arm/arm64: KVM: make the maximum number of vCPUs a per-VM value

Currently the maximum number of vCPUs supported is a global value
limited by the used GIC model. GICv3 will lift this limit, but we
still need to observe it for guests using GICv2.
So the maximum number of vCPUs is per-VM value, depending on the
GIC model the guest uses.
Store and check the value in struct kvm_arch, but keep it down to
8 for now.

Signed-off-by: Andre Przywara <[e-mail]>
Signed-off-by: Christoffer Dall <[e-mail]>

arch/arm/include/asm/kvm_host.h

···
 
 	/* Interrupt controller */
 	struct vgic_dist	vgic;
+	int max_vcpus;
 };
 
 #define KVM_NR_MEM_OBJS     40

arch/arm/kvm/arm.c

···
 	/* Mark the initial VMID generation invalid */
 	kvm->arch.vmid_gen = 0;
 
+	/* The maximum number of VCPUs is limited by the host's GIC model */
+	kvm->arch.max_vcpus = kvm_vgic_get_max_vcpus();
+
 	return ret;
 out_free_stage2_pgd:
 	kvm_free_stage2_pgd(kvm);
···
 
 	if (irqchip_in_kernel(kvm) && vgic_initialized(kvm)) {
 		err = -EBUSY;
+		goto out;
+	}
+
+	if (id >= kvm->arch.max_vcpus) {
+		err = -EINVAL;
 		goto out;
 	}
 

arch/arm64/include/asm/kvm_host.h

···
 	/* VTTBR value associated with above pgd and vmid */
 	u64    vttbr;
 
+	/* The maximum number of vCPUs depends on the used GIC model */
+	int max_vcpus;
+
 	/* Interrupt controller */
 	struct vgic_dist	vgic;
 

include/kvm/arm_vgic.h

···
 #define VGIC_V2_MAX_LRS		(1 << 6)
 #define VGIC_V3_MAX_LRS		16
 #define VGIC_MAX_IRQS		1024
+#define VGIC_V2_MAX_CPUS	8
 
 /* Sanity checks... */
 #if (KVM_MAX_VCPUS > 8)
···
 	unsigned int	maint_irq;
 	/* Virtual control interface base address */
 	void __iomem	*vctrl_base;
+	int		max_gic_vcpus;
 };
 
 struct vgic_vm_ops {
···
 int kvm_vgic_addr(struct kvm *kvm, unsigned long type, u64 *addr, bool write);
 int kvm_vgic_hyp_init(void);
 int kvm_vgic_map_resources(struct kvm *kvm);
+int kvm_vgic_get_max_vcpus(void);
 int kvm_vgic_create(struct kvm *kvm, u32 type);
 void kvm_vgic_destroy(struct kvm *kvm);
 void kvm_vgic_vcpu_destroy(struct kvm_vcpu *vcpu);
···
 static inline bool vgic_ready(struct kvm *kvm)
 {
 	return true;
+}
+
+static inline int kvm_vgic_get_max_vcpus(void)
+{
+	return KVM_MAX_VCPUS;
 }
 #endif
 

virt/kvm/arm/vgic-v2.c

···
 		 vctrl_res.start, vgic->maint_irq);
 
 	vgic->type = VGIC_V2;
+	vgic->max_gic_vcpus = VGIC_V2_MAX_CPUS;
 	*ops = &vgic_v2_ops;
 	*params = vgic;
 	goto out;

virt/kvm/arm/vgic-v3.c

···
 	vgic->vcpu_base = vcpu_res.start;
 	vgic->vctrl_base = NULL;
 	vgic->type = VGIC_V3;
+	vgic->max_gic_vcpus = KVM_MAX_VCPUS;
 
 	kvm_info("%s@%llx IRQ%d\n", vgic_node->name,
 		 vcpu_res.start, vgic->maint_irq);

virt/kvm/arm/vgic.c

···
 	return 0;
 }
 
+/**
+ * kvm_vgic_get_max_vcpus - Get the maximum number of VCPUs allowed by HW
+ *
+ * The host's GIC naturally limits the maximum amount of VCPUs a guest
+ * can use.
+ */
+int kvm_vgic_get_max_vcpus(void)
+{
+	return vgic->max_gic_vcpus;
+}
+
 void kvm_vgic_destroy(struct kvm *kvm)
 {
 	struct vgic_dist *dist = &kvm->arch.vgic;
···
 	dist->vm_ops.add_sgi_source = vgic_v2_add_sgi_source;
 	dist->vm_ops.init_model = vgic_v2_init_model;
 	dist->vm_ops.map_resources = vgic_v2_map_resources;
+
+	kvm->arch.max_vcpus = VGIC_V2_MAX_CPUS;
 }
 
 static int init_vgic_model(struct kvm *kvm, int type)
···
 	default:
 		return -ENODEV;
 	}
+
+	if (atomic_read(&kvm->online_vcpus) > kvm->arch.max_vcpus)
+		return -E2BIG;
 
 	return 0;
 }