+
+	/*
+	 * Caching the translation implies having an extra reference
+	 * to the interrupt, so drop the potential reference on what
+	 * was in the cache, and increment it on the new interrupt.
+	 */
+	if (cte->irq)
+		__vgic_put_lpi_locked(kvm, cte->irq);
+
+	vgic_get_irq_kref(irq);
+
+	cte->db		= its->vgic_its_base + GITS_TRANSLATER;
+	cte->devid	= devid;
+	cte->eventid	= eventid;
+	cte->irq	= irq;
+
+	/* Move the new translation to the head of the list */
+	list_move(&cte->entry, &dist->lpi_translation_cache);
+
+	raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
+}
+
 int vgic_its_resolve_lpi(struct kvm *kvm, struct vgic_its *its,
 			 u32 devid, u32 eventid, struct vgic_irq **irq)
 {
@@ -558,6 +597,8 @@ int vgic_its_resolve_lpi(struct kvm *kvm, struct vgic_its *its,
 	if (!vcpu->arch.vgic_cpu.lpis_enabled)
 		return -EBUSY;
 
+	vgic_its_cache_translation(kvm, its, devid, eventid, ite->irq);
+
 	*irq = ite->irq;
 	return 0;
 }
-- 
2.20.1

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