On Mon, 21 Jan 2019 12:03:51 +0100
Cornelia Huck <cohuck@xxxxxxxxxx> wrote:
> Rework handling of multiple I/O requests to return -EAGAIN if
> we are already processing an I/O request. Introduce a mutex
> to disallow concurrent writes to the I/O region.
>
> The expectation is that userspace simply retries the operation
> if it gets -EAGAIN.
>
> We currently don't allow multiple ssch requests at the same
> time, as we don't have support for keeping channel programs
> around for more than one request.
>
> Signed-off-by: Cornelia Huck <cohuck@xxxxxxxxxx>
> ---
[..]
> static ssize_t vfio_ccw_mdev_write(struct mdev_device *mdev,
> @@ -188,25 +192,30 @@ 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 (private->state != VFIO_CCW_STATE_IDLE)
> + if (private->state == VFIO_CCW_STATE_NOT_OPER ||
> + private->state == VFIO_CCW_STATE_STANDBY)
> return -EACCES;
> + 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)) {
This might race with vfio_ccw_sch_io_todo() on
private->io_region->irb_area, or?
> + ret = -EFAULT;
> + goto out_unlock;
> + }
>
> vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_IO_REQ);
> - 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;
> }
>
[..]
