Merge tag 'vfio-ccw-20210520' of https://git.kernel.org/pub/scm/linux/kernel/git/kvms390/vfio-ccw into fixes

Avoid some races in vfio-ccw request handling.

* tag 'vfio-ccw-20210520' of https://git.kernel.org/pub/scm/linux/kernel/git/kvms390/vfio-ccw:
  vfio-ccw: Serialize FSM IDLE state with I/O completion
  vfio-ccw: Reset FSM state to IDLE inside FSM
  vfio-ccw: Check initialized flag in cp_init()

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

Author: Vasily Gorbik

drivers/s390/cio/vfio_ccw_cp.c

@@ -638,6 +638,10 @@ int cp_init(struct channel_program *cp, struct device *mdev, union orb *orb)
 	static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 1);
 	int ret;
 
+	/* this is an error in the caller */
+	if (cp->initialized)
+		return -EBUSY;
+
 	/*
 	 * We only support prefetching the channel program. We assume all channel
 	 * programs executed by supported guests likewise support prefetching.

drivers/s390/cio/vfio_ccw_drv.c

@@ -86,6 +86,7 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work)
 	struct vfio_ccw_private *private;
 	struct irb *irb;
 	bool is_final;
+	bool cp_is_finished = false;
 
 	private = container_of(work, struct vfio_ccw_private, io_work);
 	irb = &private->irb;
@@ -94,14 +95,21 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work)
 		     (SCSW_ACTL_DEVACT | SCSW_ACTL_SCHACT));
 	if (scsw_is_solicited(&irb->scsw)) {
 		cp_update_scsw(&private->cp, &irb->scsw);
-		if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING)
+		if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING) {
 			cp_free(&private->cp);
+			cp_is_finished = true;
+		}
 	}
 	mutex_lock(&private->io_mutex);
 	memcpy(private->io_region->irb_area, irb, sizeof(*irb));
 	mutex_unlock(&private->io_mutex);
 
-	if (private->mdev && is_final)
+	/*
+	 * Reset to IDLE only if processing of a channel program
+	 * has finished. Do not overwrite a possible processing
+	 * state if the final interrupt was for HSCH or CSCH.
+	 */
+	if (private->mdev && cp_is_finished)
 		private->state = VFIO_CCW_STATE_IDLE;
 
 	if (private->io_trigger)

drivers/s390/cio/vfio_ccw_fsm.c

@@ -318,6 +318,7 @@ static void fsm_io_request(struct vfio_ccw_private *private,
 	}
 
 err_out:
+	private->state = VFIO_CCW_STATE_IDLE;
 	trace_vfio_ccw_fsm_io_request(scsw->cmd.fctl, schid,
 				      io_region->ret_code, errstr);
 }

drivers/s390/cio/vfio_ccw_ops.c

@@ -279,8 +279,6 @@ static ssize_t vfio_ccw_mdev_write_io_region(struct vfio_ccw_private *private,
 	}
 
 	vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_IO_REQ);
-	if (region->ret_code != 0)
-		private->state = VFIO_CCW_STATE_IDLE;
 	ret = (region->ret_code != 0) ? region->ret_code : count;
 
 out_unlock: