diff options
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 21 | ||||
| -rw-r--r-- | arch/x86/include/asm/kvm_host.h | 6 | ||||
| -rw-r--r-- | arch/x86/kvm/x86.c | 20 |
3 files changed, 47 insertions, 0 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 94d73ec52aba..421479a67da5 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -7494,6 +7494,27 @@ The valid bits in cap.args[0] are: generate a #UD within the guest. =================================== ============================================ +7.32 KVM_CAP_MAX_VCPU_ID +------------------------ + +:Architectures: x86 +:Target: VM +:Parameters: args[0] - maximum APIC ID value set for current VM +:Returns: 0 on success, -EINVAL if args[0] is beyond KVM_MAX_VCPU_IDS + supported in KVM or if it has been set. + +This capability allows userspace to specify maximum possible APIC ID +assigned for current VM session prior to the creation of vCPUs, saving +memory for data structures indexed by the APIC ID. Userspace is able +to calculate the limit to APIC ID values from designated +CPU topology. + +The value can be changed only until KVM_ENABLE_CAP is set to a nonzero +value or until a vCPU is created. Upon creation of the first vCPU, +if the value was set to zero or KVM_ENABLE_CAP was not invoked, KVM +uses the return value of KVM_CHECK_EXTENSION(KVM_CAP_MAX_VCPU_ID) as +the maximum APIC ID. + 8. Other capabilities. ====================== diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 8109805b5429..9dc8d6d0a67d 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1243,6 +1243,12 @@ struct kvm_arch { hpa_t hv_root_tdp; spinlock_t hv_root_tdp_lock; #endif + /* + * VM-scope maximum vCPU ID. Used to determine the size of structures + * that increase along with the maximum vCPU ID, in which case, using + * the global KVM_MAX_VCPU_IDS may lead to significant memory waste. + */ + u32 max_vcpu_ids; }; struct kvm_vm_stat { diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 9c2e2b6d1767..25fbb90c7c93 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6087,6 +6087,20 @@ split_irqchip_unlock: } mutex_unlock(&kvm->lock); break; + case KVM_CAP_MAX_VCPU_ID: + r = -EINVAL; + if (cap->args[0] > KVM_MAX_VCPU_IDS) + break; + + mutex_lock(&kvm->lock); + if (kvm->arch.max_vcpu_ids == cap->args[0]) { + r = 0; + } else if (!kvm->arch.max_vcpu_ids) { + kvm->arch.max_vcpu_ids = cap->args[0]; + r = 0; + } + mutex_unlock(&kvm->lock); + break; default: r = -EINVAL; break; @@ -11246,6 +11260,12 @@ int kvm_arch_vcpu_precreate(struct kvm *kvm, unsigned int id) pr_warn_once("kvm: SMP vm created on host with unstable TSC; " "guest TSC will not be reliable\n"); + if (!kvm->arch.max_vcpu_ids) + kvm->arch.max_vcpu_ids = KVM_MAX_VCPU_IDS; + + if (id >= kvm->arch.max_vcpu_ids) + return -EINVAL; + return 0; } |