powerpc/pseries: Receive payload with ibm,receive-hvpipe-msg RTAS

JIRA: https://issues.redhat.com/browse/RHEL-101849

Conflicts:
	- Use rtas_token() instead of rtas_function_token()
	- Use 0 for RTAS_SUCCESS (This definition needs upstream 9592aa5
	"powerpc/rtas: Add function return status constants")

commit cebdb52
Author: Haren Myneni <haren@linux.ibm.com>
Date:   Tue Sep 9 01:43:57 2025 -0700

    powerpc/pseries: Receive payload with ibm,receive-hvpipe-msg RTAS

    ibm,receive-hvpipe-msg RTAS call is used to receive data from the
    source (Ex: Hardware Management Console) over the hypervisor
    pipe. The hypervisor will signal the OS via a Hypervisor Pipe
    Event external interrupt when data is available to be received
    from the pipe and the event message has the source ID and the
    message type such as payload or closed pipe to the specific
    source. The hypervisor will not generate another interrupt for
    the next payload until the partition reads the previous payload.
    It means the hvpipe is blocked and will not deliver other events
    for any source. The maximum data length of 4048 bytes is
    supported with this RTAS call right now.

    The user space uses read() to receive data from HMC which issues
    ibm,receive-hvpipe-msg RTAS and the kernel returns the buffer
    length (including papr_hvpipe_hdr length) to the user space for
    success or RTAS failure error. If the message is regarding the
    pipe closed, kernel just returns the  papr_hvpipe_hdr with
    flags = HVPIPE_LOST_CONNECTION and expects the user space to
    close FD for the corresponding source.

    ibm,receive-hvpipe-msg RTAS call passes the buffer and returns
    the source ID from where this payload is received and the
    payload length.

    Signed-off-by: Haren Myneni <haren@linux.ibm.com>
    Tested-by: Shashank MS <shashank.gowda@in.ibm.com>
    Reviewed-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
    Reviewed-by: Tyrel Datwyler <tyreld@linux.ibm.com>
    Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
    Link: https://patch.msgid.link/20250909084402.1488456-6-haren@linux.ibm.com

Signed-off-by: Mamatha Inamdar <minamdar@redhat.com>

Author: Mamatha Inamdar

arch/powerpc/platforms/pseries/papr-hvpipe.c

@@ -60,6 +60,54 @@ static LIST_HEAD(hvpipe_src_list);
  *   return code for failure.
  */
 
+/*
+ * ibm,receive-hvpipe-msg RTAS call.
+ * @area: Caller-provided work area buffer for results.
+ * @srcID: Source ID returned by the RTAS call.
+ * @bytesw: Bytes written by RTAS call to @area.
+ */
+static int rtas_ibm_receive_hvpipe_msg(struct rtas_work_area *area,
+					u32 *srcID, u32 *bytesw)
+{
+	const s32 token = rtas_token("ibm,receive-hvpipe-msg");
+	u32 rets[2];
+	s32 fwrc;
+	int ret;
+
+	if (token == RTAS_UNKNOWN_SERVICE)
+		return -ENOENT;
+
+	do {
+		fwrc = rtas_call(token, 2, 3, rets,
+				rtas_work_area_phys(area),
+				rtas_work_area_size(area));
+
+	} while (rtas_busy_delay(fwrc));
+
+	switch (fwrc) {
+	case 0:		/* Success */
+		*srcID = rets[0];
+		*bytesw = rets[1];
+		ret = 0;
+		break;
+	case RTAS_HARDWARE_ERROR:
+		ret = -EIO;
+		break;
+	case RTAS_INVALID_PARAMETER:
+		ret = -EINVAL;
+		break;
+	case RTAS_FUNC_NOT_SUPPORTED:
+		ret = -EOPNOTSUPP;
+		break;
+	default:
+		ret = -EIO;
+		pr_err_ratelimited("unexpected ibm,receive-hvpipe-msg status %d\n", fwrc);
+		break;
+	}
+
+	return ret;
+}
+
 /*
  * ibm,send-hvpipe-msg RTAS call
  * @area: Caller-provided work area buffer to send.
@@ -116,9 +164,60 @@ static struct hvpipe_source_info *hvpipe_find_source(u32 srcID)
 	return NULL;
 }
 
