vfio: ccw: introduce ccw_io_region

To provide user-space a set of interfaces to:
1. pass in a ccw program to perform an I/O operation.
2. read back I/O results of the completed I/O operations.
We introduce an MMIO region for the vfio-ccw device here.

This region is defined to content:
1. areas to store arguments that an ssch required.
2. areas to store the I/O results.

Using pwrite/pread to the device on this region, a user-space program
could write/read data to/from the vfio-ccw device.

Reviewed-by: Pierre Morel <[e-mail]>
Signed-off-by: Dong Jia Shi <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Cornelia Huck <[e-mail]>

drivers/s390/cio/vfio_ccw_ops.c

···
 				 &private->nb);
 }
 
+static ssize_t vfio_ccw_mdev_read(struct mdev_device *mdev,
+				  char __user *buf,
+				  size_t count,
+				  loff_t *ppos)
+{
+	struct vfio_ccw_private *private;
+	struct ccw_io_region *region;
+
+	if (*ppos + count > sizeof(*region))
+		return -EINVAL;
+
+	private = dev_get_drvdata(mdev_parent_dev(mdev));
+	if (!private)
+		return -ENODEV;
+
+	region = &private->io_region;
+	if (copy_to_user(buf, (void *)region + *ppos, count))
+		return -EFAULT;
+
+	return count;
+}
+
+static ssize_t vfio_ccw_mdev_write(struct mdev_device *mdev,
+				   const char __user *buf,
+				   size_t count,
+				   loff_t *ppos)
+{
+	struct vfio_ccw_private *private;
+	struct ccw_io_region *region;
+
+	if (*ppos + count > sizeof(*region))
+		return -EINVAL;
+
+	private = dev_get_drvdata(mdev_parent_dev(mdev));
+	if (!private)
+		return -ENODEV;
+
+	region = &private->io_region;
+	if (copy_from_user((void *)region + *ppos, buf, count))
+		return -EFAULT;
+	region->ret_code = 0;
+
+	return count;
+}
+
 static const struct mdev_parent_ops vfio_ccw_mdev_ops = {
 	.owner			= THIS_MODULE,
 	.supported_type_groups  = mdev_type_groups,
···
 	.remove			= vfio_ccw_mdev_remove,
 	.open			= vfio_ccw_mdev_open,
 	.release		= vfio_ccw_mdev_release,
+	.read			= vfio_ccw_mdev_read,
+	.write			= vfio_ccw_mdev_write,
 };
 
 int vfio_ccw_mdev_reg(struct subchannel *sch)

drivers/s390/cio/vfio_ccw_private.h

···
 #ifndef _VFIO_CCW_PRIVATE_H_
 #define _VFIO_CCW_PRIVATE_H_
 
+#include <linux/vfio_ccw.h>
+
 #include "css.h"
 
 /**
···
  * @avail: available for creating a mediated device
  * @mdev: pointer to the mediated device
  * @nb: notifier for vfio events
+ * @io_region: MMIO region to input/output I/O arguments/results
  */
 struct vfio_ccw_private {
 	struct subchannel	*sch;
···
 	atomic_t		avail;
 	struct mdev_device	*mdev;
 	struct notifier_block	nb;
+	struct ccw_io_region	io_region;
 } __aligned(8);
 
 extern int vfio_ccw_mdev_reg(struct subchannel *sch);

include/uapi/linux/vfio_ccw.h

···
+/*
+ * Interfaces for vfio-ccw
+ *
+ * Copyright IBM Corp. 2017
+ *
+ * Author(s): Dong Jia Shi <[e-mail]>
+ */
+
+#ifndef _VFIO_CCW_H_
+#define _VFIO_CCW_H_
+
+#include <linux/types.h>
+
+struct ccw_io_region {
+#define ORB_AREA_SIZE 12
+	__u8	orb_area[ORB_AREA_SIZE];
+#define SCSW_AREA_SIZE 12
+	__u8	scsw_area[SCSW_AREA_SIZE];
+#define IRB_AREA_SIZE 96
+	__u8	irb_area[IRB_AREA_SIZE];
+	__u32	ret_code;
+} __packed;
+
+#endif