Re: [PATCH v3 3/6] vfio-ccw: protect the I/O region

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On 01/30/2019 08:22 AM, Cornelia Huck wrote:
Introduce a mutex to disallow concurrent reads or writes to the
I/O region. This makes sure that the data the kernel or user
space see is always consistent.

The same mutex will be used to protect the async region as well.

Signed-off-by: Cornelia Huck <cohuck@xxxxxxxxxx>

I keep wondering how the FSM could provide this, but I end up getting into chicken/egg rabbit holes. So, until my brain becomes wiser...

Reviewed-by: Eric Farman <farman@xxxxxxxxxxxxx>

---
  drivers/s390/cio/vfio_ccw_drv.c     |  3 +++
  drivers/s390/cio/vfio_ccw_ops.c     | 28 +++++++++++++++++++---------
  drivers/s390/cio/vfio_ccw_private.h |  2 ++
  3 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
index 0b3b9de45c60..5ea0da1dd954 100644
--- a/drivers/s390/cio/vfio_ccw_drv.c
+++ b/drivers/s390/cio/vfio_ccw_drv.c
@@ -84,7 +84,9 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work)
  		if (is_final)
  			cp_free(&private->cp);
  	}
+	mutex_lock(&private->io_mutex);
  	memcpy(private->io_region->irb_area, irb, sizeof(*irb));
+	mutex_unlock(&private->io_mutex);
if (private->io_trigger)
  		eventfd_signal(private->io_trigger, 1);
@@ -129,6 +131,7 @@ static int vfio_ccw_sch_probe(struct subchannel *sch)
private->sch = sch;
  	dev_set_drvdata(&sch->dev, private);
+	mutex_init(&private->io_mutex);
spin_lock_irq(sch->lock);
  	private->state = VFIO_CCW_STATE_NOT_OPER;
diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
index 3fdcc6dfe0bf..025c8a832bc8 100644
--- a/drivers/s390/cio/vfio_ccw_ops.c
+++ b/drivers/s390/cio/vfio_ccw_ops.c
@@ -169,16 +169,20 @@ static ssize_t vfio_ccw_mdev_read(struct mdev_device *mdev,
  {
  	struct vfio_ccw_private *private;
  	struct ccw_io_region *region;
+	int ret;
if (*ppos + count > sizeof(*region))
  		return -EINVAL;
private = dev_get_drvdata(mdev_parent_dev(mdev));
+	mutex_lock(&private->io_mutex);
  	region = private->io_region;
  	if (copy_to_user(buf, (void *)region + *ppos, count))
-		return -EFAULT;
-
-	return count;
+		ret = -EFAULT;
+	else
+		ret = count;
+	mutex_unlock(&private->io_mutex);
+	return ret;
  }
static ssize_t vfio_ccw_mdev_write(struct mdev_device *mdev,
@@ -188,23 +192,29 @@ static ssize_t vfio_ccw_mdev_write(struct mdev_device *mdev,
  {
  	struct vfio_ccw_private *private;
  	struct ccw_io_region *region;
+	int ret;
if (*ppos + count > sizeof(*region))
  		return -EINVAL;
private = dev_get_drvdata(mdev_parent_dev(mdev));
+	if (!mutex_trylock(&private->io_mutex))
+		return -EAGAIN;
region = private->io_region;
-	if (copy_from_user((void *)region + *ppos, buf, count))
-		return -EFAULT;
+	if (copy_from_user((void *)region + *ppos, buf, count)) {
+		ret = -EFAULT;
+		goto out_unlock;
+	}
vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_IO_REQ);
-	if (region->ret_code != 0) {
+	if (region->ret_code != 0)
  		private->state = VFIO_CCW_STATE_IDLE;
-		return region->ret_code;
-	}
+	ret = (region->ret_code != 0) ? region->ret_code : count;
- return count;
+out_unlock:
+	mutex_unlock(&private->io_mutex);
+	return ret;
  }
static int vfio_ccw_mdev_get_device_info(struct vfio_device_info *info)
diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h
index 50c52efb4fcb..32173cbd838d 100644
--- a/drivers/s390/cio/vfio_ccw_private.h
+++ b/drivers/s390/cio/vfio_ccw_private.h
@@ -28,6 +28,7 @@
   * @mdev: pointer to the mediated device
   * @nb: notifier for vfio events
   * @io_region: MMIO region to input/output I/O arguments/results
+ * @io_mutex: protect against concurrent update of I/O regions
   * @cp: channel program for the current I/O operation
   * @irb: irb info received from interrupt
   * @scsw: scsw info
@@ -42,6 +43,7 @@ struct vfio_ccw_private {
  	struct mdev_device	*mdev;
  	struct notifier_block	nb;
  	struct ccw_io_region	*io_region;
+	struct mutex		io_mutex;
struct channel_program cp;
  	struct irb		irb;





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