| Message ID | 20211116163443.88707-2-vkuznets@redhat.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | KVM: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS and re-purpose it on x86 | expand |
On Tue, 16 Nov 2021 16:34:38 +0000, Vitaly Kuznetsov <vkuznets@redhat.com> wrote: > > Generally, it doesn't make sense to return the recommended maximum number > of vCPUs which exceeds the maximum possible number of vCPUs. > > Note: ARM64 is special as the value returned by KVM_CAP_MAX_VCPUS differs > depending on whether it is a system-wide ioctl or a per-VM one. Previously, > KVM_CAP_NR_VCPUS didn't have this difference and it seems preferable to > keep the status quo. Cap KVM_CAP_NR_VCPUS by kvm_arm_default_max_vcpus() > which is what gets returned by system-wide KVM_CAP_MAX_VCPUS. > > Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Acked-by: Marc Zyngier <maz@kernel.org> M.
On 11/16/21 17:34, Vitaly Kuznetsov wrote: > - r = num_online_cpus(); > + /* > + * ARM64 treats KVM_CAP_NR_CPUS differently from all other > + * architectures, as it does not always bound it to > + * num_online_cpus(). It should not matter much because this ^^^^^^^^^^^^^^^^^^ KVM_CAP_MAX_VCPUS (sorry for the typo in my suggestion). I'll fix it when applying. Paolo > + * is just an advisory value. > + */ > + r = min_t(unsigned int, num_online_cpus(), > + kvm_arm_default_max_vcpus());
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 7838e9fb693e..0690c76def5d 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -223,7 +223,14 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) r = 1; break; case KVM_CAP_NR_VCPUS: - r = num_online_cpus(); + /* + * ARM64 treats KVM_CAP_NR_CPUS differently from all other + * architectures, as it does not always bound it to + * num_online_cpus(). It should not matter much because this + * is just an advisory value. + */ + 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:
Generally, it doesn't make sense to return the recommended maximum number of vCPUs which exceeds the maximum possible number of vCPUs. Note: ARM64 is special as the value returned by KVM_CAP_MAX_VCPUS differs depending on whether it is a system-wide ioctl or a per-VM one. Previously, KVM_CAP_NR_VCPUS didn't have this difference and it seems preferable to keep the status quo. Cap KVM_CAP_NR_VCPUS by kvm_arm_default_max_vcpus() which is what gets returned by system-wide KVM_CAP_MAX_VCPUS. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> --- arch/arm64/kvm/arm.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)