KVM: arm64: vgic: Don't acquire the lpi_list_lock in vgic_put_irq()

The LPI xarray's xa_lock is sufficient for synchronizing writers when
freeing a given LPI. Furthermore, readers can only take a new reference
on an IRQ if it was already nonzero.

Stop taking the lpi_list_lock unnecessarily and get rid of
__vgic_put_lpi_locked().

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240221054253.3848076-11-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: oupton

arch/arm64/kvm/vgic/vgic-its.c

@@ -649,7 +649,7 @@ static void vgic_its_cache_translation(struct kvm *kvm, struct vgic_its *its,
 	 * was in the cache, and increment it on the new interrupt.
 	 */
 	if (cte->irq)
-		__vgic_put_lpi_locked(kvm, cte->irq);
+		vgic_put_irq(kvm, cte->irq);
 
 	/*
 	 * The irq refcount is guaranteed to be nonzero while holding the
@@ -686,7 +686,7 @@ void vgic_its_invalidate_cache(struct kvm *kvm)
 		if (!cte->irq)
 			break;
 
-		__vgic_put_lpi_locked(kvm, cte->irq);
+		vgic_put_irq(kvm, cte->irq);
 		cte->irq = NULL;
 	}
 

arch/arm64/kvm/vgic/vgic.c

@@ -111,22 +111,6 @@ static void vgic_irq_release(struct kref *ref)
 {
 }
 
-/*
- * Drop the refcount on the LPI. Must be called with lpi_list_lock held.
- */
-void __vgic_put_lpi_locked(struct kvm *kvm, struct vgic_irq *irq)
-{
-	struct vgic_dist *dist = &kvm->arch.vgic;
-
-	if (!kref_put(&irq->refcount, vgic_irq_release))
-		return;
-
-	xa_erase(&dist->lpi_xa, irq->intid);
-	atomic_dec(&dist->lpi_count);
-
-	kfree_rcu(irq, rcu);
-}
-
 void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq)
 {
 	struct vgic_dist *dist = &kvm->arch.vgic;
@@ -135,9 +119,15 @@ void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq)
 	if (irq->intid < VGIC_MIN_LPI)
 		return;
 
-	raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
-	__vgic_put_lpi_locked(kvm, irq);
-	raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
+	if (!kref_put(&irq->refcount, vgic_irq_release))
+		return;
+
+	xa_lock_irqsave(&dist->lpi_xa, flags);
+	__xa_erase(&dist->lpi_xa, irq->intid);
+	xa_unlock_irqrestore(&dist->lpi_xa, flags);
+
+	atomic_dec(&dist->lpi_count);
+	kfree_rcu(irq, rcu);
 }
 
 void vgic_flush_pending_lpis(struct kvm_vcpu *vcpu)

arch/arm64/kvm/vgic/vgic.h

@@ -180,7 +180,6 @@ vgic_get_mmio_region(struct kvm_vcpu *vcpu, struct vgic_io_device *iodev,
 		     gpa_t addr, int len);
 struct vgic_irq *vgic_get_irq(struct kvm *kvm, struct kvm_vcpu *vcpu,
 			      u32 intid);
-void __vgic_put_lpi_locked(struct kvm *kvm, struct vgic_irq *irq);
 void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq);
 bool vgic_get_phys_line_level(struct vgic_irq *irq);
 void vgic_irq_set_phys_pending(struct vgic_irq *irq, bool pending);