powerpc/pseries: Wakeup hvpipe FD when the payload is pending

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

commit da24fb9
Author: Haren Myneni <haren@linux.ibm.com>
Date:   Tue Sep 9 01:43:58 2025 -0700

    powerpc/pseries: Wakeup hvpipe FD when the payload is pending

    The user space polls on the wait_queue for the payload from the
    specific source. The hypervisor interrupts the OS when the pipe
    status for the specific source is changed such as payload is
    available for the partition or pipe to the source is closed. The
    OS retrieves the HVPIPE event message with check-exception RTAS
    and event message contains the source ID and the pipe status.
    Then wakes up all FDs waiting on the wait_queue so that the user
    space can read the payload or close the FD if the pipe to source
    in the hypervisor is closed.

    The hypervisor assigns one pipe per partition for all sources.
    Hence issue  ibm,receive-hvpipe-msg() to read the pending
    payload during release() before closing FD so that pipe to the
    partition will not be blocked.

    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/20250909084402.1488456-7-haren@linux.ibm.com

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

Author: Mamatha Inamdar

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

@@ -396,6 +396,21 @@ static __poll_t papr_hvpipe_handle_poll(struct file *filp,
 	if (!src_info)
 		return POLLNVAL;
 
+	/*
+	 * If hvpipe already has pending payload, return so that
+	 * the user space can issue read().
+	 */
+	if (src_info->hvpipe_status)
+		return POLLIN | POLLRDNORM;
+
+	/*
+	 * Wait for the message event
+	 * hvpipe_event_interrupt() wakes up this wait_queue
+	 */
+	poll_wait(filp, &src_info->recv_wqh, wait);
+	if (src_info->hvpipe_status)
+		return POLLIN | POLLRDNORM;
+
 	return 0;
 }
 
@@ -413,7 +428,18 @@ static int papr_hvpipe_handle_release(struct inode *inode,
 	src_info = file->private_data;
 	list_del(&src_info->list);
 	file->private_data = NULL;
-	spin_unlock(&hvpipe_src_list_lock);
+	/*
+	 * If the pipe for this specific source has any pending
+	 * payload, issue recv HVPIPE RTAS so that pipe will not
+	 * be blocked.
+	 */
+	if (src_info->hvpipe_status & HVPIPE_MSG_AVAILABLE) {
+		src_info->hvpipe_status = 0;
+		spin_unlock(&hvpipe_src_list_lock);
+		hvpipe_rtas_recv_msg(NULL, 0);
+	} else
+		spin_unlock(&hvpipe_src_list_lock);
+
 	kfree(src_info);
 	return 0;
 }