Re: [PATCH 1/5] KVM: arm64: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS
From: Marc Zyngier <maz@kernel.org>
Date: 2021-11-11 19:36:40
Also in:
kvm, kvm-riscv, linux-arm-kernel, lkml
Hi Vitaly, On 2021-11-11 16:27, Vitaly Kuznetsov wrote:
quoted hunk ↗ jump to hunk
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...