KVM: arm64: vgic-v3: Use bare refcount for VGIC LPIs

KVM's use of krefs to manage LPIs isn't adding much, especially
considering vgic_irq_release() is a noop due to the lack of sufficient
context.

Switch to using a regular refcount in anticipation of adding a
meaningful release concept for LPIs.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250905100531.282980-3-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

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

@@ -69,7 +69,7 @@ static int iter_mark_lpis(struct kvm *kvm)
 	int nr_lpis = 0;
 
 	xa_for_each(&dist->lpi_xa, intid, irq) {
-		if (!vgic_try_get_irq_kref(irq))
+		if (!vgic_try_get_irq_ref(irq))
 			continue;
 
 		xa_set_mark(&dist->lpi_xa, intid, LPI_XA_MARK_DEBUG_ITER);

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

@@ -208,7 +208,7 @@ static int kvm_vgic_dist_init(struct kvm *kvm, unsigned int nr_spis)
 		raw_spin_lock_init(&irq->irq_lock);
 		irq->vcpu = NULL;
 		irq->target_vcpu = vcpu0;
-		kref_init(&irq->refcount);
+		refcount_set(&irq->refcount, 0);
 		switch (dist->vgic_model) {
 		case KVM_DEV_TYPE_ARM_VGIC_V2:
 			irq->targets = 0;
@@ -277,7 +277,7 @@ static int vgic_allocate_private_irqs_locked(struct kvm_vcpu *vcpu, u32 type)
 		irq->intid = i;
 		irq->vcpu = NULL;
 		irq->target_vcpu = vcpu;
-		kref_init(&irq->refcount);
+		refcount_set(&irq->refcount, 0);
 		if (vgic_irq_is_sgi(i)) {
 			/* SGIs */
 			irq->enabled = 1;

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

@@ -99,7 +99,7 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid,
 	raw_spin_lock_init(&irq->irq_lock);
 
 	irq->config = VGIC_CONFIG_EDGE;
-	kref_init(&irq->refcount);
+	refcount_set(&irq->refcount, 1);
 	irq->intid = intid;
 	irq->target_vcpu = vcpu;
 	irq->group = 1;
@@ -111,7 +111,7 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid,
 	 * check that we don't add a second list entry with the same LPI.
 	 */
 	oldirq = xa_load(&dist->lpi_xa, intid);
-	if (vgic_try_get_irq_kref(oldirq)) {
+	if (vgic_try_get_irq_ref(oldirq)) {
 		/* Someone was faster with adding this LPI, lets use that. */
 		kfree(irq);
 		irq = oldirq;
@@ -547,7 +547,7 @@ static struct vgic_irq *vgic_its_check_cache(struct kvm *kvm, phys_addr_t db,
 	rcu_read_lock();
 
 	irq = xa_load(&its->translation_cache, cache_key);
-	if (!vgic_try_get_irq_kref(irq))
+	if (!vgic_try_get_irq_ref(irq))
 		irq = NULL;
 
 	rcu_read_unlock();
@@ -571,7 +571,7 @@ static void vgic_its_cache_translation(struct kvm *kvm, struct vgic_its *its,
 	 * its_lock, as the ITE (and the reference it holds) cannot be freed.
 	 */
 	lockdep_assert_held(&its->its_lock);
-	vgic_get_irq_kref(irq);
+	vgic_get_irq_ref(irq);
 
 	old = xa_store(&its->translation_cache, cache_key, irq, GFP_KERNEL_ACCOUNT);
 

arch/arm64/kvm/vgic/vgic-v4.c

@@ -518,7 +518,7 @@ static struct vgic_irq *__vgic_host_irq_get_vlpi(struct kvm *kvm, int host_irq)
 		if (!irq->hw || irq->host_irq != host_irq)
 			continue;
 
-		if (!vgic_try_get_irq_kref(irq))
+		if (!vgic_try_get_irq_ref(irq))
 			return NULL;
 
 		return irq;

arch/arm64/kvm/vgic/vgic.c

@@ -71,7 +71,7 @@ static struct vgic_irq *vgic_get_lpi(struct kvm *kvm, u32 intid)
 	rcu_read_lock();
 
 	irq = xa_load(&dist->lpi_xa, intid);
-	if (!vgic_try_get_irq_kref(irq))
+	if (!vgic_try_get_irq_ref(irq))
 		irq = NULL;
 
 	rcu_read_unlock();
@@ -114,15 +114,6 @@ struct vgic_irq *vgic_get_vcpu_irq(struct kvm_vcpu *vcpu, u32 intid)
 	return vgic_get_irq(vcpu->kvm, intid);
 }
 
-/*
- * We can't do anything in here, because we lack the kvm pointer to
- * lock and remove the item from the lpi_list. So we keep this function
- * empty and use the return value of kref_put() to trigger the freeing.
- */
-static void vgic_irq_release(struct kref *ref)
-{
-}
-
 void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq)
 {
 	struct vgic_dist *dist = &kvm->arch.vgic;
@@ -131,7 +122,7 @@ void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq)
 	if (irq->intid < VGIC_MIN_LPI)
 		return;
 
-	if (!kref_put(&irq->refcount, vgic_irq_release))
+	if (!refcount_dec_and_test(&irq->refcount))
 		return;
 
 	xa_lock_irqsave(&dist->lpi_xa, flags);
@@ -399,7 +390,7 @@ retry:
 	 * now in the ap_list. This is safe as the caller must already hold a
 	 * reference on the irq.
 	 */
-	vgic_get_irq_kref(irq);
+	vgic_get_irq_ref(irq);
 	list_add_tail(&irq->ap_list, &vcpu->arch.vgic_cpu.ap_list_head);
 	irq->vcpu = vcpu;
 
@@ -657,7 +648,7 @@ retry:
 
 			/*
 			 * This vgic_put_irq call matches the
-			 * vgic_get_irq_kref in vgic_queue_irq_unlock,
+			 * vgic_get_irq_ref in vgic_queue_irq_unlock,
 			 * where we added the LPI to the ap_list. As
 			 * we remove the irq from the list, we drop
 			 * also drop the refcount.

arch/arm64/kvm/vgic/vgic.h

@@ -267,7 +267,7 @@ void vgic_v2_put(struct kvm_vcpu *vcpu);
 void vgic_v2_save_state(struct kvm_vcpu *vcpu);
 void vgic_v2_restore_state(struct kvm_vcpu *vcpu);
 
-static inline bool vgic_try_get_irq_kref(struct vgic_irq *irq)
+static inline bool vgic_try_get_irq_ref(struct vgic_irq *irq)
 {
 	if (!irq)
 		return false;
@@ -275,12 +275,12 @@ static inline bool vgic_try_get_irq_kref(struct vgic_irq *irq)
 	if (irq->intid < VGIC_MIN_LPI)
 		return true;
 
-	return kref_get_unless_zero(&irq->refcount);
+	return refcount_inc_not_zero(&irq->refcount);
 }
 
-static inline void vgic_get_irq_kref(struct vgic_irq *irq)
+static inline void vgic_get_irq_ref(struct vgic_irq *irq)
 {
-	WARN_ON_ONCE(!vgic_try_get_irq_kref(irq));
+	WARN_ON_ONCE(!vgic_try_get_irq_ref(irq));
 }
 
 void vgic_v3_fold_lr_state(struct kvm_vcpu *vcpu);

include/kvm/arm_vgic.h

@@ -8,8 +8,8 @@
 #include <linux/bits.h>
 #include <linux/kvm.h>
 #include <linux/irqreturn.h>
-#include <linux/kref.h>
 #include <linux/mutex.h>
+#include <linux/refcount.h>
 #include <linux/spinlock.h>
 #include <linux/static_key.h>
 #include <linux/types.h>
@@ -142,7 +142,7 @@ struct vgic_irq {
 	bool active;
 	bool enabled;
 	bool hw;			/* Tied to HW IRQ */
-	struct kref refcount;		/* Used for LPIs */
+	refcount_t refcount;		/* Used for LPIs */
 	u32 hwintid;			/* HW INTID number */
 	unsigned int host_irq;		/* linux irq corresponding to hwintid */
 	union {