KVM_CAP_MAX_VCPUS always return the maximum possible number of VCPUs, irrespective of the selected interrupt controller. This is pretty misleading for userspace that selects a GICv2 on a GICv3 system that supports v2 compat: It always gets a maximum of 512 VCPUs, even if the effective limit is 8. The 9th VCPU will fail to be created, which is unexpected as far as userspace is concerned. Fortunately, we already have the right information stashed in the kvm structure, and we can return it as requested. Reported-by: Ard Biesheuvel <ardb@xxxxxxxxxx> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx> Tested-by: Alexandru Elisei <alexandru.elisei@xxxxxxx> Reviewed-by: Alexandru Elisei <alexandru.elisei@xxxxxxx> Link: https://lore.kernel.org/r/20200427141507.284985-1-maz@xxxxxxxxxx --- arch/arm64/kvm/arm.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 0ea9a0266d9a..e01d44df98df 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -95,6 +95,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, return r; } +static int kvm_arm_default_max_vcpus(void) +{ + return vgic_present ? kvm_vgic_get_max_vcpus() : KVM_MAX_VCPUS; +} + /** * kvm_arch_init_vm - initializes a VM data structure * @kvm: pointer to the KVM struct @@ -128,8 +133,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) kvm->arch.vmid.vmid_gen = 0; /* The maximum number of VCPUs is limited by the host's GIC model */ - kvm->arch.max_vcpus = vgic_present ? - kvm_vgic_get_max_vcpus() : KVM_MAX_VCPUS; + kvm->arch.max_vcpus = kvm_arm_default_max_vcpus(); return ret; out_free_stage2_pgd: @@ -204,10 +208,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) r = num_online_cpus(); break; case KVM_CAP_MAX_VCPUS: - r = KVM_MAX_VCPUS; - break; case KVM_CAP_MAX_VCPU_ID: - r = KVM_MAX_VCPU_ID; + if (kvm) + r = kvm->arch.max_vcpus; + else + r = kvm_arm_default_max_vcpus(); break; case KVM_CAP_MSI_DEVID: if (!kvm) -- 2.26.2
