Implements two callback functions that were added to the 'file_operations'
structure for the file created to save the state of the vfio device
when the migration state transitioned from VFIO_DEVICE_STATE_STOP to
VFIO_DEVICE_STATE_STOP_COPY:

* Read callback

  This function copies the guest's AP configuration information to
  userspace. The information copied is comprised of the APQN of each queue
  device passed through to the guest along with its hardware information.
  This data will be used to verify the source and target guests have
  compatible AP configurations.

* Release callback

  This function deallocates the object used to save the state of the
  vfio device.

Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_migration.c | 78 +++++++++++++++++++++++--
 1 file changed, 72 insertions(+), 6 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_migration.c b/drivers/s390/crypto/vfio_ap_migration.c
index 21734d3ed7b7..aadc362edf78 100644
--- a/drivers/s390/crypto/vfio_ap_migration.c
+++ b/drivers/s390/crypto/vfio_ap_migration.c
@@ -98,16 +98,82 @@ static void vfio_ap_release_mig_files(struct ap_matrix_mdev *matrix_mdev)
 	}
 }
 
-static ssize_t vfio_ap_save_read(struct file *, char __user *, size_t, loff_t *)
+static ssize_t validate_save_read_parms(struct vfio_ap_migration_file *migf,
+					loff_t *pos, size_t len)
 {
-	/* TODO */
-	return -EOPNOTSUPP;
+	lockdep_assert_held(&matrix_dev->mdevs_lock);
+
+	if (migf->disabled) {
+		dev_err(migf->matrix_mdev->vdev.dev,
+			"%s (%d): migration file is disabled\n",
+			__func__, __LINE__);
+		return -ENODEV;
+	}
+
+	if (*pos > migf->config_sz) {
+		dev_err(migf->matrix_mdev->vdev.dev,
+			"%s (%d): file pos (%llu) exceeds migf->config size (%zu)\n",
+			__func__, __LINE__, *pos, migf->config_sz);
+		return -EINVAL;
+	}
+
+	return 0;
 }
 
-static int vfio_ap_release_migf(struct inode *, struct file *)
+static ssize_t vfio_ap_save_read(struct file *filp, char __user *buf,
+				 size_t len, loff_t *pos)
 {
-	/* TODO */
-	return -EOPNOTSUPP;
+	struct vfio_ap_migration_file *migf;
+	ssize_t ret = 0;
+
+	if (pos)
+		return -ESPIPE;
+
+	mutex_lock(&matrix_dev->mdevs_lock);
+
+	pos = &filp->f_pos;
+	migf = filp->private_data;
+
+	ret = validate_save_read_parms(migf, pos, len);
+	if (ret)
+		goto out_unlock;
+
+	len = min_t(size_t, migf->config_sz - *pos, len);
+	if (len) {
+		if (copy_to_user(buf, (void *)migf->ap_config + *pos, len)) {
+			ret = -EFAULT;
+			dev_err(migf->matrix_mdev->vdev.dev,
+				"%s (%d): failed to copy config data to user\n",
+				__func__, __LINE__);
+			goto out_unlock;
+		}
+
+		*pos += len;
+		ret = len;
+	}
+
+	dev_dbg(migf->matrix_mdev->vdev.dev,
+		"%s (%d): copied %zu bytes of AP config data to user\n",
+		__func__, __LINE__, len);
+
+out_unlock:
+	mutex_unlock(&matrix_dev->mdevs_lock);
+
+	return ret;
+}
+
+static void vfio_ap_deallocate_migf(struct vfio_ap_migration_file *migf);
+
+static int vfio_ap_release_migf(struct inode *inode, struct file *filp)
+{
+	struct vfio_ap_migration_file *migf;
+
+	mutex_lock(&matrix_dev->mdevs_lock);
+	migf = filp->private_data;
+	vfio_ap_deallocate_migf(migf);
+	mutex_unlock(&matrix_dev->mdevs_lock);
+
+	return 0;
 }
 
 static const struct file_operations vfio_ap_save_fops = {
-- 
2.52.0