[qemu-s390x] [PATCH v4 3/6] vfio-ccw: protect the I/O region

[Cornelia Huck]

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.

Reviewed-by: Eric Farman <address@hidden>
Signed-off-by: Cornelia Huck <address@hidden>
---
 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;
-- 
2.17.2