+/*
+ * This work function collects receive buffer with recv HVPIPE
+ * RTAS call. Called from read()
+ * @buf: User specified buffer to copy the payload that returned
+ *       from recv HVPIPE RTAS.
+ * @size: Size of buffer user passed.
+ */
+static int hvpipe_rtas_recv_msg(char __user *buf, int size)
+{
+	struct rtas_work_area *work_area;
+	u32 srcID, bytes_written;
+	int ret;
+
+	work_area = rtas_work_area_alloc(SZ_4K);
+	if (!work_area) {
+		pr_err("Could not allocate RTAS buffer for recv pipe\n");
+		return -ENOMEM;
+	}
+
+	ret = rtas_ibm_receive_hvpipe_msg(work_area, &srcID,
+					&bytes_written);
+	if (!ret) {
+		/*
+		 * Recv HVPIPE RTAS is successful.
+		 * When releasing FD or no one is waiting on the
+		 * specific source, issue recv HVPIPE RTAS call
+		 * so that pipe is not blocked - this func is called
+		 * with NULL buf.
+		 */
+		if (buf) {
+			if (size < bytes_written) {
+				pr_err("Received the payload size = %d, but the buffer size = %d\n",
+					bytes_written, size);
+				bytes_written = size;
+			}
+			ret = copy_to_user(buf,
+					rtas_work_area_raw_buf(work_area),
+					bytes_written);
+			if (!ret)
+				ret = bytes_written;
+		}
+	} else {
+		pr_err("ibm,receive-hvpipe-msg failed with %d\n",
+				ret);
+	}
+
+	rtas_work_area_free(work_area);
+	return ret;
+}
+
 /*
  * papr_hvpipe_handle_write -  Issue send HVPIPE RTAS and return
- * the RTAS status to the user space
+ * the size (payload + HVPIPE_HDR_LEN) for RTAS success.
+ * Otherwise returns the status of RTAS to the user space
  */
 static ssize_t papr_hvpipe_handle_write(struct file *file,
 	const char __user *buf, size_t size, loff_t *off)
@@ -215,11 +314,72 @@ static ssize_t papr_hvpipe_handle_read(struct file *file,
 {
 
 	struct hvpipe_source_info *src_info = file->private_data;
+	struct papr_hvpipe_hdr hdr;
+	long ret;
 
 	if (!src_info)
 		return -EIO;
 
-	return 0;
+	/*
+	 * Max payload is 4048 (HVPIPE_MAX_WRITE_BUFFER_SIZE)
+	 */
+	if ((size > (HVPIPE_HDR_LEN + HVPIPE_MAX_WRITE_BUFFER_SIZE)) ||
+		(size < HVPIPE_HDR_LEN))
+		return -EINVAL;
+
+	/*
+	 * Payload is not available to receive or source pipe
+	 * is not closed.
+	 */
+	if (!src_info->hvpipe_status)
+		return 0;
+
+	hdr.version = 0;
+	hdr.flags = 0;
+
+	/*
+	 * In case if the hvpipe has payload and also the
+	 * hypervisor closed the pipe to the source, retrieve
+	 * the payload and return to the user space first and
+	 * then notify the userspace about the hvpipe close in
+	 * next read().
+	 */
+	if (src_info->hvpipe_status & HVPIPE_MSG_AVAILABLE)
+		hdr.flags = HVPIPE_MSG_AVAILABLE;
+	else if (src_info->hvpipe_status & HVPIPE_LOST_CONNECTION)
+		hdr.flags = HVPIPE_LOST_CONNECTION;
+	else
+		/*
+		 * Should not be here without one of the above
+		 * flags set
+		 */
+		return -EIO;
+
+	ret = copy_to_user(buf, &hdr, HVPIPE_HDR_LEN);
+	if (ret)
+		return ret;
+
+	/*
+	 * Message event has payload, so get the payload with
+	 * recv HVPIPE RTAS.
+	 */
+	if (hdr.flags & HVPIPE_MSG_AVAILABLE) {
+		ret = hvpipe_rtas_recv_msg(buf + HVPIPE_HDR_LEN,
+				size - HVPIPE_HDR_LEN);
+		if (ret > 0) {
+			src_info->hvpipe_status &= ~HVPIPE_MSG_AVAILABLE;
+			ret += HVPIPE_HDR_LEN;
+		}
+	} else if (hdr.flags & HVPIPE_LOST_CONNECTION) {
+		/*
+		 * Hypervisor is closing the pipe for the specific
+		 * source. So notify user space.
+		 */
+		src_info->hvpipe_status &= ~HVPIPE_LOST_CONNECTION;
+		ret = HVPIPE_HDR_LEN;
+	}
+
+	return ret;
 }
 
 /*

arch/powerpc/platforms/pseries/papr-hvpipe.h

@@ -14,6 +14,7 @@
 struct hvpipe_source_info {
 	struct list_head list;	/* list of sources */
 	u32 srcID;
+	u32 hvpipe_status;
 	wait_queue_head_t recv_wqh;	 /* wake up poll() waitq */
 	struct task_struct *tsk;
 };