Subject: [PATCH v2 06/15] arm/arm64: KVM: make the maximum number of vCPUs a per-VM value

From: [email-masked] (Christoffer Dall)
Date: Wed, 15 Oct 2014 09:27:34 -0700

On Thu, Aug 21, 2014 at 02:06:47PM +0100, Andre Przywara wrote:
> 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 <[email-masked]>
> ---
>  arch/arm/include/asm/kvm_host.h   |    1 +
>  arch/arm/kvm/arm.c                |    6 ++++++
>  arch/arm64/include/asm/kvm_host.h |    3 +++
>  virt/kvm/arm/vgic-v2.c            |    5 +++++
>  virt/kvm/arm/vgic-v3.c            |    6 ++++++
>  5 files changed, 21 insertions(+)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index cf99ad0..0638419 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -67,6 +67,7 @@ struct kvm_arch {
>  
>  	/* Interrupt controller */
>  	struct vgic_dist	vgic;
> +	int max_vcpus;
>  };
>  
>  #define KVM_NR_MEM_OBJS     40
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 157e1b6..190f05f 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -142,6 +142,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>  
>  	/* Mark the initial VMID generation invalid */
>  	kvm->arch.vmid_gen = 0;
> +	kvm->arch.max_vcpus = CONFIG_KVM_ARM_MAX_VCPUS;
>  
>  	return ret;
>  out_free_stage2_pgd:
> @@ -223,6 +224,11 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id)
>  	int err;
>  	struct kvm_vcpu *vcpu;
>  
> +	if (id >= kvm->arch.max_vcpus) {
> +		err = -EINVAL;
> +		goto out;
> +	}
> +
>  	vcpu = kmem_cache_zalloc(kvm_vcpu_cache, GFP_KERNEL);
>  	if (!vcpu) {
>  		err = -ENOMEM;
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 017fbae..a325161 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -58,6 +58,9 @@ struct kvm_arch {
>  	/* 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;
>  
> diff --git a/virt/kvm/arm/vgic-v2.c b/virt/kvm/arm/vgic-v2.c
> index 90947c6..c7362ff 100644
> --- a/virt/kvm/arm/vgic-v2.c
> +++ b/virt/kvm/arm/vgic-v2.c
> @@ -177,11 +177,16 @@ static struct vgic_params vgic_v2_params;
>  static bool vgic_v2_init_emul(struct kvm *kvm, int type)
>  {
>  	struct vgic_vm_ops *vm_ops = &kvm->arch.vgic.vm_ops;
> +	int nr_vcpus;
>  
>  	switch (type) {
>  	case KVM_DEV_TYPE_ARM_VGIC_V2:
> +		nr_vcpus = atomic_read(&kvm->online_vcpus);
> +		if (nr_vcpus > 8)
> +			return false;
>  		vm_ops->get_lr = vgic_v2_get_lr;
>  		vm_ops->set_lr = vgic_v2_set_lr;
> +		kvm->arch.max_vcpus = 8;
>  		return true;
>  	}
>  
> diff --git a/virt/kvm/arm/vgic-v3.c b/virt/kvm/arm/vgic-v3.c
> index a38339e..86e8b99 100644
> --- a/virt/kvm/arm/vgic-v3.c
> +++ b/virt/kvm/arm/vgic-v3.c
> @@ -171,11 +171,17 @@ static const struct vgic_ops vgic_v3_ops = {
>  static bool vgic_v3_init_emul_compat(struct kvm *kvm, int type)
>  {
>  	struct vgic_vm_ops *vm_ops = &kvm->arch.vgic.vm_ops;
> +	int nr_vcpus;
>  
>  	switch (type) {
>  	case KVM_DEV_TYPE_ARM_VGIC_V2:
> +		nr_vcpus = atomic_read(&kvm->online_vcpus);
> +		if (nr_vcpus > 8)
> +			return false;
> +

I have a feeling we could be seeing this error a bit, could we dedicate
an error code for the purpose or print a ratelimited warning or
something?

>  		vm_ops->get_lr = vgic_v3_get_lr;
>  		vm_ops->set_lr = vgic_v3_set_lr;
> +		kvm->arch.max_vcpus = 8;
>  		return true;
>  	}
>  	return false;
> -- 
> 1.7.9.5
> 
Thanks,
-Christoffer