diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0626e835e9eb..226c6cfe8062 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3939,7 +3939,9 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 			break;
 		fallthrough;
 	case KVM_CAP_DISABLE_QUIRKS:
+		mutex_lock(&kvm->lock);
 		kvm->arch.disabled_quirks |= cap->args[0] & kvm_caps.supported_quirks;
+		mutex_unlock(&kvm->lock);
 		r = 0;
 		break;
 	case KVM_CAP_SPLIT_IRQCHIP: {