[PATCH v2 7/7] s390/vfio_ccw: implement a crw lock

[Eric Farman]

Unlike the channel_program struct, which covers synchronous I/O
submissions and asynchronous interrupts, the CRW region relies
exclusively on asynchronous events coming from hardware.

Implement a lock to manage the list of those payloads, to ensure
they are read cohesively.

Signed-off-by: Eric Farman <farman@xxxxxxxxxxxxx>
---
 drivers/s390/cio/vfio_ccw_chp.c     | 15 ++++++++++-----
 drivers/s390/cio/vfio_ccw_drv.c     |  4 ++++
 drivers/s390/cio/vfio_ccw_ops.c     |  3 +++
 drivers/s390/cio/vfio_ccw_private.h |  2 ++
 4 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/s390/cio/vfio_ccw_chp.c b/drivers/s390/cio/vfio_ccw_chp.c
index 38c176cf6295..bbc445efd67f 100644
--- a/drivers/s390/cio/vfio_ccw_chp.c
+++ b/drivers/s390/cio/vfio_ccw_chp.c
@@ -90,14 +90,18 @@ static ssize_t vfio_ccw_crw_region_read(struct vfio_ccw_private *private,
 	if (pos + count > sizeof(*region))
 		return -EINVAL;
 
+	mutex_lock(&private->io_mutex);
+	region = private->region[i].data;
+
+	spin_lock(&private->crw_lock);
 	crw = list_first_entry_or_null(&private->crw,
 				       struct vfio_ccw_crw, next);
 
 	if (crw)
 		list_del(&crw->next);
 
-	mutex_lock(&private->io_mutex);
-	region = private->region[i].data;
+	/* Drop CRW lock while copying to userspace */
+	spin_unlock(&private->crw_lock);
 
 	if (crw)
 		memcpy(&region->crw, &crw->crw, sizeof(region->crw));
@@ -108,14 +112,15 @@ static ssize_t vfio_ccw_crw_region_read(struct vfio_ccw_private *private,
 		ret = count;
 
 	region->crw = 0;
-
-	mutex_unlock(&private->io_mutex);
-
 	kfree(crw);
 
 	/* Notify the guest if more CRWs are on our queue */
+	spin_lock(&private->crw_lock);
 	if (!list_empty(&private->crw) && private->crw_trigger)
 		eventfd_signal(private->crw_trigger);
+	spin_unlock(&private->crw_lock);
+
+	mutex_unlock(&private->io_mutex);
 
 	return ret;
 }
diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
index bfb68de6e52c..12edccb62cbf 100644
--- a/drivers/s390/cio/vfio_ccw_drv.c
+++ b/drivers/s390/cio/vfio_ccw_drv.c
@@ -125,8 +125,10 @@ void vfio_ccw_crw_todo(struct work_struct *work)
 
 	private = container_of(work, struct vfio_ccw_private, crw_work);
 
+	spin_lock(&private->crw_lock);
 	if (!list_empty(&private->crw) && private->crw_trigger)
 		eventfd_signal(private->crw_trigger);
+	spin_unlock(&private->crw_lock);
 }
 
 /*
@@ -296,7 +298,9 @@ static void vfio_ccw_queue_crw(struct vfio_ccw_private *private,
 	crw->crw.erc = erc;
 	crw->crw.rsid = rsid;
 
+	spin_lock(&private->crw_lock);
 	list_add_tail(&crw->next, &private->crw);
+	spin_unlock(&private->crw_lock);
 	queue_work(vfio_ccw_work_q, &private->crw_work);
 }
 
diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
index d2475b3158cf..b3699ffd2f1d 100644
--- a/drivers/s390/cio/vfio_ccw_ops.c
+++ b/drivers/s390/cio/vfio_ccw_ops.c
@@ -60,6 +60,7 @@ static int vfio_ccw_mdev_init_dev(struct vfio_device *vdev)
 	INIT_WORK(&private->io_work, vfio_ccw_sch_io_todo);
 	INIT_WORK(&private->crw_work, vfio_ccw_crw_todo);
 	spin_lock_init(&private->cp_lock);
+	spin_lock_init(&private->crw_lock);
 
 	private->cp.guest_cp = kzalloc_objs(struct ccw1, CCWCHAIN_LEN_MAX);
 	if (!private->cp.guest_cp)
@@ -137,10 +138,12 @@ static void vfio_ccw_mdev_release_dev(struct vfio_device *vdev)
 		container_of(vdev, struct vfio_ccw_private, vdev);
 	struct vfio_ccw_crw *crw, *temp;
 
+	spin_lock(&private->crw_lock);
 	list_for_each_entry_safe(crw, temp, &private->crw, next) {
 		list_del(&crw->next);
 		kfree(crw);
 	}
+	spin_unlock(&private->crw_lock);
 
 	kmem_cache_free(vfio_ccw_crw_region, private->crw_region);
 	kmem_cache_free(vfio_ccw_schib_region, private->schib_region);
diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h
index 061b594fde36..4a43609d6422 100644
--- a/drivers/s390/cio/vfio_ccw_private.h
+++ b/drivers/s390/cio/vfio_ccw_private.h
@@ -120,6 +120,8 @@ struct vfio_ccw_private {
 
 	struct irb		irb;
 	union scsw		scsw;
+
+	spinlock_t		crw_lock;
 	struct list_head	crw;
 
 	struct eventfd_ctx	*io_trigger;
-- 
2.53.0