KVM: arm64: vgic: Allocate private interrupts on demand

Private interrupts are currently part of the CPU interface structure
that is part of each and every vcpu we create.

Currently, we have 32 of them per vcpu, resulting in a per-vcpu array
that is just shy of 4kB. On its own, that's no big deal, but it gets
in the way of other things:

- each vcpu gets mapped at EL2 on nVHE/hVHE configurations. This
  requires memory that is physically contiguous. However, the EL2
  code has no purpose looking at the interrupt structures and
  could do without them being mapped.

- supporting features such as EPPIs, which extend the number of
  private interrupts past the 32 limit would make the array
  even larger, even for VMs that do not use the EPPI feature.

Address these issues by moving the private interrupt array outside
of the vcpu, and replace it with a simple pointer. We take this
opportunity to make it obvious what gets initialised when, as
that path was remarkably opaque, and tighten the locking.

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240502154545.3012089-1-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

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

@@ -182,27 +182,22 @@ static int kvm_vgic_dist_init(struct kvm *kvm, unsigned int nr_spis)
 	return 0;
 }
 
-/**
- * kvm_vgic_vcpu_init() - Initialize static VGIC VCPU data
- * structures and register VCPU-specific KVM iodevs
- *
- * @vcpu: pointer to the VCPU being created and initialized
- *
- * Only do initialization, but do not actually enable the
- * VGIC CPU interface
- */
-int kvm_vgic_vcpu_init(struct kvm_vcpu *vcpu)
+static int vgic_allocate_private_irqs_locked(struct kvm_vcpu *vcpu)
 {
 	struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
-	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
-	int ret = 0;
 	int i;
 
-	vgic_cpu->rd_iodev.base_addr = VGIC_ADDR_UNDEF;
+	lockdep_assert_held(&vcpu->kvm->arch.config_lock);
 
-	INIT_LIST_HEAD(&vgic_cpu->ap_list_head);
-	raw_spin_lock_init(&vgic_cpu->ap_list_lock);
-	atomic_set(&vgic_cpu->vgic_v3.its_vpe.vlpi_count, 0);
+	if (vgic_cpu->private_irqs)
+		return 0;
+
+	vgic_cpu->private_irqs = kcalloc(VGIC_NR_PRIVATE_IRQS,
+					 sizeof(struct vgic_irq),
+					 GFP_KERNEL_ACCOUNT);
+
+	if (!vgic_cpu->private_irqs)
+		return -ENOMEM;
 
 	/*
 	 * Enable and configure all SGIs to be edge-triggered and
@@ -227,9 +222,48 @@ int kvm_vgic_vcpu_init(struct kvm_vcpu *vcpu)
 		}
 	}
 
+	return 0;
+}
+
+static int vgic_allocate_private_irqs(struct kvm_vcpu *vcpu)
+{
+	int ret;
+
+	mutex_lock(&vcpu->kvm->arch.config_lock);
+	ret = vgic_allocate_private_irqs_locked(vcpu);
+	mutex_unlock(&vcpu->kvm->arch.config_lock);
+
+	return ret;
+}
+
+/**
+ * kvm_vgic_vcpu_init() - Initialize static VGIC VCPU data
+ * structures and register VCPU-specific KVM iodevs
+ *
+ * @vcpu: pointer to the VCPU being created and initialized
+ *
+ * Only do initialization, but do not actually enable the
+ * VGIC CPU interface
+ */
+int kvm_vgic_vcpu_init(struct kvm_vcpu *vcpu)
+{
+	struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
+	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
+	int ret = 0;
+
+	vgic_cpu->rd_iodev.base_addr = VGIC_ADDR_UNDEF;
+
+	INIT_LIST_HEAD(&vgic_cpu->ap_list_head);
+	raw_spin_lock_init(&vgic_cpu->ap_list_lock);
+	atomic_set(&vgic_cpu->vgic_v3.its_vpe.vlpi_count, 0);
+
 	if (!irqchip_in_kernel(vcpu->kvm))
 		return 0;
 
+	ret = vgic_allocate_private_irqs(vcpu);
+	if (ret)
+		return ret;
+
 	/*
 	 * If we are creating a VCPU with a GICv3 we must also register the
 	 * KVM io device for the redistributor that belongs to this VCPU.
@@ -285,10 +319,13 @@ int vgic_init(struct kvm *kvm)
 
 	/* Initialize groups on CPUs created before the VGIC type was known */
 	kvm_for_each_vcpu(idx, vcpu, kvm) {
-		struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
+		ret = vgic_allocate_private_irqs_locked(vcpu);
+		if (ret)
+			goto out;
 
 		for (i = 0; i < VGIC_NR_PRIVATE_IRQS; i++) {
-			struct vgic_irq *irq = &vgic_cpu->private_irqs[i];
+			struct vgic_irq *irq = vgic_get_irq(kvm, vcpu, i);
+
 			switch (dist->vgic_model) {
 			case KVM_DEV_TYPE_ARM_VGIC_V3:
 				irq->group = 1;
@@ -300,8 +337,12 @@ int vgic_init(struct kvm *kvm)
 				break;
 			default:
 				ret = -EINVAL;
-				goto out;
 			}
+
+			vgic_put_irq(kvm, irq);
+
+			if (ret)
+				goto out;
 		}
 	}
 
@@ -381,6 +422,9 @@ static void __kvm_vgic_vcpu_destroy(struct kvm_vcpu *vcpu)
 	vgic_flush_pending_lpis(vcpu);
 
 	INIT_LIST_HEAD(&vgic_cpu->ap_list_head);
+	kfree(vgic_cpu->private_irqs);
+	vgic_cpu->private_irqs = NULL;
+
 	if (vcpu->kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3) {
 		vgic_unregister_redist_iodev(vcpu);
 		vgic_cpu->rd_iodev.base_addr = VGIC_ADDR_UNDEF;

include/kvm/arm_vgic.h

@@ -330,7 +330,7 @@ struct vgic_cpu {
 		struct vgic_v3_cpu_if	vgic_v3;
 	};
 
-	struct vgic_irq private_irqs[VGIC_NR_PRIVATE_IRQS];
+	struct vgic_irq *private_irqs;
 
 	raw_spinlock_t ap_list_lock;	/* Protects the ap_list */