Christian Borntraeger <borntraeger@xxxxxxxxxx> writes: > Am 11.11.21 um 17:32 schrieb Paolo Bonzini: >> On 11/11/21 17:27, Vitaly Kuznetsov wrote: >>> This is a comtinuation of "KVM: x86: Drop arbitraty KVM_SOFT_MAX_VCPUS" >>> (https://lore.kernel.org/kvm/20211111134733.86601-1-vkuznets@xxxxxxxxxx/) >>> work. >>> >>> 1) Enforce KVM_CAP_NR_VCPUS <= KVM_CAP_MAX_VCPUS rule on all >>> architectures. [Sean Christopherson] >>> 2) Make KVM_CAP_NR_VCPUS return num_online_cpus() and not an arbitrary >>> value of '710' on x86. >>> >>> Everything but x86 was only 'eyeball tested', the change is trivial >>> but sorry in advance if I screwed up) >> >> Christian, can you look at this for s390? Returning a fixed value seems wrong for KVM_CAP_NR_VCPUS. > > If we talk about recommended number, then num_online_cpus() also seems to make sense on s390 so > if you change that for s390 as well I can ACK this. Thanks! For KVM_CAP_MAX_VCPUS s390 code returns one of the three things: KVM_S390_BSCA_CPU_SLOTS(64), KVM_MAX_VCPUS(255) or KVM_S390_ESCA_CPU_SLOTS(248). For KVM_CAP_NR_VCPUS, would it be better to return raw num_online_cpus(): diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 6a6dd5e1daf6..fcecbb762a1a 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -578,6 +578,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) r = MEM_OP_MAX_SIZE; break; case KVM_CAP_NR_VCPUS: + r = num_online_cpus(); + break; case KVM_CAP_MAX_VCPUS: case KVM_CAP_MAX_VCPU_ID: r = KVM_S390_BSCA_CPU_SLOTS; or cap KVM_CAP_MAX_VCPUS value with num_online_cpus(), e.g. diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 6a6dd5e1daf6..1cfe36f6432e 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -585,6 +585,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) r = KVM_MAX_VCPUS; else if (sclp.has_esca && sclp.has_64bscao) r = KVM_S390_ESCA_CPU_SLOTS; + if (ext == KVM_CAP_NR_VCPUS) + r = min_t(unsigned int, num_online_cpus(), r); break; case KVM_CAP_S390_COW: r = MACHINE_HAS_ESOP; For reference, see our ARM discussion: https://lore.kernel.org/kvm/20211111162746.100598-2-vkuznets@xxxxxxxxxx/ though 390's situation is different, the returned value for KVM_CAP_MAX_VCPUS is not VM-dependent. -- Vitaly
