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

From: [email-masked] (Andre Przywara)
Date: Mon, 05 Jan 2015 17:34:02 +0000

Hi Marc,

On 23/12/14 12:07, Marc Zyngier wrote:
> On Mon, Dec 08 2014 at 12:37:43 PM, Andre Przywara <[email-masked]> 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]>
>> ---
>> 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.

I added this message after a comment from Christoffer:
On 15/10/14 17:27, Christoffer Dall wrote:
>>  	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?

Christoffer, can you state whether it's OK to do away with the warning
message and just use the -EINVAL?

> 
>> +		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?

Mmmh, fair point. I guess we should just allow KVM_MAX_VCPUS in this
case, right? Has anyone tested userland GIC emulation recently?
I will see if I find some method of testing this with QEMU.

Cheers,
Andre.