[PATCH v8 07/15] s390/vfio-ap: File ops called to save the vfio device migration state

[Anthony Krowiak]

Implements the read callback function that was added to the
file_operations structure for the file created to save the state of the
vfio-ap device when the migration state transitioned from STOP to
to the STOP_COPY state.

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 state data will be transferred to the vfio_ap device driver on the
destination host when the state is transitioned to RESUMING.

Signed-off-by: Anthony Krowiak <akrowiak@xxxxxxxxxxxxx>
---
 drivers/s390/crypto/vfio_ap_migration.c | 284 +++++++++++++++++++++++-
 1 file changed, 274 insertions(+), 10 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_migration.c b/drivers/s390/crypto/vfio_ap_migration.c
index bbd007c06a77..0c43f25e2d9b 100644
--- a/drivers/s390/crypto/vfio_ap_migration.c
+++ b/drivers/s390/crypto/vfio_ap_migration.c
@@ -117,9 +117,10 @@ struct vfio_ap_config {
 static void
 vfio_ap_release_stop_copy_file(struct vfio_ap_migration_data *mig_data)
 {
-	/* Stub to be implemented when the mig_data->stop_copy_mig_file.ap_config
-	 * object is allocated.
-	 */
+	kvfree(mig_data->stop_copy_mig_file.ap_config);
+	mig_data->stop_copy_mig_file.ap_config = NULL;
+	mig_data->stop_copy_mig_file.config_sz = 0;
+	mig_data->stop_copy_mig_file.filp = NULL;
 }
 
 static void vfio_ap_release_resuming_file(struct vfio_ap_migration_data *mig_data)
@@ -129,13 +130,6 @@ static void vfio_ap_release_resuming_file(struct vfio_ap_migration_data *mig_dat
 	 */
 }
 
-static ssize_t
-vfio_ap_stop_copy_read(struct file *, char __user *, size_t, loff_t *)
-{
-	/* TODO */
-	return -EOPNOTSUPP;
-}
-
 static int vfio_ap_release_mig_file(struct inode *file_inode, struct file *filp)
 {
 	struct ap_matrix_mdev *matrix_mdev = filp->private_data;
@@ -150,6 +144,276 @@ static int vfio_ap_release_mig_file(struct inode *file_inode, struct file *filp)
 	return 0;
 }
 
+/**
+ * validate_stop_copy_read_parms: Validate the input parameters to the
+ *                                vfio_ap_stop_copy_read function
+ *
+ * @filp: Pointer to the file stream used to read the vfio-ap device state
+ * @len:  The length of the data to be read
+ *
+ * Verify the following:
+ * - @filp private data is an ap_matrix_mdev instance
+ * - @filp is the instance opened when state transitioned from STOP to STOP_COPY
+ * - @filp->f_pos + @len does not cause integer overflow
+ *
+ * Returns: 0 if the parameters pass validation; otherwise returns an error
+ */
+static int validate_stop_copy_read_parms(struct file *filp, size_t len)
+{
+	struct vfio_ap_migration_data *mig_data;
+	struct ap_matrix_mdev *matrix_mdev;
+	loff_t total_len;
+
+	lockdep_assert_held(&matrix_dev->mdevs_lock);
+
+	if (check_add_overflow((loff_t)len, filp->f_pos, &total_len))
+		return -EIO;
+
+	/*
+	 * matrix_mdev is guaranteed live here: vfio_ap_open_file_stream() took
+	 * a vfio_device registration reference that is held until
+	 * vfio_ap_release_mig_file() runs, so the embedding matrix_mdev cannot
+	 * be freed while this file descriptor is open.
+	 */
+	matrix_mdev = filp->private_data;
+
+	if (!matrix_mdev->mig_data)
+		return -ENODEV;
+
+	mig_data = matrix_mdev->mig_data;
+
+	if (mig_data->stop_copy_mig_file.filp != filp)
+		return -EINVAL;
+
+	return 0;
+}
+
+static size_t vfio_ap_config_size(struct ap_matrix_mdev *matrix_mdev,
+				  int *num_queues)
+{
+	size_t qinfo_size;
+
+	lockdep_assert_held(&matrix_dev->mdevs_lock);
+
+	*num_queues = vfio_ap_mdev_get_num_queues(&matrix_mdev->shadow_apcb);
+	qinfo_size = *num_queues * sizeof(struct vfio_ap_queue_info);
+
+	return qinfo_size + sizeof(struct vfio_ap_config);
+}
+
+static int get_hardware_info_for_queue(const char *mdev_name,
+				       struct ap_tapq_hwinfo *hwinfo,
+				       unsigned long apqn)
+{
+	struct ap_queue_status status;
+
+	status = ap_tapq(apqn, hwinfo);
+
+	switch (status.response_code) {
+	case AP_RESPONSE_NORMAL:
+	case AP_RESPONSE_RESET_IN_PROGRESS:
+	case AP_RESPONSE_DECONFIGURED:
+	case AP_RESPONSE_CHECKSTOPPED:
+	case AP_RESPONSE_BUSY:
+		/* For all these RCs the tapq info should be available */
+		return 0;
+	case AP_RESPONSE_Q_NOT_AVAIL:
+		pr_err_ratelimited("vfio_ap_mdev %s: Failed to get hwinfo for queue %02lx.%04lx: TAPQ rc=%d",
+				   mdev_name, AP_QID_CARD(apqn), AP_QID_QUEUE(apqn),
+				   status.response_code);
+		return -ENODEV;
+	default:
+		/*
+		 * Without a pending async error, the tapq info should be
+		 * available
+		 */
+		if (status.async)
+			return 0;
+
+		pr_err_ratelimited("vfio_ap_mdev %s:Failed to get hwinfo for queue %02lx.%04lx: TAPQ rc=%d",
+				   mdev_name, AP_QID_CARD(apqn), AP_QID_QUEUE(apqn),
+				   status.response_code);
+		return -EIO;
+	}
+}
+
+/**
+ * vfio_ap_store_queue_info:
+ *
+ * Stores the hardware information returned from the PQAP(TAPQ) command for each
+ * queue device identified in the 'qinfo' field of the a vfio_ap_config
+ * object. The APQNs in the 'qinfo' field must already have been snapshotted
+ * prior to calling this function.
+ *
+ * @mdev_name:	The name (UUID) of the mediated device to use in log messages
+ * @ap_config:	A reference to the vfio_ap_config instance in which to store
+ *		the queue information. It is expected that each APQN identifying
+ *		a queue device for which hardware information is to be retrieved
+ *		shall be snapshotted prior to calling this function.
+ *
+ * Returns:	Zero (0) if the hardware information is retrieved for each queue
+ *		device in the AP configuration; otherwise, returns an error.
+ */
+static int vfio_ap_store_queue_info(const char *mdev_name,
+				    struct vfio_ap_config *ap_config)
+{
+	struct ap_tapq_hwinfo source_hwinfo;
+	unsigned long num_queues;
+	int ret;
+
+	for (num_queues = 0; num_queues < ap_config->num_queues; num_queues++) {
+		ret = get_hardware_info_for_queue(mdev_name, &source_hwinfo,
+						  ap_config->qinfo[num_queues].apqn);
+		if (ret)
+			return ret;
+
+		ap_config->qinfo[num_queues].data = source_hwinfo.value;
+	}
+
+	return 0;
+}
+
+static int vfio_ap_get_config(struct ap_matrix_mdev *matrix_mdev)
+{
+	struct vfio_ap_config *ap_configuration;
+	unsigned long *apm, *aqm, apid, apqi;
+	unsigned int num_queues;
+	const char *mdev_name;
+	size_t ap_config_size;
+	int ret, qindex;
+
+	lockdep_assert_held(&matrix_dev->mdevs_lock);
+
+	ap_config_size = vfio_ap_config_size(matrix_mdev, (int *)&num_queues);
+
+	ap_configuration = kvzalloc(ap_config_size, GFP_KERNEL_ACCOUNT);
+	if (!ap_configuration)
+		return -ENOMEM;
+
+	ap_configuration->magic   = VFIO_AP_MIG_MAGIC;
+	ap_configuration->version = VFIO_AP_MIG_VERSION;
+
+	/*
+	 * num_queues must be set before writing qinfo[] elements; the
+	 * __counted_by(num_queues) annotation on qinfo[] causes the compiler to
+	 * insert bounds checks that evaluate against ap_configuration->num_queues.
+	 * Writing through qinfo[i] with num_queues still 0 would trap.
+	 */
+	ap_configuration->num_queues = num_queues;
+
+	apm = matrix_mdev->shadow_apcb.apm;
+	aqm = matrix_mdev->shadow_apcb.aqm;
+	qindex = 0;
+	for_each_set_bit_inv(apid, apm, AP_DEVICES) {
+		for_each_set_bit_inv(apqi, aqm, AP_DOMAINS) {
+			ap_configuration->qinfo[qindex].apqn =
+				AP_MKQID(apid, apqi);
+			qindex += 1;
+		}
+	}
+	memcpy(ap_configuration->adm, matrix_mdev->shadow_apcb.adm,
+	       sizeof(ap_configuration->adm));
+	mdev_name = dev_name(matrix_mdev->vdev.dev);
+
+	ret = vfio_ap_store_queue_info(mdev_name, ap_configuration);
+	if (ret) {
+		kvfree(ap_configuration);
+		return ret;
+	}
+
+	matrix_mdev->mig_data->stop_copy_mig_file.ap_config = ap_configuration;
+	matrix_mdev->mig_data->stop_copy_mig_file.config_sz = ap_config_size;
+
+	return 0;
+}
+
+static ssize_t vfio_ap_stop_copy_read(struct file *filp, char __user *buf,
+				      size_t len, loff_t *pos)
+{
+	struct vfio_ap_migration_file *mig_file;
+	struct ap_matrix_mdev *matrix_mdev;
+	loff_t read_pos;
+	ssize_t ret;
+
+	/*
+	 * This file was opened with stream_open(), so pos should be NULL for
+	 * sequential read() calls; a non-NULL pointer will be passed only
+	 * for positional pread() calls in which case we return an error
+	 * indicating broken pipe/illegal seek on a non-seekable file
+	 */
+	if (pos)
+		return -ESPIPE;
+
+	mutex_lock(&matrix_dev->mdevs_lock);
+
+	pos = &filp->f_pos;
+
+	ret = validate_stop_copy_read_parms(filp, len);
+	if (ret) {
+		mutex_unlock(&matrix_dev->mdevs_lock);
+		return ret;
+	}
+
+	matrix_mdev = filp->private_data;
+	mig_file = &matrix_mdev->mig_data->stop_copy_mig_file;
+
+	/*
+	 * Lazy initialization: the migration config is generated on the first
+	 * read() call. vfio_ap_open_file_stream() initializes ap_config to NULL
+	 * and config_sz to 0. On first read, we generate the config by
+	 * snapshotting the guest's APQNs from shadow_apcb and retrieving hardware
+	 * info via TAPQ for each queue. The result is cached in mig_file->ap_config
+	 * for subsequent read() calls. The config is freed when the migration FD
+	 * is released (vfio_ap_release_mig_file -> vfio_ap_release_stop_copy_file).
+	 */
+	if (!mig_file->ap_config) {
+		ret = vfio_ap_get_config(matrix_mdev);
+		if (ret) {
+			mutex_unlock(&matrix_dev->mdevs_lock);
+			return ret;
+		}
+	}
+
+	/*
+	 * Compute the offset and clamped length fully under the lock so that
+	 * concurrent read()s on this stream file each see a consistent view of
+	 * the current position.  *pos is advanced here while we still hold the
+	 * lock; copy_to_user() then uses the snapshot read_pos.  This prevents
+	 * two threads from calculating the same offset and both copying the
+	 * same region (or one reading past the end of the buffer).
+	 */
+	if (*pos >= mig_file->config_sz) {
+		mutex_unlock(&matrix_dev->mdevs_lock);
+		return 0;
+	}
+
+	len = min_t(size_t, mig_file->config_sz - *pos, len);
+	if (len == 0) {
+		mutex_unlock(&matrix_dev->mdevs_lock);
+		return 0;
+	}
+
+	read_pos = *pos;
+	*pos += len;
+
+	/*
+	 * Keep mdevs_lock held across copy_to_user() to prevent a concurrent
+	 * vfio_ap_reset_migration_state() from freeing ap_config while we are
+	 * reading it.  copy_to_user() may fault on a non-resident user page,
+	 * but that is legal for a sleeping mutex.  The data transferred is at
+	 * most a few KB for any realistic AP configuration, so holding the lock
+	 * here is acceptable.
+	 */
+	if (copy_to_user(buf, (char *)mig_file->ap_config + read_pos, len)) {
+		mutex_unlock(&matrix_dev->mdevs_lock);
+		return -EFAULT;
+	}
+
+	mutex_unlock(&matrix_dev->mdevs_lock);
+
+	return len;
+}
+
 static const struct file_operations vfio_ap_stop_copy_fops = {
 	.owner = THIS_MODULE,
 	.read = vfio_ap_stop_copy_read,
-- 
2.53.0