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

[Andre Przywara <andre.przywara@arm.com>]

On 15/10/14 17:27, Christoffer Dall wrote:
> 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 <andre.przywara@arm.com>
>> ---
>>  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?

Did the latter. To be found in an inbox near you very soon.

Cheers,
Andre.

> 
>>  		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
>