KVM: s390: pv: Add query interface

Some of the query information is already available via sysfs but
having a IOCTL makes the information easier to retrieve.
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Link: https://lore.kernel.org/r/20220517163629.3443-4-frankja@linux.ibm.com
Message-Id: <20220517163629.3443-4-frankja@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>

arch/s390/kvm/kvm-s390.c

@@ -2224,6 +2224,42 @@ static int kvm_s390_cpus_to_pv(struct kvm *kvm, u16 *rc, u16 *rrc)
 	return r;
 }
 
+/*
+ * Here we provide user space with a direct interface to query UV
+ * related data like UV maxima and available features as well as
+ * feature specific data.
+ *
+ * To facilitate future extension of the data structures we'll try to
+ * write data up to the maximum requested length.
+ */
+static ssize_t kvm_s390_handle_pv_info(struct kvm_s390_pv_info *info)
+{
+	ssize_t len_min;
+
+	switch (info->header.id) {
+	case KVM_PV_INFO_VM: {
+		len_min =  sizeof(info->header) + sizeof(info->vm);
+
+		if (info->header.len_max < len_min)
+			return -EINVAL;
+
+		memcpy(info->vm.inst_calls_list,
+		       uv_info.inst_calls_list,
+		       sizeof(uv_info.inst_calls_list));
+
+		/* It's max cpuid not max cpus, so it's off by one */
+		info->vm.max_cpus = uv_info.max_guest_cpu_id + 1;
+		info->vm.max_guests = uv_info.max_num_sec_conf;
+		info->vm.max_guest_addr = uv_info.max_sec_stor_addr;
+		info->vm.feature_indication = uv_info.uv_feature_indications;
+
+		return len_min;
+	}
+	default:
+		return -EINVAL;
+	}
+}
+
 static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
 {
 	int r = 0;
@@ -2360,6 +2396,46 @@ static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
 			     cmd->rc, cmd->rrc);
 		break;
 	}
+	case KVM_PV_INFO: {
+		struct kvm_s390_pv_info info = {};
+		ssize_t data_len;
+
+		/*
+		 * No need to check the VM protection here.
+		 *
+		 * Maybe user space wants to query some of the data
+		 * when the VM is still unprotected. If we see the
+		 * need to fence a new data command we can still
+		 * return an error in the info handler.
+		 */
+
+		r = -EFAULT;
+		if (copy_from_user(&info, argp, sizeof(info.header)))
+			break;
+
+		r = -EINVAL;
+		if (info.header.len_max < sizeof(info.header))
+			break;
+
+		data_len = kvm_s390_handle_pv_info(&info);
+		if (data_len < 0) {
+			r = data_len;
+			break;
+		}
+		/*
+		 * If a data command struct is extended (multiple
+		 * times) this can be used to determine how much of it
+		 * is valid.
+		 */
+		info.header.len_written = data_len;
+
+		r = -EFAULT;
+		if (copy_to_user(argp, &info, data_len))
+			break;
+
+		r = 0;
+		break;
+	}
 	default:
 		r = -ENOTTY;
 	}

include/uapi/linux/kvm.h

@@ -1660,6 +1660,30 @@ struct kvm_s390_pv_unp {
 	__u64 tweak;
 };
 
+enum pv_cmd_info_id {
+	KVM_PV_INFO_VM,
+};
+
+struct kvm_s390_pv_info_vm {
+	__u64 inst_calls_list[4];
+	__u64 max_cpus;
+	__u64 max_guests;
+	__u64 max_guest_addr;
+	__u64 feature_indication;
+};
+
+struct kvm_s390_pv_info_header {
+	__u32 id;
+	__u32 len_max;
+	__u32 len_written;
+	__u32 reserved;
+};
+
+struct kvm_s390_pv_info {
+	struct kvm_s390_pv_info_header header;
+	struct kvm_s390_pv_info_vm vm;
+};
+
 enum pv_cmd_id {
 	KVM_PV_ENABLE,
 	KVM_PV_DISABLE,
@@ -1668,6 +1692,7 @@ enum pv_cmd_id {
 	KVM_PV_VERIFY,
 	KVM_PV_PREP_RESET,
 	KVM_PV_UNSHARE_ALL,
+	KVM_PV_INFO,
 };
 
 struct kvm_pv_cmd {