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

Eric Farman
2019-02-08T21:26:06Z

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@redhat.com>

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@linux.ibm.com>

> ---
> 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;
>