[PATCH v3 07/10] limit number of VCPUs on demand

[Marc Zyngier]

On 17/06/15 12:21, Andre Przywara wrote:
> Currently the ARM GIC checks the number of VCPUs against a fixed
> limit, which is GICv2 specific. Don't pretend we know better than the
> kernel and let's get rid of that explicit check.
> Instead be more relaxed about KVM_CREATE_VCPU failing with EINVAL,
> which is the way the kernel communicates having reached a VCPU limit.
> If we see this and have at least brought up one VCPU already
> successfully, then don't panic, but limit the number of VCPUs instead.
> 
> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
> ---
>  arm/gic.c     |  6 ------
>  arm/kvm-cpu.c | 11 +++++++++--
>  kvm-cpu.c     |  7 +++++++
>  3 files changed, 16 insertions(+), 8 deletions(-)
> 
> diff --git a/arm/gic.c b/arm/gic.c
> index 99f0d2b..05f85a2 100644
> --- a/arm/gic.c
> +++ b/arm/gic.c
> @@ -84,12 +84,6 @@ int gic__create(struct kvm *kvm)
>  {
>  	int err;
>  
> -	if (kvm->nrcpus > GIC_MAX_CPUS) {
> -		pr_warning("%d CPUS greater than maximum of %d -- truncating\n",
> -				kvm->nrcpus, GIC_MAX_CPUS);
> -		kvm->nrcpus = GIC_MAX_CPUS;
> -	}
> -
>  	/* Try the new way first, and fallback on legacy method otherwise */
>  	err = gic__create_device(kvm);
>  	if (err)
> diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c
> index 7780251..c1cf51d 100644
> --- a/arm/kvm-cpu.c
> +++ b/arm/kvm-cpu.c
> @@ -47,12 +47,19 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
>  	};
>  
>  	vcpu = calloc(1, sizeof(struct kvm_cpu));
> -	if (!vcpu)
> +	if (!vcpu) {
> +		errno = ENOMEM;
>  		return NULL;
> +	}

Isn't errno already set when calloc fails?

>  
>  	vcpu->vcpu_fd = ioctl(kvm->vm_fd, KVM_CREATE_VCPU, cpu_id);
> -	if (vcpu->vcpu_fd < 0)
> +	if (vcpu->vcpu_fd < 0) {
> +		if (errno == EINVAL) {
> +			free(vcpu);
> +			return NULL;
> +		}
>  		die_perror("KVM_CREATE_VCPU ioctl");
> +	}
>  
>  	mmap_size = ioctl(kvm->sys_fd, KVM_GET_VCPU_MMAP_SIZE, 0);
>  	if (mmap_size < 0)
> diff --git a/kvm-cpu.c b/kvm-cpu.c
> index 5d90664..7a9d689 100644
> --- a/kvm-cpu.c
> +++ b/kvm-cpu.c
> @@ -222,11 +222,18 @@ int kvm_cpu__init(struct kvm *kvm)
>  	for (i = 0; i < kvm->nrcpus; i++) {
>  		kvm->cpus[i] = kvm_cpu__arch_init(kvm, i);
>  		if (!kvm->cpus[i]) {
> +			if (i > 0 && errno == EINVAL)
> +				break;
>  			pr_warning("unable to initialize KVM VCPU");
>  			goto fail_alloc;
>  		}
>  	}
>  
> +	if (i < kvm->nrcpus) {
> +		kvm->nrcpus = i;
> +		printf("  # The kernel limits the number of CPUs to %d\n", i);
> +	}
> +
>  	return 0;
>  
>  fail_alloc:
> 

Thanks,

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