Messages in this thread | | | Date | Thu, 11 Nov 2021 19:36:34 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH 1/5] KVM: arm64: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS |
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Hi Vitaly,
On 2021-11-11 16:27, Vitaly Kuznetsov wrote: > It doesn't make sense to return the recommended maximum number of > vCPUs which exceeds the maximum possible number of vCPUs. > > Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> > --- > arch/arm64/kvm/arm.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index 7838e9fb693e..391dc7a921d5 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -223,7 +223,12 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, > long ext) > r = 1; > break; > case KVM_CAP_NR_VCPUS: > - r = num_online_cpus(); > + if (kvm) > + r = min_t(unsigned int, num_online_cpus(), > + kvm->arch.max_vcpus); > + else > + r = min_t(unsigned int, num_online_cpus(), > + kvm_arm_default_max_vcpus()); > break; > case KVM_CAP_MAX_VCPUS: > case KVM_CAP_MAX_VCPU_ID:
This looks odd. This means that depending on the phase userspace is in while initialising the VM, KVM_CAP_NR_VCPUS can return one thing or the other.
For example, I create a VM on a 32 CPU system, NR_VCPUS says 32. I create a GICv2 interrupt controller, it now says 8.
That's a change in behaviour that is visible by userspace, which I'm keen on avoiding. I'd rather have the kvm and !kvm cases return the same thing.
Thanks,
M. -- Jazz is not dead. It just smells funny...
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