[PATCH v5 08/19] arm/arm64: KVM: make the maximum number of vCPUs a per-VM value

[marc.zyngier@arm.com (Marc Zyngier)]

On Mon, Dec 08 2014 at 12:37:43 PM, Andre Przywara <andre.przywara@arm.com> 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 <andre.przywara@arm.com>
> ---
> Changelog v4...v5:
> - add define for GIC_V2_MAX_CPUS
> - rename max_hw_vcpus
> - add prototype for ARM non-VGIC configs
>
> Changelog v3...v4:
> - initialize max_vcpus with limit based on host GIC
> - remove *_init_emul_* from VGIC backend
> - refine VCPU limit on VGIC creation
> - print warning when userland tries to create more VCPUs than supported
>
>  arch/arm/include/asm/kvm_host.h   |    1 +
>  arch/arm/kvm/arm.c                |    8 ++++++++
>  arch/arm64/include/asm/kvm_host.h |    3 +++
>  include/kvm/arm_vgic.h            |    8 ++++++++
>  virt/kvm/arm/vgic-v2.c            |    1 +
>  virt/kvm/arm/vgic-v3.c            |    1 +
>  virt/kvm/arm/vgic.c               |   22 ++++++++++++++++++++++
>  7 files changed, 44 insertions(+)
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index b443dfe..7969e6e 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -68,6 +68,7 @@ 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 8817fbd..c3d0fbd 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -132,6 +132,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>  	/* 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);
> @@ -213,6 +216,11 @@ 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 286bb61..f9e130d 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -59,6 +59,9 @@ 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/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index e691932..72a9fef 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -33,6 +33,7 @@
>  #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)
> @@ -132,6 +133,7 @@ struct vgic_params {
>  	unsigned int	maint_irq;
>  	/* Virtual control interface base address */
>  	void __iomem	*vctrl_base;
> +	int		max_gic_vcpus;
>  };
>  
>  struct vgic_vm_ops {
> @@ -288,6 +290,7 @@ struct kvm_exit_mmio;
>  #ifdef CONFIG_KVM_ARM_VGIC
>  int kvm_vgic_addr(struct kvm *kvm, unsigned long type, u64 *addr, bool write);
>  int kvm_vgic_hyp_init(void);
> +int kvm_vgic_get_max_vcpus(void);
>  int kvm_vgic_init(struct kvm *kvm);
>  int kvm_vgic_create(struct kvm *kvm, u32 type);
>  void kvm_vgic_destroy(struct kvm *kvm);
> @@ -387,6 +390,11 @@ static inline bool vgic_initialized(struct kvm *kvm)
>  {
>  	return true;
>  }
> +
> +static inline int kvm_vgic_get_max_vcpus(void)
> +{
> +	return KVM_MAX_VCPUS;
> +}
>  #endif
>  
>  #endif
> diff --git a/virt/kvm/arm/vgic-v2.c b/virt/kvm/arm/vgic-v2.c
> index e1cd3cb..e8b82b2 100644
> --- a/virt/kvm/arm/vgic-v2.c
> +++ b/virt/kvm/arm/vgic-v2.c
> @@ -237,6 +237,7 @@ int vgic_v2_probe(struct device_node *vgic_node,
>  		 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;
> diff --git a/virt/kvm/arm/vgic-v3.c b/virt/kvm/arm/vgic-v3.c
> index d14c75f..ea39bad 100644
> --- a/virt/kvm/arm/vgic-v3.c
> +++ b/virt/kvm/arm/vgic-v3.c
> @@ -235,6 +235,7 @@ int vgic_v3_probe(struct device_node *vgic_node,
>  	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);
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index c481362..dcdbae5 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -1848,6 +1848,17 @@ static int vgic_vcpu_init_maps(struct kvm_vcpu *vcpu, int nr_irqs)
>  }
>  
>  /**
> + * 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;
> +}
> +
> +/**
>   * kvm_vgic_vcpu_init - Initialize per-vcpu VGIC state
>   * @vcpu: pointer to the vcpu struct
>   *
> @@ -2069,6 +2080,8 @@ static int vgic_v2_init_emulation(struct kvm *kvm)
>  	dist->vm_ops.vgic_init = vgic_v2_init;
>  	dist->vm_ops.vgic_init_maps = vgic_v2_init_maps;
>  
> +	kvm->arch.max_vcpus = VGIC_V2_MAX_CPUS;
> +
>  	return 0;
>  }
>  
> @@ -2085,6 +2098,15 @@ static int init_vgic_model(struct kvm *kvm, int type)
>  		break;
>  	}
>  
> +	if (ret)
> +		return ret;
> +
> +	if (atomic_read(&kvm->online_vcpus) > kvm->arch.max_vcpus) {
> +		pr_warn_ratelimited("VGIC model only supports up to %d vCPUs\n",
> +			kvm->arch.max_vcpus);

I'm not overly keen on the kernel spitting out messages based on
userspace errors. Returning an error should be enough.

> +		ret = -EINVAL;
> +	}
> +
>  	return ret;
>  }

I'm also slightly confused as to how it works when I create a VM without
an in-kernel GIC. How many vcpus am I allowed?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny.