arm/arm64: KVM: vgic: delay vgic allocation until init time

It is now quite easy to delay the allocation of the vgic tables
until we actually require it to be up and running (when the first
vcpu is kicking around, or someones tries to access the GIC registers).

This allow us to allocate memory for the exact number of CPUs we
have. As nobody configures the number of interrupts just yet,
use a fallback to VGIC_NR_IRQS_LEGACY.

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm/kvm/arm.c

@@ -261,16 +261,9 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
 
 int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 {
-	int ret;
-
 	/* Force users to call KVM_ARM_VCPU_INIT */
 	vcpu->arch.target = -1;
 
-	/* Set up VGIC */
-	ret = kvm_vgic_vcpu_init(vcpu);
-	if (ret)
-		return ret;
-
 	/* Set up the timer */
 	kvm_timer_vcpu_init(vcpu);
 

include/kvm/arm_vgic.h

@@ -277,7 +277,6 @@ int kvm_vgic_hyp_init(void);
 int kvm_vgic_init(struct kvm *kvm);
 int kvm_vgic_create(struct kvm *kvm);
 void kvm_vgic_destroy(struct kvm *kvm);
-int kvm_vgic_vcpu_init(struct kvm_vcpu *vcpu);
 void kvm_vgic_vcpu_destroy(struct kvm_vcpu *vcpu);
 void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu);
 void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu);

virt/kvm/arm/vgic.c

@@ -1729,15 +1729,12 @@ static int vgic_vcpu_init_maps(struct kvm_vcpu *vcpu, int nr_irqs)
  * Initialize the vgic_cpu struct and vgic_dist struct fields pertaining to
  * this vcpu and enable the VGIC for this VCPU
  */
-int kvm_vgic_vcpu_init(struct kvm_vcpu *vcpu)
+static void 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 i;
 
-	if (vcpu->vcpu_id >= dist->nr_cpus)
-		return -EBUSY;
-
 	for (i = 0; i < dist->nr_irqs; i++) {
 		if (i < VGIC_NR_PPIS)
 			vgic_bitmap_set_irq_val(&dist->irq_enabled,
@@ -1757,8 +1754,6 @@ int kvm_vgic_vcpu_init(struct kvm_vcpu *vcpu)
 	vgic_cpu->nr_lr = vgic->nr_lr;
 
 	vgic_enable(vcpu);
-
-	return 0;
 }
 
 void kvm_vgic_destroy(struct kvm *kvm)
@@ -1802,8 +1797,17 @@ static int vgic_init_maps(struct kvm *kvm)
 	int nr_cpus, nr_irqs;
 	int ret, i;
 
-	nr_cpus = dist->nr_cpus = KVM_MAX_VCPUS;
+	if (dist->nr_cpus)	/* Already allocated */
+		return 0;
+
+	nr_cpus = dist->nr_cpus = atomic_read(&kvm->online_vcpus);
+	if (!nr_cpus)		/* No vcpus? Can't be good... */
+		return -EINVAL;
 
+	/*
+	 * If nobody configured the number of interrupts, use the
+	 * legacy one.
+	 */
 	if (!dist->nr_irqs)
 		dist->nr_irqs = VGIC_NR_IRQS_LEGACY;
 
@@ -1849,6 +1853,9 @@ static int vgic_init_maps(struct kvm *kvm)
 		}
 	}
 
+	for (i = VGIC_NR_PRIVATE_IRQS; i < dist->nr_irqs; i += 4)
+		vgic_set_target_reg(kvm, 0, i);
+
 out:
 	if (ret)
 		kvm_vgic_destroy(kvm);
@@ -1867,6 +1874,7 @@ out:
  */
 int kvm_vgic_init(struct kvm *kvm)
 {
+	struct kvm_vcpu *vcpu;
 	int ret = 0, i;
 
 	if (!irqchip_in_kernel(kvm))
@@ -1884,6 +1892,12 @@ int kvm_vgic_init(struct kvm *kvm)
 		goto out;
 	}
 
+	ret = vgic_init_maps(kvm);
+	if (ret) {
+		kvm_err("Unable to allocate maps\n");
+		goto out;
+	}
+
 	ret = kvm_phys_addr_ioremap(kvm, kvm->arch.vgic.vgic_cpu_base,
 				    vgic->vcpu_base, KVM_VGIC_V2_CPU_SIZE);
 	if (ret) {
@@ -1891,11 +1905,13 @@ int kvm_vgic_init(struct kvm *kvm)
 		goto out;
 	}
 
-	for (i = VGIC_NR_PRIVATE_IRQS; i < kvm->arch.vgic.nr_irqs; i += 4)
-		vgic_set_target_reg(kvm, 0, i);
+	kvm_for_each_vcpu(i, vcpu, kvm)
+		kvm_vgic_vcpu_init(vcpu);
 
 	kvm->arch.vgic.ready = true;
 out:
+	if (ret)
+		kvm_vgic_destroy(kvm);
 	mutex_unlock(&kvm->lock);
 	return ret;
 }
@@ -1936,10 +1952,6 @@ int kvm_vgic_create(struct kvm *kvm)
 	kvm->arch.vgic.vgic_dist_base = VGIC_ADDR_UNDEF;
 	kvm->arch.vgic.vgic_cpu_base = VGIC_ADDR_UNDEF;
 
-	ret = vgic_init_maps(kvm);
-	if (ret)
-		kvm_err("Unable to allocate maps\n");
-
 out_unlock:
 	for (; vcpu_lock_idx >= 0; vcpu_lock_idx--) {
 		vcpu = kvm_get_vcpu(kvm, vcpu_lock_idx);
@@ -2140,6 +2152,10 @@ static int vgic_attr_regs_access(struct kvm_device *dev,
 
 	mutex_lock(&dev->kvm->lock);
 
+	ret = vgic_init_maps(dev->kvm);
+	if (ret)
+		goto out;
+
 	if (cpuid >= atomic_read(&dev->kvm->online_vcpus)) {
 		ret = -EINVAL;
 		goto out;