KVM: x86: Allow userspace to set maximum VCPU id for VM
Introduce new max_vcpu_ids in KVM for x86 architecture. Userspace
can assign maximum possible vcpu id for current VM session using
KVM_CAP_MAX_VCPU_ID of KVM_ENABLE_CAP ioctl().
This is done for x86 only because the sole use case is to guide
memory allocation for PID-pointer table, a structure needed to
enable VMX IPI.
By default, max_vcpu_ids set as KVM_MAX_VCPU_IDS.
Suggested-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Zeng Guang <guang.zeng@intel.com>
Message-Id: <20220419154444.11888-1-guang.zeng@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9c2e2b6..25fbb90 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6087,6 +6087,20 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
}
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;
}
