Hi,
On 4/27/20 3:17 PM, Marc Zyngier wrote:
> On arm64, the maximum number of vcpus is constrained by the type
> of interrupt controller that has been selected (GICv2 imposes a
> limit of 8 vcpus, while GICv3 currently has a limit of 512).
>
> It is thus important to request this limit on the VM file descriptor
> rather than on the one that corresponds to /dev/kvm, as the latter
> is likely to return something that doesn't take the constraints into
> account.
>
> Reported-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> kvm.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kvm.c b/kvm.c
> index e327541..3d5173d 100644
> --- a/kvm.c
> +++ b/kvm.c
> @@ -406,7 +406,7 @@ int kvm__recommended_cpus(struct kvm *kvm)
> {
> int ret;
>
> - ret = ioctl(kvm->sys_fd, KVM_CHECK_EXTENSION, KVM_CAP_NR_VCPUS);
> + ret = ioctl(kvm->vm_fd, KVM_CHECK_EXTENSION, KVM_CAP_NR_VCPUS);
> if (ret <= 0)
> /*
> * api.txt states that if KVM_CAP_NR_VCPUS does not exist,
> @@ -421,7 +421,7 @@ int kvm__max_cpus(struct kvm *kvm)
> {
> int ret;
>
> - ret = ioctl(kvm->sys_fd, KVM_CHECK_EXTENSION, KVM_CAP_MAX_VCPUS);
> + ret = ioctl(kvm->vm_fd, KVM_CHECK_EXTENSION, KVM_CAP_MAX_VCPUS);
> if (ret <= 0)
> ret = kvm__recommended_cpus(kvm);
>
I've checked that gic__create comes before the call kvm__recommended_capus:
gic__create is in core_init (called via kvm__init->kvm_arch_init), and
kvm__recommended_cpus is in base_init (called via kvm__cpu_init ->
kvm__{recommended,max}_cpus).
The KVM api documentation states that KVM_CHECK_EXTENSION is available for the vm
fd only if the system capability KVM_CAP_CHECK_EXTENSION_VM is present. kvmtool
already has a function for checking extensions on the vm fd, it's called
kvm__supports_vm_extension. Can we use that instead of doing the ioctl directly on
the vm fd?
Thanks,
Alex
